This document describes the stabs debugging symbol tables.
Copyright 1992, 1993 Free Software Foundation, Inc.
-Contributed by Cygnus Support. Written by Julia Menapace.
+Contributed by Cygnus Support. Written by Julia Menapace, Jim Kingdon,
+and David MacKenzie.
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
@menu
* Overview:: Overview of stabs
-* Program structure:: Encoding of the structure of the program
+* Program Structure:: Encoding of the structure of the program
* Constants:: Constants
* Variables::
* Types:: Type definitions
-* Symbol tables:: Symbol information in symbol tables
+* Symbol Tables:: Symbol information in symbol tables
* Cplusplus:: Appendixes:
-* Stab types:: Symbol types in a.out files
-* Symbol descriptors:: Table of Symbol descriptors
-* Type descriptors:: Table of Symbol descriptors
-* Expanded reference:: Reference information by stab type
+* Stab Types:: Symbol types in a.out files
+* Symbol Descriptors:: Table of symbol descriptors
+* Type Descriptors:: Table of type descriptors
+* Expanded Reference:: Reference information by stab type
* Questions:: Questions and anomolies
-* XCOFF differences:: Differences between GNU stabs in a.out
+* XCOFF Differences:: Differences between GNU stabs in a.out
and GNU stabs in XCOFF
-* Sun differences:: Differences between GNU stabs and Sun
+* Sun Differences:: Differences between GNU stabs and Sun
native stabs
-* Stabs in ELF:: Stabs in an ELF file.
-* Symbol Types Index:: Index of symbolic stab symbol type names.
+* Stabs In ELF:: Stabs in an ELF file.
+* Symbol Types Index:: Index of symbolic stab symbol type names.
@end menu
@end ifinfo
@node Overview
-@chapter Overview of stabs
+@chapter Overview of Stabs
@dfn{Stabs} refers to a format for information that describes a program
to a debugger. This format was apparently invented by
This document is one of the few published sources of documentation on
stabs. It is believed to be comprehensive for stabs used by C. The
-lists of symbol descriptors (@pxref{Symbol descriptors}) and type
-descriptors (@pxref{Type descriptors}) are believed to be completely
+lists of symbol descriptors (@pxref{Symbol Descriptors}) and type
+descriptors (@pxref{Type Descriptors}) are believed to be completely
comprehensive. Stabs for COBOL-specific features and for variant
records (used by Pascal and Modula-2) are poorly documented here.
@menu
* Flow:: Overview of debugging information flow
-* Stabs format:: Overview of stab format
-* String field:: The @code{.stabs} @var{string} field
-* C example:: A simple example in C source
-* Assembly code:: The simple example at the assembly level
+* Stabs Format:: Overview of stab format
+* String Field:: The string field
+* C Example:: A simple example in C source
+* Assembly Code:: The simple example at the assembly level
@end menu
@node Flow
-@section Overview of debugging information flow
+@section Overview of Debugging Information Flow
The GNU C compiler compiles C source in a @file{.c} file into assembly
language in a @file{.s} file, which the assembler translates into
table. Debuggers use the symbol and string tables in the executable as
a source of debugging information about the program.
-@node Stabs format
-@section Overview of stab format
+@node Stabs Format
+@section Overview of Stab Format
There are three overall formats for stab assembler directives,
differentiated by the first word of the stab. The name of the directive
The overall format of each class of stab is:
@example
-.stabs "@var{string}",@var{type},0,@var{desc},@var{value}
-.stabn @var{type},0,@var{desc},@var{value}
-.stabd @var{type},0,@var{desc}
+.stabs "@var{string}",@var{type},@var{other},@var{desc},@var{value}
+.stabn @var{type},@var{other},@var{desc},@var{value}
+.stabd @var{type},@var{other},@var{desc}
.stabx "@var{string}",@var{value},@var{type},@var{sdb-type}
@end example
@c what is the correct term for "current file location"? My AIX
@c assembler manual calls it "the value of the current location counter".
For @code{.stabn} and @code{.stabd}, there is no @var{string} (the
-@code{n_strx} field is zero; see @ref{Symbol tables}). For
+@code{n_strx} field is zero; see @ref{Symbol Tables}). For
@code{.stabd}, the @var{value} field is implicit and has the value of
the current file location. For @code{.stabx}, the @var{sdb-type} field
-is unused for stabs and can always be set to zero.
+is unused for stabs and can always be set to zero. The @var{other}
+field is almost always unused and can be set to zero.
The number in the @var{type} field gives some basic information about
which type of stab this is (or whether it @emph{is} a stab, as opposed
to an ordinary symbol). Each valid type number defines a different stab
type; further, the stab type defines the exact interpretation of, and
possible values for, any remaining @var{string}, @var{desc}, or
-@var{value} fields present in the stab. @xref{Stab types}, for a list
+@var{value} fields present in the stab. @xref{Stab Types}, for a list
in numeric order of the valid @var{type} field values for stab directives.
-@node String field
-@section The @code{.stabs} @var{string} field
+@node String Field
+@section The String Field
-For @code{.stabs} the @var{string} field holds the meat of the
-debugging information. The generally unstructured nature of this field
-is what makes stabs extensible. For some stab types the @var{string} field
+For most stabs the string field holds the meat of the
+debugging information. The flexible nature of this field
+is what makes stabs extensible. For some stab types the string field
contains only a name. For other stab types the contents can be a great
deal more complex.
-The overall format is of the @var{string} field is:
+The overall format of the string field for most stab types is:
@example
"@var{name}:@var{symbol-descriptor} @var{type-information}"
character that tells more specifically what kind of symbol the stab
represents. If the @var{symbol-descriptor} is omitted, but type
information follows, then the stab represents a local variable. For a
-list of symbol descriptors, see @ref{Symbol descriptors}. The @samp{c}
+list of symbol descriptors, see @ref{Symbol Descriptors}. The @samp{c}
symbol descriptor is an exception in that it is not followed by type
information. @xref{Constants}.
non-numeric then it is a @var{type-descriptor}, and tells what kind of
type is about to be defined. Any other values following the
@var{type-descriptor} vary, depending on the @var{type-descriptor}.
-@xref{Type descriptors}, for a list of @var{type-descriptor} values. If
+@xref{Type Descriptors}, for a list of @var{type-descriptor} values. If
a number follows the @samp{=} then the number is a @var{type-reference}.
For a full description of types, @ref{Types}.
expense of speed.
@end table
-All of this can make the @var{string} field quite long. All
+All of this can make the string field quite long. All
versions of GDB, and some versions of dbx, can handle arbitrarily long
strings. But many versions of dbx cretinously limit the strings to
about 80 characters, so compilers which must work with such dbx's need
to split the @code{.stabs} directive into several @code{.stabs}
directives. Each stab duplicates exactly all but the
-@var{string} field. The @var{string} field of
+string field. The string field of
every stab except the last is marked as continued with a
double-backslash at the end. Removing the backslashes and concatenating
-the @var{string} fields of each stab produces the original,
+the string fields of each stab produces the original,
long string.
-@node C example
-@section A simple example in C source
+@node C Example
+@section A Simple Example in C Source
To get the flavor of how stabs describe source information for a C
program, let's look at the simple program:
to parts of the @file{.s} file in the description of the stabs that
follows.
-@node Assembly code
-@section The simple example at the assembly level
+@node Assembly Code
+@section The Simple Example at the Assembly Level
This simple ``hello world'' example demonstrates several of the stab
types used to describe C language source files.
52 .stabn 224,0,0,LBE2
@end example
-@node Program structure
-@chapter Encoding the structure of the program
+@node Program Structure
+@chapter Encoding the Structure of the Program
The elements of the program structure that stabs encode include the name
of the main function, the names of the source and include files, the
blocks of code.
@menu
-* Main program:: Indicate what the main program is
-* Source files:: The path and name of the source file
-* Include files:: Names of include files
-* Line numbers::
+* Main Program:: Indicate what the main program is
+* Source Files:: The path and name of the source file
+* Include Files:: Names of include files
+* Line Numbers::
* Procedures::
-* Nested procedures::
-* Block structure::
+* Nested Procedures::
+* Block Structure::
@end menu
-@node Main program
-@section Main program
+@node Main Program
+@section Main Program
-@deffn @code{.stabs} N_MAIN
@findex N_MAIN
Most languages allow the main program to have any name. The
@code{N_MAIN} stab type tells the debugger the name that is used in this
-program. Only the @var{string} field is significant; it is the name of
+program. Only the string field is significant; it is the name of
a function which is the main program. Most C compilers do not use this
stab (they expect the debugger to assume that the name is @code{main}),
but some C compilers emit an @code{N_MAIN} stab for the @code{main}
function.
-@end deffn
-@node Source files
-@section Paths and names of the source files
+@node Source Files
+@section Paths and Names of the Source Files
-@deffn @code{.stabs} N_SO
@findex N_SO
Before any other stabs occur, there must be a stab specifying the source
file. This information is contained in a symbol of stab type
-@code{N_SO}; the @var{string} field contains the name of the file. The
-@var{value} of the symbol is the start address of the portion of the
+@code{N_SO}; the string field contains the name of the file. The
+value of the symbol is the start address of the portion of the
text section corresponding to that file.
-With the Sun Solaris2 compiler, the @var{desc} field contains a
+With the Sun Solaris2 compiler, the desc field contains a
source-language code.
@c Do the debuggers use it? What are the codes? -djm
.text
Ltext0:
@end example
-@end deffn
Instead of @code{N_SO} symbols, XCOFF uses a @code{.file} assembler
directive which assembles to a standard COFF @code{.file} symbol;
explaining this in detail is outside the scope of this document.
-@node Include files
-@section Names of include files
+@node Include Files
+@section Names of Include Files
There are several schemes for dealing with include files: the
traditional @code{N_SOL} approach, Sun's @code{N_BINCL} approach, and the
XCOFF @code{C_BINCL} approach (which despite the similar name has little in
common with @code{N_BINCL}).
-@deffn @code{.stabs} N_SOL
@findex N_SOL
An @code{N_SOL} symbol specifies which include file subsequent symbols
-refer to. The @var{string} field is the name of the file and the
-@var{value} is the text address corresponding to the start of the
+refer to. The string field is the name of the file and the
+value is the text address corresponding to the start of the
previous include file and the start of this one. To specify the main
source file again, use an @code{N_SOL} symbol with the name of the main
source file.
-@end deffn
-@deffn @code{.stabs} N_BINCL
-@deffnx @code{.stabs} N_EINCL
-@deffnx {} N_EXCL
@findex N_BINCL
@findex N_EINCL
@findex N_EXCL
-On Suns, an @code{N_BINCL} symbol specifies the start of an include file.
-In an object file, only the @var{string} is significant; the Sun linker
-puts data into some of the other fields. The end of the include file is
-marked by an @code{N_EINCL} symbol (which has no @var{string} field). In
-an object file, there is no significant data in the @code{N_EINCL}
-symbol; the Sun linker puts data into some of the fields.
-@code{N_BINCL} and @code{N_EINCL} can be nested.
-
-If the linker detects that two source files have identical stabs with an
-@code{N_BINCL} and @code{N_EINCL} pair (as will generally be the case
+The @code{N_BINCL} approach works as follows. An @code{N_BINCL} symbol
+specifies the start of an include file. In an object file, only the
+string is significant; the Sun linker puts data into some of the
+other fields. The end of the include file is marked by an
+@code{N_EINCL} symbol (which has no string field). In an object
+file, there is no significant data in the @code{N_EINCL} symbol; the Sun
+linker puts data into some of the fields. @code{N_BINCL} and
+@code{N_EINCL} can be nested.
+
+If the linker detects that two source files have identical stabs between
+an @code{N_BINCL} and @code{N_EINCL} pair (as will generally be the case
for a header file), then it only puts out the stabs once. Each
additional occurance is replaced by an @code{N_EXCL} symbol. I believe
the Sun (SunOS4, not sure about Solaris) linker is the only one which
supports this feature.
@c What do the fields of N_EXCL contain? -djm
-@end deffn
-@deffn @code{.bi} C_BINCL
-@deffnx @code{.ei} C_EINCL
@findex C_BINCL
@findex C_EINCL
For the start of an include file in XCOFF, use the @file{.bi} assembler
directive, which generates a @code{C_BINCL} symbol. A @file{.ei}
directive, which generates a @code{C_EINCL} symbol, denotes the end of
the include file. Both directives are followed by the name of the
-source file in quotes, which becomes the @var{string} for the symbol.
-The @var{value} of each symbol, produced automatically by the assembler
+source file in quotes, which becomes the string for the symbol.
+The value of each symbol, produced automatically by the assembler
and linker, is the offset into the executable of the beginning
(inclusive, as you'd expect) or end (inclusive, as you would not expect)
of the portion of the COFF line table that corresponds to this include
file. @code{C_BINCL} and @code{C_EINCL} do not nest.
-@end deffn
-@node Line numbers
-@section Line numbers
+@node Line Numbers
+@section Line Numbers
-@deffn @code{.stabn} N_SLINE
@findex N_SLINE
An @code{N_SLINE} symbol represents the start of a source line. The
-@var{desc} field contains the line number and the @var{value} field
+desc field contains the line number and the value
contains the code address for the start of that source line. On most
machines the address is absolute; for Sun's stabs-in-ELF, it is relative
to the function in which the @code{N_SLINE} symbol occurs.
-@end deffn
-@deffn @code{.stabn} N_DSLINE
-@deffnx @code{.stabn} N_BSLINE
@findex N_DSLINE
@findex N_BSLINE
GNU documents @code{N_DSLINE} and @code{N_BSLINE} symbols for line
to @code{N_SLINE} but are relocated differently by the linker. They
were intended to be used to describe the source location of a variable
declaration, but I believe that GCC2 actually puts the line number in
-the @var{desc} field of the stab for the variable itself. GDB has been
-ignoring these symbols (unless they contain a @var{string} field) since
+the desc field of the stab for the variable itself. GDB has been
+ignoring these symbols (unless they contain a string field) since
at least GDB 3.5.
-@end deffn
For single source lines that generate discontiguous code, such as flow
of control statements, there may be more than one line number entry for
the same source line. In this case there is a line number entry at the
start of each code range, each with the same line number.
-XCOFF uses COFF line numbers, which are outside the scope of this
-document.
+XCOFF does not use stabs for line numbers. Instead, it uses COFF line
+numbers (which are outside the scope of this document). Standard COFF
+line numbers cannot deal with include files, but in XCOFF this is fixed
+with the C_BINCL method of marking include files (@pxref{Include
+Files}).
@node Procedures
@section Procedures
-@deffn @code{.stabs} N_FUN
@findex N_FUN
-All of the following stabs use the @code{N_FUN} symbol type.
+@findex N_FNAME
+@findex N_STSYM, for functions (Sun acc)
+@findex N_GSYM, for functions (Sun acc)
+All of the following stabs normally use the @code{N_FUN} symbol type.
+However, Sun's @code{acc} compiler on SunOS4 uses @code{N_GSYM} and
+@code{N_STSYM}, which means that the value of the stab for the function
+is useless and the debugger must get the address of the function from
+the non-stab symbols instead. BSD Fortran is said to use @code{N_FNAME}
+with the same restriction; the value of the symbol is not useful (I'm
+not sure it really does use this, because GDB doesn't handle this and no
+one has complained).
A function is represented by an @samp{F} symbol descriptor for a global
-(extern) function, and @samp{f} for a static (local) function. (The next
-@code{N_SLINE} symbol gives the line number of the start
-of the function.) The @var{value} field is the address of the start of the
-function (absolute for @code{a.out}; relative to the start of the file
-for Sun's stabs-in-ELF). The type information of the stab represents
-the return type of the function; thus @samp{foo:f5} means that foo is a
-function returning type 5.
-
-@c What determines whether the option here v is taken? -djm
-The type information of the stab is optionally followed by type
-information for each argument, with each argument preceded by @samp{;}.
-An argument type of 0 means that additional arguments are being passed,
-whose types and number may vary (@samp{...} in ANSI C). This extension
-is used by Sun's Solaris compiler. GDB has tolerated it (parsed the
-syntax, if not necessarily used the information) since at least version
-4.8; I don't know whether all versions of dbx tolerate it. The
-argument types given here are not redundant with the symbols for the
-arguments themselves (@pxref{Parameters}); they are the types of the
-arguments as they are passed, before any conversions might take place.
-For example, if a C function which is declared without a prototype takes
-a @code{float} argument, the value is passed as a @code{double} but then
-converted to a @code{float}. Debuggers need to use the types given in
-the arguments when printing values, but if calling the function they
-need to use the types given in the symbol defining the function.
-@c Are the "arguments themselves" referred to above the actual
-@c or formal parameters? I'm confused. -djm
+(extern) function, and @samp{f} for a static (local) function. The
+value is the address of the start of the function (absolute
+for @code{a.out}; relative to the start of the file for Sun's
+stabs-in-ELF). The type information of the stab represents the return
+type of the function; thus @samp{foo:f5} means that foo is a function
+returning type 5. There is no need to try to get the line number of the
+start of the function from the stab for the function; it is in the next
+@code{N_SLINE} symbol.
+
+@c FIXME: verify whether the "I suspect" below is true or not.
+Some compilers (such as Sun's Solaris compiler) support an extension for
+specifying the types of the arguments. I suspect this extension is not
+used for old (non-prototyped) function definitions in C. If the
+extension is in use, the type information of the stab for the function
+is followed by type information for each argument, with each argument
+preceded by @samp{;}. An argument type of 0 means that additional
+arguments are being passed, whose types and number may vary (@samp{...}
+in ANSI C). GDB has tolerated this extension (parsed the syntax, if not
+necessarily used the information) since at least version 4.8; I don't
+know whether all versions of dbx tolerate it. The argument types given
+here are not redundant with the symbols for the formal parameters
+(@pxref{Parameters}); they are the types of the arguments as they are
+passed, before any conversions might take place. For example, if a C
+function which is declared without a prototype takes a @code{float}
+argument, the value is passed as a @code{double} but then converted to a
+@code{float}. Debuggers need to use the types given in the arguments
+when printing values, but when calling the function they need to use the
+types given in the symbol defining the function.
If the return type and types of arguments of a function which is defined
in another source file are specified (i.e., a function prototype in ANSI
type of the function, followed by the arguments, each preceded by
@samp{;}, as in a stab with symbol descriptor @samp{f} or @samp{F}.
This use of symbol descriptor @samp{P} can be distinguished from its use
-for register parameters (@pxref{Register parameters}) by the fact that it has
+for register parameters (@pxref{Register Parameters}) by the fact that it has
symbol type @code{N_FUN}.
The AIX documentation also defines symbol descriptor @samp{J} as an
These symbol descriptors are unusual in that they are not followed by
type information.
-Here is an exploded summary (with whitespace added for clarity):
-
-@example
-.stabs "@var{name}:
- @var{desc} @r{(global proc @samp{F})}
- @var{return_type_ref} @r{(int)}
- ",N_FUN, NIL, NIL,
- @var{address}
-@end example
-
-Going back to our ``hello world'' example program,
-
-@example
-48 ret
-49 restore
-@end example
-
-@noindent
-The @code{.stabs} entry after this code fragment shows the @var{name} of
-the procedure (@code{main}); the type descriptor @var{desc} (@code{F},
-for a global procedure); a reference to the predefined type @code{int}
-for the return type; and the starting @var{address} of the procedure.
+The following example shows a stab for a function @code{main} which
+returns type number @code{1}. The @code{_main} specified for the value
+is a reference to an assembler label which is used to fill in the start
+address of the function.
@example
-50 .stabs "main:F1",36,0,0,_main
+.stabs "main:F1",36,0,0,_main # @r{36 is N_FUN}
@end example
The stab representing a procedure is located immediately following the
group of other stabs describing elements of the procedure. These other
stabs describe the procedure's parameters, its block local variables, and
its block structure.
-@end deffn
-@node Nested procedures
-@section Nested procedures
+@node Nested Procedures
+@section Nested Procedures
-For any of the @code{N_FUN} symbol descriptors, after the symbol
-descriptor and the type information is optionally a scope specifier.
-This consists of a comma, the name of the procedure, another comma, and
-the name of the enclosing procedure. The first name is local to the
-scope specified, and seems to be redundant with the name of the symbol
-(before the @samp{:}). This feature is used by GCC, and presumably
-Pascal, Modula-2, etc., compilers, for nested functions.
+For any of the symbol descriptors representing procedures, after the
+symbol descriptor and the type information is optionally a scope
+specifier. This consists of a comma, the name of the procedure, another
+comma, and the name of the enclosing procedure. The first name is local
+to the scope specified, and seems to be redundant with the name of the
+symbol (before the @samp{:}). This feature is used by GCC, and
+presumably Pascal, Modula-2, etc., compilers, for nested functions.
If procedures are nested more than one level deep, only the immediately
containing scope is specified. For example, this code:
.stabs "foo:F1",36,0,0,_foo
@end example
-@node Block structure
-@section Block structure
+@node Block Structure
+@section Block Structure
-@deffn @code{.stabn} N_LBRAC
-@deffnx @code{.stabn} N_RBRAC
@findex N_LBRAC
@findex N_RBRAC
The program's block structure is represented by the @code{N_LBRAC} (left
defined inside a block precede the @code{N_LBRAC} symbol for most
compilers, including GCC. Other compilers, such as the Convex, Acorn
RISC machine, and Sun @code{acc} compilers, put the variables after the
-@code{N_LBRAC} symbol. The @var{value} fields of the @code{N_LBRAC} and
+@code{N_LBRAC} symbol. The values of the @code{N_LBRAC} and
@code{N_RBRAC} symbols are the start and end addresses of the code of
the block, respectively. For most machines, they are relative to the
starting address of this source file. For the Gould NP1, they are
scope of a procedure are located after the @code{N_FUN} stab that
represents the procedure itself.
-Sun documents the @var{desc} field of @code{N_LBRAC} and
+Sun documents the desc field of @code{N_LBRAC} and
@code{N_RBRAC} symbols as containing the nesting level of the block.
-However, dbx seems to not care, and GCC always sets @var{desc} to
+However, dbx seems to not care, and GCC always sets desc to
zero.
-@end deffn
@node Constants
@chapter Constants
@item e @var{type-information} , @var{value}
Constant whose value can be represented as integral.
@var{type-information} is the type of the constant, as it would appear
-after a symbol descriptor (@pxref{String field}). @var{value} is the
+after a symbol descriptor (@pxref{String Field}). @var{value} is the
numeric value of the constant. GDB 4.9 does not actually get the right
value if @var{value} does not fit in a host @code{int}, but it does not
do anything violent, and future debuggers could be extended to accept
@item S @var{type-information} , @var{elements} , @var{bits} , @var{pattern}
Set constant. @var{type-information} is the type of the constant, as it
-would appear after a symbol descriptor (@pxref{String field}).
+would appear after a symbol descriptor (@pxref{String Field}).
@var{elements} is the number of elements in the set (does this means
how many bits of @var{pattern} are actually used, which would be
redundant with the type, or perhaps the number of bits set in
statically, or as arguments to a function.
@menu
-* Stack variables:: Variables allocated on the stack.
-* Global variables:: Variables used by more than one source file.
-* Register variables:: Variables in registers.
-* Common blocks:: Variables statically allocated together.
+* Stack Variables:: Variables allocated on the stack.
+* Global Variables:: Variables used by more than one source file.
+* Register Variables:: Variables in registers.
+* Common Blocks:: Variables statically allocated together.
* Statics:: Variables local to one source file.
* Parameters:: Variables for arguments to functions.
@end menu
-@node Stack variables
-@section Automatic variables allocated on the stack
+@node Stack Variables
+@section Automatic Variables Allocated on the Stack
If a variable's scope is local to a function and its lifetime is only as
long as that function executes (C calls such variables
@dfn{automatic}), it can be allocated in a register (@pxref{Register
-variables}) or on the stack.
+Variables}) or on the stack.
-@deffn @code{.stabs} N_LSYM
@findex N_LSYM
-Each variable allocated on the stack has a stab of type @code{N_LSYM},
-with the symbol descriptor omitted. Since type information should begin
-with a digit, @samp{-}, or @samp{(}, only those characters precluded
-from being used for symbol descriptors. However, the Acorn RISC machine
-(ARM) is said to get this wrong: it puts out a mere type definition
-here, without the preceding @samp{@var{type-number}=}. This is a bad
-idea; there is no guarantee that type descriptors are distinct from
-symbol descriptors.
-
-The @var{value} of the stab is the offset of the variable within the
+Each variable allocated on the stack has a stab with the symbol
+descriptor omitted. Since type information should begin with a digit,
+@samp{-}, or @samp{(}, only those characters precluded from being used
+for symbol descriptors. However, the Acorn RISC machine (ARM) is said
+to get this wrong: it puts out a mere type definition here, without the
+preceding @samp{@var{type-number}=}. This is a bad idea; there is no
+guarantee that type descriptors are distinct from symbol descriptors.
+Stabs for stack variables use the @code{N_LSYM} stab type.
+
+The value of the stab is the offset of the variable within the
local variables. On most machines this is an offset from the frame
pointer and is negative. The location of the stab specifies which block
-it is defined in; see @ref{Block structure}.
+it is defined in; see @ref{Block Structure}.
For example, the following C code:
@end example
@xref{Procedures} for more information on the @code{N_FUN} stab, and
-@ref{Block structure} for more information on the @code{N_LBRAC} and
+@ref{Block Structure} for more information on the @code{N_LBRAC} and
@code{N_RBRAC} stabs.
-@end deffn
-@node Global variables
-@section Global variables
+@node Global Variables
+@section Global Variables
-@deffn @code{.stabs} N_GSYM
@findex N_GSYM
A variable whose scope is not specific to just one source file is
represented by the @samp{G} symbol descriptor. These stabs use the
@code{N_GSYM} stab type. The type information for the stab
-(@pxref{String field}) gives the type of the variable.
+(@pxref{String Field}) gives the type of the variable.
For example, the following source code:
from the external symbol for the global variable. In the example above,
the @code{.global _g_foo} and @code{_g_foo:} lines tell the assembler to
produce an external symbol.
-@end deffn
-@node Register variables
-@section Register variables
+@node Register Variables
+@section Register Variables
-@deffn @code{.stabn} N_RSYM
@findex N_RSYM
@c According to an old version of this manual, AIX uses C_RPSYM instead
@c of C_RSYM. I am skeptical; this should be verified.
Register variables have their own stab type, @code{N_RSYM}, and their
-own symbol descriptor, @samp{r}. The stab's @var{value} field contains the
+own symbol descriptor, @samp{r}. The stab's value is the
number of the register where the variable data will be stored.
@c .stabs "name:type",N_RSYM,0,RegSize,RegNumber (Sun doc)
@noindent
then the stab may be emitted at the end of the object file, with
the other bss symbols.
-@end deffn
-@node Common blocks
-@section Common blocks
+@node Common Blocks
+@section Common Blocks
A common block is a statically allocated section of memory which can be
referred to by several source files. It may contain several variables.
I believe Fortran is the only language with this feature.
-@deffn @code{.stabs} N_BCOMM
-@deffnx @code{.stabs} N_ECOMM
@findex N_BCOMM
@findex N_ECOMM
A @code{N_BCOMM} stab begins a common block and an @code{N_ECOMM} stab
ends it. The only field that is significant in these two stabs is the
-@var{string}, which names a normal (non-debugging) symbol that gives the
+string, which names a normal (non-debugging) symbol that gives the
address of the common block.
-@end deffn
-@deffn @code{.stabn} N_ECOML
@findex N_ECOML
Each stab between the @code{N_BCOMM} and the @code{N_ECOMM} specifies a
-member of that common block; its @var{value} is the offset within the
+member of that common block; its value is the offset within the
common block of that variable. The @code{N_ECOML} stab type is
documented for this purpose, but Sun's Fortran compiler uses
@code{N_GSYM} instead. The test case I looked at had a common block
local to a function and it used the @samp{V} symbol descriptor; I assume
one would use @samp{S} if not local to a function (that is, if a common
block @emph{can} be anything other than local to a function).
-@end deffn
@node Statics
-@section Static variables
+@section Static Variables
Initialized static variables are represented by the @samp{S} and
@samp{V} symbol descriptors. @samp{S} means file scope static, and
@c (although GCC
@c 2.4.5 has a bug in that it uses @code{N_FUN}, so neither dbx nor GDB can
@c find the variables)
-@deffn @code{.stabs} N_STSYM
-@deffnx @code{.stabs} N_LCSYM
@findex N_STSYM
@findex N_LCSYM
-In a.out files, @code{N_STSYM} means the data segment, @code{N_FUN}
-means the text segment, and @code{N_LCSYM} means the bss segment.
+In a.out files, @code{N_STSYM} means the data section, @code{N_FUN}
+means the text section, and @code{N_LCSYM} means the bss section. For
+those systems with a read-only data section separate from the text
+section (Solaris), @code{N_ROSYM} means the read-only data section.
For example, the source lines:
@dots{}
.stabs "var_noinit:S1",40,0,0,_var_noinit # @r{40 is N_LCSYM}
@end example
-@end deffn
In XCOFF files, each symbol has a section number, so the stab type
-need not indicate the segment.
+need not indicate the section.
In ECOFF files, the storage class is used to specify the section, so the
-stab type need not indicate the segment.
+stab type need not indicate the section.
-@c In ELF files, it apparently is a big mess. See kludge in dbxread.c
-@c in GDB. FIXME: Investigate where this kludge comes from.
-@c
-@c This is the place to mention N_ROSYM; I'd rather do so once I can
-@c coherently explain how this stuff works for stabs-in-ELF.
+In ELF files, for Solaris 2.1, symbol descriptor @samp{S} means that the
+address is absolute (ld relocates it) and symbol descriptor @samp{V}
+means that the address is relative to the start of the relevant section
+for that compilation unit. I don't know what it does for @samp{S} stabs
+on Solaris 2.3 (in which ld no longer relocates stabs). For more
+information on ld stab relocation, @xref{Stabs In ELF}.
@node Parameters
@section Parameters
-Actual parameters to a function are represented by a stab (or sometimes
+Formal parameters to a function are represented by a stab (or sometimes
two; see below) for each parameter. The stabs are in the order in which
the debugger should print the parameters (i.e., the order in which the
parameters are declared in the source file). The exact form of the stab
depends on how the parameter is being passed.
-@deffn @code{.stabs} N_PSYM
@findex N_PSYM
Parameters passed on the stack use the symbol descriptor @samp{p} and
-the @code{N_PSYM} symbol type. The @var{value} of the symbol is an offset
+the @code{N_PSYM} symbol type. The value of the symbol is an offset
used to locate the parameter on the stack; its exact meaning is
machine-dependent, but on most machines it is an offset from the frame
pointer.
The type definition of @code{argv} is interesting because it contains
several type definitions. Type 21 is pointer to type 2 (char) and
@code{argv} (type 20) is pointer to type 21.
-@end deffn
+
+@c FIXME: figure out what these mean and describe them coherently.
+The following symbol descriptors are also said to go with @code{N_PSYM}.
+The value of the symbol is said to be an offset from the argument
+pointer (I'm not sure whether this is true or not).
+
+@example
+pP (<<??>>)
+pF Fortran function parameter
+X (function result variable)
+b (based variable)
+@end example
@menu
-* Register parameters::
-* Local variable parameters::
-* Reference parameters::
-* Conformant arrays::
+* Register Parameters::
+* Local Variable Parameters::
+* Reference Parameters::
+* Conformant Arrays::
@end menu
-@node Register parameters
-@subsection Passing parameters in registers
+@node Register Parameters
+@subsection Passing Parameters in Registers
If the parameter is passed in a register, then traditionally there are
two symbols for each argument:
Debuggers use the second one to find the value, and the first one to
know that it is an argument.
-@deffn @code{.stabs} C_RPSYM
@findex C_RPSYM
+@findex N_RSYM, for parameters
Because that approach is kind of ugly, some compilers use symbol
descriptor @samp{P} or @samp{R} to indicate an argument which is in a
register. Symbol type @code{C_RPSYM} is used with @samp{R} and
-@code{N_RSYM} is used with @samp{P}. The symbol @var{value} field is
+@code{N_RSYM} is used with @samp{P}. The symbol's value is
the register number. @samp{P} and @samp{R} mean the same thing; the
difference is that @samp{P} is a GNU invention and @samp{R} is an IBM
(XCOFF) invention. As of version 4.9, GDB should handle either one.
-@end deffn
There is at least one case where GCC uses a @samp{p} and @samp{r} pair
rather than @samp{P}; this is where the argument is passed in the
indicates that it's a floating point register? I haven't verified
whether the system actually does what the documentation indicates.
+@c FIXME: On the hppa this is for any type > 8 bytes, I think, and not
+@c for small structures (investigate).
On the sparc and hppa, for a @samp{P} symbol whose type is a structure
or union, the register contains the address of the structure. On the
sparc, this is also true of a @samp{p} and @samp{r} pair (using Sun
access"; I don't know the source for this information), but I don't know
details or what compilers or debuggers use it, if any (not GDB or GCC).
It is not clear to me whether this case needs to be dealt with
-differently than parameters passed by reference (@pxref{Reference parameters}).
+differently than parameters passed by reference (@pxref{Reference Parameters}).
-@node Local variable parameters
-@subsection Storing parameters as local variables
+@node Local Variable Parameters
+@subsection Storing Parameters as Local Variables
There is a case similar to an argument in a register, which is an
argument that is actually stored as a local variable. Sometimes this
stores it as a local variable. If possible, the compiler should claim
that it's in a register, but this isn't always done.
+@findex N_LSYM, for parameter
Some compilers use the pair of symbols approach described above
(@samp{@var{arg}:p} followed by @samp{@var{arg}:}); this includes GCC1
(not GCC2) on the sparc when passing a small structure and GCC2
(sometimes) when the argument type is @code{float} and it is passed as a
@code{double} and converted to @code{float} by the prologue (in the
latter case the type of the @samp{@var{arg}:p} symbol is @code{double}
-and the type of the @samp{@var{arg}:} symbol is @code{float}). GCC, at
-least on the 960, uses a single @samp{p} symbol descriptor for an
-argument which is stored as a local variable but uses @code{N_LSYM}
-instead of @code{N_PSYM}. In this case, the @var{value} of the symbol
-is an offset relative to the local variables for that function, not
-relative to the arguments; on some machines those are the same thing,
-but not on all.
+and the type of the @samp{@var{arg}:} symbol is @code{float}).
+
+GCC, at least on the 960, has another solution to the same problem. It
+uses a single @samp{p} symbol descriptor for an argument which is stored
+as a local variable but uses @code{N_LSYM} instead of @code{N_PSYM}. In
+this case, the value of the symbol is an offset relative to the local
+variables for that function, not relative to the arguments; on some
+machines those are the same thing, but not on all.
+
+@c This is mostly just background info; the part that logically belongs
+@c here is the last sentence.
+On the VAX or on other machines in which the calling convention includes
+the number of words of arguments actually passed, the debugger (GDB at
+least) uses the parameter symbols to keep track of whether it needs to
+print nameless arguments in addition to the formal parameters which it
+has printed because each one has a stab. For example, in
+
+@example
+extern int fprintf (FILE *stream, char *format, @dots{});
+@dots{}
+fprintf (stdout, "%d\n", x);
+@end example
-@node Reference parameters
-@subsection Passing parameters by reference
+there are stabs for @code{stream} and @code{format}. On most machines,
+the debugger can only print those two arguments (because it has no way
+of knowing that additional arguments were passed), but on the VAX or
+other machines with a calling convention which indicates the number of
+words of arguments, the debugger can print all three arguments. To do
+so, the parameter symbol (symbol descriptor @samp{p}) (not necessarily
+@samp{r} or symbol descriptor omitted symbols) needs to contain the
+actual type as passed (for example, @code{double} not @code{float} if it
+is passed as a double and converted to a float).
+
+@node Reference Parameters
+@subsection Passing Parameters by Reference
If the parameter is passed by reference (e.g., Pascal @code{VAR}
parameters), then the symbol descriptor is @samp{v} if it is in the
respectively. I believe @samp{a} is an AIX invention; @samp{v} is
supported by all stabs-using systems as far as I know.
-@node Conformant arrays
-@subsection Passing conformant array parameters
+@node Conformant Arrays
+@subsection Passing Conformant Array Parameters
@c Is this paragraph correct? It is based on piecing together patchy
@c information and some guesswork
languages, in which the size of an array parameter is not known to the
called function until run-time. Such parameters have two stabs: a
@samp{x} for the array itself, and a @samp{C}, which represents the size
-of the array. The @var{value} of the @samp{x} stab is the offset in the
+of the array. The value of the @samp{x} stab is the offset in the
argument list where the address of the array is stored (it this right?
-it is a guess); the @var{value} of the @samp{C} stab is the offset in the
+it is a guess); the value of the @samp{C} stab is the offset in the
argument list where the size of the array (in elements? in bytes?) is
stored.
@node Types
-@chapter Defining types
+@chapter Defining Types
The examples so far have described types as references to previously
defined types, or defined in terms of subranges of or pointers to
descriptors that may follow the @samp{=} in a type definition.
@menu
-* Builtin types:: Integers, floating point, void, etc.
-* Miscellaneous types:: Pointers, sets, files, etc.
-* Cross-references:: Referring to a type not yet defined.
+* Builtin Types:: Integers, floating point, void, etc.
+* Miscellaneous Types:: Pointers, sets, files, etc.
+* Cross-References:: Referring to a type not yet defined.
* Subranges:: A type with a specific range.
* Arrays:: An aggregate type of same-typed elements.
* Strings:: Like an array but also has a length.
* Structures:: An aggregate type of different-typed elements.
* Typedefs:: Giving a type a name.
* Unions:: Different types sharing storage.
-* Function types::
+* Function Types::
@end menu
-@node Builtin types
-@section Builtin types
+@node Builtin Types
+@section Builtin Types
Certain types are built in (@code{int}, @code{short}, @code{void},
@code{float}, etc.); the debugger recognizes these types and knows how
formats. The following sections describe each of these formats.
@menu
-* Traditional builtin types:: Put on your seatbelts and prepare for kludgery
-* Builtin type descriptors:: Builtin types with special type descriptors
-* Negative type numbers:: Builtin types using negative type numbers
+* Traditional Builtin Types:: Put on your seatbelts and prepare for kludgery
+* Builtin Type Descriptors:: Builtin types with special type descriptors
+* Negative Type Numbers:: Builtin types using negative type numbers
@end menu
-@node Traditional builtin types
-@subsection Traditional builtin types
+@node Traditional Builtin Types
+@subsection Traditional Builtin Types
This is the traditional, convoluted method for defining builtin types.
There are several classes of such type definitions: integer, floating
point, and @code{void}.
@menu
-* Traditional integer types::
-* Traditional other types::
+* Traditional Integer Types::
+* Traditional Other Types::
@end menu
-@node Traditional integer types
-@subsubsection Traditional integer types
+@node Traditional Integer Types
+@subsubsection Traditional Integer Types
Often types are defined as subranges of themselves. If the bounding values
fit within an @code{int}, then they are given normally. For example:
big to describe in an @code{int}. Traditionally this is only used for
@code{unsigned int} and @code{unsigned long}:
-@c FIXME: Update this for the 2.4.5 output, not 2.3.3
@example
.stabs "unsigned int:t4=r1;0;-1;",128,0,0,0
-.stabs "long long int:t7=r1;0;-1;",128,0,0,0
@end example
-For larger types, GCC
-2.4.5 puts out bounds in octal, with a leading 0. In this case a
-negative bound consists of a number which is a 1 bit followed by a bunch
-of 0 bits, and a positive bound is one in which a bunch of bits are 1.
-All known versions of dbx and GDB version 4 accept this, but GDB 3.5
-refuses to read the whole file containing such symbols. So GCC 2.3.3
-did not output the proper size for these types.
+For larger types, GCC 2.4.5 puts out bounds in octal, with a leading 0.
+In this case a negative bound consists of a number which is a 1 bit
+followed by a bunch of 0 bits, and a positive bound is one in which a
+bunch of bits are 1. All known versions of dbx and GDB version 4 accept
+this, but GDB 3.5 refuses to read the whole file containing such
+symbols. So GCC 2.3.3 did not output the proper size for these types.
+@c FIXME: How about an example?
If the lower bound of a subrange is 0 and the upper bound is negative,
the type is an unsigned integral type whose size in bytes is the
subrange, the type should be a subrange of itself. I'm not sure whether
this is the case for Convex.
-@node Traditional other types
-@subsubsection Traditional other types
+@node Traditional Other Types
+@subsubsection Traditional Other Types
If the upper bound of a subrange is 0 and the lower bound is positive,
the type is a floating point type, and the lower bound of the subrange
I'm not sure how a boolean type is represented.
-@node Builtin type descriptors
-@subsection Defining builtin types using builtin type descriptors
+@node Builtin Type Descriptors
+@subsection Defining Builtin Types Using Builtin Type Descriptors
This is the method used by Sun's @code{acc} for defining builtin types.
These are the type descriptors to define builtin types:
of bits in the type.
Note that type descriptor @samp{b} used for builtin types conflicts with
-its use for Pascal space types (@pxref{Miscellaneous types}); they can
+its use for Pascal space types (@pxref{Miscellaneous Types}); they can
be distinguished because the character following the type descriptor
will be a digit, @samp{(}, or @samp{-} for a Pascal space type, or
@samp{u} or @samp{s} for a builtin type.
@item w
Documented by AIX to define a wide character type, but their compiler
-actually uses negative type numbers (@pxref{Negative type numbers}).
+actually uses negative type numbers (@pxref{Negative Type Numbers}).
@item R @var{fp-type} ; @var{bytes} ;
Define a floating point type. @var{fp-type} has one of the following values:
precision? Double precison?).
@item 6 (NF_LDOUBLE)
-@code{long double}. This should probably only be used for Sun format
+Long double. This should probably only be used for Sun format
@code{long double}, and new codes should be used for other floating
point formats (@code{NF_DOUBLE} can be used if a @code{long double} is
really just an IEEE double, of course).
@item g @var{type-information} ; @var{nbits}
Documented by AIX to define a floating type, but their compiler actually
-uses negative type numbers (@pxref{Negative type numbers}).
+uses negative type numbers (@pxref{Negative Type Numbers}).
@item c @var{type-information} ; @var{nbits}
Documented by AIX to define a complex type, but their compiler actually
-uses negative type numbers (@pxref{Negative type numbers}).
+uses negative type numbers (@pxref{Negative Type Numbers}).
@end table
The C @code{void} type is defined as a signed integral type 0 bits long:
I'm not sure how a boolean type is represented.
-@node Negative type numbers
-@subsection Negative type numbers
+@node Negative Type Numbers
+@subsection Negative Type Numbers
This is the method used in XCOFF for defining builtin types.
Since the debugger knows about the builtin types anyway, the idea of
Unicode?).
@end table
-@node Miscellaneous types
-@section Miscellaneous types
-
-These type descriptors are for types that are built into languages and
-are derived from the fundamental types.
+@node Miscellaneous Types
+@section Miscellaneous Types
@table @code
@item b @var{type-information} ; @var{bytes}
Pascal space type. This is documented by IBM; what does it mean?
This use of the @samp{b} type descriptor can be distinguished
-from its use for builtin integral types (@pxref{Builtin type
-descriptors}) because the character following the type descriptor is
+from its use for builtin integral types (@pxref{Builtin Type
+Descriptors}) because the character following the type descriptor is
always a digit, @samp{(}, or @samp{-}.
@item B @var{type-information}
-A @code{volatile}-qualified version of @var{type-information}. This is
+A volatile-qualified version of @var{type-information}. This is
a Sun extension. References and stores to a variable with a
-@code{volatile}-qualified type must not be optimized or cached; they
+volatile-qualified type must not be optimized or cached; they
must occur as the user specifies them.
@item d @var{type-information}
by Pascal.
@item k @var{type-information}
-A @code{const}-qualified version of @var{type-information}. This is a
-Sun extension. A variable with a @code{const}-qualified type cannot be
-modified.
+A const-qualified version of @var{type-information}. This is a Sun
+extension. A variable with a const-qualified type cannot be modified.
@item M @var{type-information} ; @var{length}
Multiple instance type. The type seems to composed of @var{length}
repetitions of @var{type-information}, for example @code{character*3} is
represented by @samp{M-2;3}, where @samp{-2} is a reference to a
-character type (@pxref{Negative type numbers}). I'm not sure how this
+character type (@pxref{Negative Type Numbers}). I'm not sure how this
differs from an array. This appears to be a Fortran feature.
@var{length} is a bound, like those in range types; see @ref{Subranges}.
Pointer to @var{type-information}.
@end table
-@node Cross-references
-@section Cross-references to other types
+@node Cross-References
+@section Cross-References to Other Types
A type can be used before it is defined; one common way to deal with
that situation is just to use a type reference to a type which has not
that it identifies the module; I don't understand whether the name of
the type given here is always just the same as the name we are giving
it, or whether this type descriptor is used with a nameless stab
-(@pxref{String field}), or what. The symbol ends with @samp{;}.
+(@pxref{String Field}), or what. The symbol ends with @samp{;}.
@node Subranges
-@section Subrange types
+@section Subrange Types
The @samp{r} type descriptor defines a type as a subrange of another
type. It is followed by type information for the type of which it is a
There is no bound.
@end table
-Subranges are also used for builtin types; see @ref{Traditional builtin types}.
+Subranges are also used for builtin types; see @ref{Traditional Builtin Types}.
@node Arrays
-@section Array types
+@section Array Types
Arrays use the @samp{a} type descriptor. Following the type descriptor
is the type of the index and the type of the array elements. If the
It is well established, and widely used, that the type of the index,
unlike most types found in the stabs, is merely a type definition, not
-type information (@pxref{String field}) (that is, it need not start with
+type information (@pxref{String Field}) (that is, it need not start with
@samp{@var{type-number}=} if it is defining a new type). According to a
comment in GDB, this is also true of the type of the array elements; it
gives @samp{ar1;1;10;ar1;1;10;4} as a legitimate way to express a two
dimensional array. According to AIX documentation, the element type
must be type information. GDB accepts either.
-The type of the index is often a range type, expressed as the letter @samp{r}
-and some parameters. It defines the size of the array. In the example
-below, the range @samp{r1;0;2;} defines an index type which is a
-subrange of type 1 (integer), with a lower bound of 0 and an upper bound
-of 2. This defines the valid range of subscripts of a three-element C
-array.
+The type of the index is often a range type, expressed as the type
+descriptor @samp{r} and some parameters. It defines the size of the
+array. In the example below, the range @samp{r1;0;2;} defines an index
+type which is a subrange of type 1 (integer), with a lower bound of 0
+and an upper bound of 2. This defines the valid range of subscripts of
+a three-element C array.
For example, the definition:
example, an array of 3-byte objects might, if unpacked, have each
element aligned on a 4-byte boundary, but if packed, have no padding.
One way to specify that something is packed is with type attributes
-(@pxref{String field}). In the case of arrays, another is to use the
+(@pxref{String Field}). In the case of arrays, another is to use the
@samp{P} type descriptor instead of @samp{a}. Other than specifying a
packed array, @samp{P} is identical to @samp{a}.
following the @samp{22=} of the type definition narrows it down to an
enumeration type. Following the @samp{e} is a list of the elements of
the enumeration. The format is @samp{@var{name}:@var{value},}. The
-list of elements ends with a @samp{;}.
+list of elements ends with @samp{;}.
There is no standard way to specify the size of an enumeration type; it
is determined by the architecture (normally all enumerations types are
32 bits). There should be a way to specify an enumeration type of
another size; type attributes would be one way to do this. @xref{Stabs
-format}.
+Format}.
@node Structures
@section Structures
The structure tag has an @code{N_LSYM} stab type because, like the
enumeration, the symbol has file scope. Like the enumeration, the
symbol descriptor is @samp{T}, for enumeration, structure, or tag type.
-The symbol descriptor @samp{s} following the @samp{16=} of the type
+The type descriptor @samp{s} following the @samp{16=} of the type
definition narrows the symbol type to structure.
-Following the structure symbol descriptor is the number of bytes the
+Following the @samp{s} type descriptor is the number of bytes the
structure occupies, followed by a description of each structure element.
The structure element descriptions are of the form @var{name:type, bit
offset from the start of the struct, number of bits in the element}.
-@display
-.stabs "name:sym_desc(struct tag) Type_def(16)=type_desc(struct type)
- struct_bytes
- elem_name:type_ref(int),bit_offset,field_bits;
- elem_name:type_ref(float),bit_offset,field_bits;
- elem_name:type_def(17)=type_desc(array)
- index_type(range of int from 0 to 7);
- element_type(char),bit_offset,field_bits;;",
- N_LSYM,NIL,NIL,NIL
-@end display
-
+@c FIXME: phony line break. Can probably be fixed by using an example
+@c with fewer fields.
@example
+# @r{128 is N_LSYM}
.stabs "s_tag:T16=s20s_int:1,0,32;s_float:12,32,32;
s_char_vec:17=ar1;0;7;2,64,64;s_next:18=*16,128,32;;",128,0,0,0
@end example
contains a type definition for an element which is a pointer to type 16.
@node Typedefs
-@section Giving a type a name
+@section Giving a Type a Name
To give a type a name, use the @samp{t} symbol descriptor. The type
-is specified by the type information (@pxref{String field}) for the stab.
+is specified by the type information (@pxref{String Field}) for the stab.
For example,
@example
-.stabs "s_typedef:t16",128,0,0,0
+.stabs "s_typedef:t16",128,0,0,0 # @r{128 is N_LSYM}
@end example
specifies that @code{s_typedef} refers to type number 16. Such stabs
-have symbol type @code{N_LSYM} (or @code{C_DECL} on AIX).
+have symbol type @code{N_LSYM} (or @code{C_DECL} for XCOFF).
If you are specifying the tag name for a structure, union, or
enumeration, use the @samp{T} symbol descriptor instead. I believe C is
AIX provides a type descriptor to specify it. The type descriptor is
@samp{o} and is followed by a name. I don't know what the name
means---is it always the same as the name of the type, or is this type
-descriptor used with a nameless stab (@pxref{String field})? There
+descriptor used with a nameless stab (@pxref{String Field})? There
optionally follows a comma followed by type information which defines
the type of this type. If omitted, a semicolon is used in place of the
comma and the type information, and the type is much like a generic
for @code{u_type} do not convey any infomation about its procedure local
scope.
-@display
-.stabs "name:sym_desc(union tag)type_def(22)=type_desc(union)
- byte_size(4)
- elem_name:type_ref(int),bit_offset(0),bit_size(32);
- elem_name:type_ref(float),bit_offset(0),bit_size(32);
- elem_name:type_ref(ptr to char),bit_offset(0),bit_size(32);;"
- N_LSYM, NIL, NIL, NIL
-@end display
-
+@c FIXME: phony line break. Can probably be fixed by using an example
+@c with fewer fields.
@smallexample
+# @r{128 is N_LSYM}
.stabs "u_tag:T23=u4u_int:1,0,32;u_float:12,0,32;u_char:21,0,32;;",
128,0,0,0
@end smallexample
The stab for the union variable is:
-@display
-.stabs "name:type_ref(u_tag)", N_LSYM, NIL, NIL, frame_ptr_offset
-@end display
-
@example
-.stabs "an_u:23",128,0,0,-20
+.stabs "an_u:23",128,0,0,-20 # @r{128 is N_LSYM}
@end example
-@node Function types
-@section Function types
+@samp{-20} specifies where the variable is stored (@pxref{Stack
+Variables}).
+
+@node Function Types
+@section Function Types
Various types can be defined for function variables. These types are
not used in defining functions (@pxref{Procedures}); they are used for
@samp{R} type descriptors.
First comes the type descriptor. If it is @samp{f} or @samp{F}, this
-type involves a function, and the type information for the return type
-of the function follows, followed by a comma. Then comes the number of
-parameters to the function and a semicolon. Then, for each parameter,
-there is the name of the parameter followed by a colon (this is only
-present for type descriptors @samp{R} and @samp{F} which represent
-Pascal function or procedure parameters), type information for the
-parameter, a comma, 0 if passed by reference or 1 if passed by value,
-and a semicolon. The type definition ends with a semicolon.
+type involves a function rather than a procedure, and the type
+information for the return type of the function follows, followed by a
+comma. Then comes the number of parameters to the function and a
+semicolon. Then, for each parameter, there is the name of the parameter
+followed by a colon (this is only present for type descriptors @samp{R}
+and @samp{F} which represent Pascal function or procedure parameters),
+type information for the parameter, a comma, 0 if passed by reference or
+1 if passed by value, and a semicolon. The type definition ends with a
+semicolon.
For example, this variable definition:
The variable defines a new type, 24, which is a pointer to another new
type, 25, which is a function returning @code{int}.
-@node Symbol tables
-@chapter Symbol information in symbol tables
+@node Symbol Tables
+@chapter Symbol Information in Symbol Tables
This chapter describes the format of symbol table entries
and how stab assembler directives map to them. It also describes the
transformations that the assembler and linker make on data from stabs.
@menu
-* Symbol table format::
-* Transformations on symbol tables::
+* Symbol Table Format::
+* Transformations On Symbol Tables::
@end menu
-@node Symbol table format
-@section Symbol table format
+@node Symbol Table Format
+@section Symbol Table Format
Each time the assembler encounters a stab directive, it puts
each field of the stab into a corresponding field in a symbol table
-entry of its output file. If the stab contains a @var{string} field, the
+entry of its output file. If the stab contains a string field, the
symbol table entry for that stab points to a string table entry
containing the string data from the stab. Assembler labels become
relocatable addresses. Symbol table entries in a.out have the format:
@};
@end example
-For @code{.stabs} directives, the @code{n_strx} field holds the offset
-in bytes from the start of the string table to the string table entry
-containing the @var{string} field. For other classes of stabs
-(@code{.stabn} and @code{.stabd}) this field is zero.
+If the stab has a string, the @code{n_strx} field holds the offset in
+bytes of the string within the string table. The string is terminated
+by a NUL character. If the stab lacks a string (for example, it was
+produced by a @code{.stabn} or @code{.stabd} directive), the
+@code{n_strx} field is zero.
Symbol table entries with @code{n_type} field values greater than 0x1f
originated as stabs generated by the compiler (with one random
exception). The other entries were placed in the symbol table of the
executable by the assembler or the linker.
-@node Transformations on symbol tables
-@section Transformations on symbol tables
+@node Transformations On Symbol Tables
+@section Transformations on Symbol Tables
The linker concatenates object files and does fixups of externally
defined symbols.
assembler and linker symbols, the columns are: @var{value}, @var{type},
@var{string}.
-Where the @var{value} field of a stab contains a frame pointer offset,
-or a register number, that @var{value} is unchanged by the rest of the
-build.
+The low 5 bits of the stab type tell the linker how to relocate the
+value of the stab. Thus for stab types like @code{N_RSYM} and
+@code{N_LSYM}, where the value is an offset or a register number, the
+low 5 bits are @code{N_ABS}, which tells the linker not to relocate the
+value.
-Where the @var{value} field of a stab contains an assembly language label,
+Where the value of a stab contains an assembly language label,
it is transformed by each build step. The assembler turns it into a
relocatable address and the linker turns it into an absolute address.
@menu
-* Transformations on static variables::
-* Transformations on global variables::
+* Transformations On Static Variables::
+* Transformations On Global Variables::
@end menu
-@node Transformations on static variables
-@subsection Transformations on static variables
+@node Transformations On Static Variables
+@subsection Transformations on Static Variables
This source line defines a static variable at file scope:
0000e00c - 00 0000 STSYM s_g_repeat:S1
@end example
-@node Transformations on global variables
-@subsection Transformations on global variables
+@node Transformations On Global Variables
+@subsection Transformations on Global Variables
Stabs for global variables do not contain location information. In
this case, the debugger finds location information in the assembler or
file (see below). The first one originated as a stab. The second one
is an external symbol. The upper case @samp{D} signifies that the
@code{n_type} field of the symbol table contains 7, @code{N_DATA} with
-local linkage. The @var{value} field is empty for the stab entry. For
-the linker symbol, it contains the relocatable address corresponding to
-the variable.
+local linkage. The stab's value is zero since the value is not used for
+@code{N_GSYM} stabs. The value of the linker symbol is the relocatable
+address corresponding to the variable.
@example
00000000 - 00 0000 GSYM g_foo:G2
@end example
@node Cplusplus
-@chapter GNU C++ stabs
+@chapter GNU C++ Stabs
@menu
-* Basic cplusplus types::
-* Simple classes::
-* Class instance::
+* Basic Cplusplus Types::
+* Simple Classes::
+* Class Instance::
* Methods:: Method definition
* Protections::
-* Method modifiers::
-* Virtual methods::
+* Method Modifiers::
+* Virtual Methods::
* Inheritence::
-* Virtual base classes::
-* Static members::
+* Virtual Base Classes::
+* Static Members::
@end menu
Type descriptors added for C++ descriptions:
gibberish. Can anyone say what really goes here?).
Note that there is a conflict between this and type attributes
-(@pxref{String field}); both use type descriptor @samp{@@}.
+(@pxref{String Field}); both use type descriptor @samp{@@}.
Fortunately, the @samp{@@} type descriptor used in this C++ sense always
will be followed by a digit, @samp{(}, or @samp{-}, and type attributes
never start with those things.
@end table
-@node Basic cplusplus types
-@section Basic types for C++
+@node Basic Cplusplus Types
+@section Basic Types For C++
<< the examples that follow are based on a01.C >>
.stabs "$vtbl_ptr_type:T17",128,0,0,0
@end example
-@node Simple classes
-@section Simple class definition
+@node Simple Classes
+@section Simple Class Definition
The stabs describing C++ language features are an extension of the
stabs describing C. Stabs representing C++ class types elaborate
.stabs "baseA:T20",128,0,0,0
@end smallexample
-@node Class instance
-@section Class instance
+@node Class Instance
+@section Class Instance
As shown above, describing even a simple C++ class definition is
accomplished by massively extending the stab format used in C to
@end example
@node Methods
-@section Method defintion
+@section Method Defintion
The class definition shown above declares Ameth. The C++ source below
defines Ameth:
pubMeth::24=##12;:f;2A.;;",128,0,0,0
@end smallexample
-@node Method modifiers
-@section Method modifiers (@code{const}, @code{volatile}, @code{const volatile})
+@node Method Modifiers
+@section Method Modifiers (@code{const}, @code{volatile}, @code{const volatile})
<< based on a6.C >>
ConstVolMeth::23=##12;:f;2D.;;",128,0,0,0
@end example
-@node Virtual methods
-@section Virtual methods
+@node Virtual Methods
+@section Virtual Methods
<< The following examples are based on a4.C >>
28;;D_virt::32:i;2A*-2147483646;31;;;~%20;",128,0,0,0
@end smallexample
-@node Virtual base classes
-@section Virtual base classes
+@node Virtual Base Classes
+@section Virtual Base Classes
A derived class object consists of a concatination in memory of the data
areas defined by each base class, starting with the leftmost and ending
virtual base pointer for @code{B} at 128, and @code{Ddat} at 160.
-@node Static members
-@section Static members
+@node Static Members
+@section Static Members
The data area for a class is a concatenation of the space used by the
data members of the class. If the class has virtual methods, a vtable
<< How is this reflected in stabs? See Cygnus bug #677 for some info. >>
-@node Stab types
-@appendix Table of stab types
+@node Stab Types
+@appendix Table of Stab Types
-The following are all the possible values for the stab @var{type} field, for
-@code{a.out} files, in numeric order. This does not apply to XCOFF.
+The following are all the possible values for the stab type field, for
+@code{a.out} files, in numeric order. This does not apply to XCOFF, but
+it does apply to stabs in ELF. Stabs in ECOFF use these values but add
+0x8f300 to distinguish them from non-stab symbols.
The symbolic names are defined in the file @file{include/aout/stabs.def}.
@menu
-* Non-stab symbol types:: Types from 0 to 0x1f
-* Stab symbol types:: Types from 0x20 to 0xff
+* Non-Stab Symbol Types:: Types from 0 to 0x1f
+* Stab Symbol Types:: Types from 0x20 to 0xff
@end menu
-@node Non-stab symbol types
-@appendixsec Non-stab symbol types
+@node Non-Stab Symbol Types
+@appendixsec Non-Stab Symbol Types
The following types are used by the linker and assembler, not by stab
directives. Since this document does not attempt to describe aspects of
File name of a @file{.o} file
@end table
-@node Stab symbol types
-@appendixsec Stab symbol types
+@node Stab Symbol Types
+@appendixsec Stab Symbol Types
The following symbol types indicate that this is a stab. This is the
full list of stab numbers, including stab types that are used in
@table @code
@item 0x20 N_GSYM
-Global symbol; see @ref{Global variables}.
+Global symbol; see @ref{Global Variables}.
@item 0x22 N_FNAME
-Function name (for BSD Fortran); see @ref{N_FNAME}.
+Function name (for BSD Fortran); see @ref{Procedures}.
@item 0x24 N_FUN
Function name (@pxref{Procedures}) or text segment variable
BSS segment file-scope variable; see @ref{Statics}.
@item 0x2a N_MAIN
-Name of main routine; see @ref{Main program}.
+Name of main routine; see @ref{Main Program}.
-@c FIXME: discuss this in the Statics node where we talk about
-@c the fact that the n_type indicates the section.
@item 0x2c N_ROSYM
Variable in @code{.rodata} section; see @ref{Statics}.
Debugger options (Solaris2).
@item 0x40 N_RSYM
-Register variable; see @ref{Register variables}.
+Register variable; see @ref{Register Variables}.
@item 0x42 N_M2C
Modula-2 compilation unit; see @ref{N_M2C}.
@item 0x44 N_SLINE
-Line number in text segment; see @ref{Line numbers}.
+Line number in text segment; see @ref{Line Numbers}.
@item 0x46 N_DSLINE
-Line number in data segment; see @ref{Line numbers}.
+Line number in data segment; see @ref{Line Numbers}.
@item 0x48 N_BSLINE
-Line number in bss segment; see @ref{Line numbers}.
+Line number in bss segment; see @ref{Line Numbers}.
@item 0x48 N_BROWS
Sun source code browser, path to @file{.cb} file; see @ref{N_BROWS}.
Last stab for module (Solaris2).
@item 0x64 N_SO
-Path and name of source file; see @ref{Source files}.
+Path and name of source file; see @ref{Source Files}.
@item 0x80 N_LSYM
-Stack variable (@pxref{Stack variables}) or type (@pxref{Typedefs}).
+Stack variable (@pxref{Stack Variables}) or type (@pxref{Typedefs}).
@item 0x82 N_BINCL
-Beginning of an include file (Sun only); see @ref{Include files}.
+Beginning of an include file (Sun only); see @ref{Include Files}.
@item 0x84 N_SOL
-Name of include file; see @ref{Include files}.
+Name of include file; see @ref{Include Files}.
@item 0xa0 N_PSYM
Parameter variable; see @ref{Parameters}.
@item 0xa2 N_EINCL
-End of an include file; see @ref{Include files}.
+End of an include file; see @ref{Include Files}.
@item 0xa4 N_ENTRY
Alternate entry point; see @ref{N_ENTRY}.
@item 0xc0 N_LBRAC
-Beginning of a lexical block; see @ref{Block structure}.
+Beginning of a lexical block; see @ref{Block Structure}.
@item 0xc2 N_EXCL
-Place holder for a deleted include file; see @ref{Include files}.
+Place holder for a deleted include file; see @ref{Include Files}.
@item 0xc4 N_SCOPE
Modula2 scope information (Sun linker); see @ref{N_SCOPE}.
@item 0xe0 N_RBRAC
-End of a lexical block; see @ref{Block structure}.
+End of a lexical block; see @ref{Block Structure}.
@item 0xe2 N_BCOMM
-Begin named common block; see @ref{Common blocks}.
+Begin named common block; see @ref{Common Blocks}.
@item 0xe4 N_ECOMM
-End named common block; see @ref{Common blocks}.
+End named common block; see @ref{Common Blocks}.
@item 0xe8 N_ECOML
-Member of a common block; see @ref{Common blocks}.
+Member of a common block; see @ref{Common Blocks}.
@c FIXME: How does this really work? Move it to main body of document.
@item 0xea N_WITH
@tableindent=.8in
@end iftex
-@node Symbol descriptors
-@appendix Table of symbol descriptors
+@node Symbol Descriptors
+@appendix Table of Symbol Descriptors
-These tell in the @code{.stabs} @var{string} field what kind of symbol
-the stab represents. They follow the colon which follows the symbol
-name. @xref{String field}, for more information about their use.
+The symbol descriptor is the character which follows the colon in many
+stabs, and which tells what kind of stab it is. @xref{String Field},
+for more information about their use.
@c Please keep this alphabetical
@table @code
@item @var{digit}
@itemx (
@itemx -
-Variable on the stack; see @ref{Stack variables}.
+Variable on the stack; see @ref{Stack Variables}.
@item a
-Parameter passed by reference in register; see @ref{Reference parameters}.
+Parameter passed by reference in register; see @ref{Reference Parameters}.
+
+@item b
+Based variable; see @ref{Parameters}.
@item c
Constant; see @ref{Constants}.
@item C
-Conformant array bound (Pascal, maybe other languages); @ref{Reference
-parameters}. Name of a caught exception (GNU C++). These can be
+Conformant array bound (Pascal, maybe other languages); @ref{Conformant
+Arrays}. Name of a caught exception (GNU C++). These can be
distinguished because the latter uses @code{N_CATCH} and the former uses
another symbol type.
@item d
-Floating point register variable; see @ref{Register variables}.
+Floating point register variable; see @ref{Register Variables}.
@item D
-Parameter in floating point register; see @ref{Register parameters}.
+Parameter in floating point register; see @ref{Register Parameters}.
@item f
File scope function; see @ref{Procedures}.
Global function; see @ref{Procedures}.
@item G
-Global variable; see @ref{Global variables}.
+Global variable; see @ref{Global Variables}.
@item i
-@xref{Register parameters}.
+@xref{Register Parameters}.
@item I
-Internal (nested) procedure; see @ref{Nested procedures}.
+Internal (nested) procedure; see @ref{Nested Procedures}.
@item J
-Internal (nested) function; see @ref{Nested procedures}.
+Internal (nested) function; see @ref{Nested Procedures}.
@item L
Label name (documented by AIX, no further information known).
Static Procedure; see @ref{Procedures}.
@item R
-Register parameter; see @ref{Register parameters}.
+Register parameter; see @ref{Register Parameters}.
@item r
-Register variable; see @ref{Register variables}.
+Register variable; see @ref{Register Variables}.
@item S
File scope variable; see @ref{Statics}.
Enumeration, structure, or union tag; see @ref{Typedefs}.
@item v
-Parameter passed by reference; see @ref{Reference parameters}.
+Parameter passed by reference; see @ref{Reference Parameters}.
@item V
Procedure scope static variable; see @ref{Statics}.
@item x
-Conformant array; see @ref{Conformant arrays}.
+Conformant array; see @ref{Conformant Arrays}.
@item X
Function return variable; see @ref{Parameters}.
@end table
-@node Type descriptors
-@appendix Table of type descriptors
+@node Type Descriptors
+@appendix Table of Type Descriptors
-These tell in the @code{.stabs} @var{string} field what kind of type is being
-defined. They follow the type number and an equals sign.
-@xref{String field}, for more information about their use.
+The type descriptor is the character which follows the type number and
+an equals sign. It specifies what kind of type is being defined.
+@xref{String Field}, for more information about their use.
@table @code
@item @var{digit}
@itemx (
-Type reference; see @ref{String field}.
+Type reference; see @ref{String Field}.
@item -
-Reference to builtin type; see @ref{Negative type numbers}.
+Reference to builtin type; see @ref{Negative Type Numbers}.
@item #
Method (C++); see @ref{Cplusplus}.
@item *
-Pointer; see @ref{Miscellaneous types}.
+Pointer; see @ref{Miscellaneous Types}.
@item &
Reference (C++).
@item @@
-Type Attributes (AIX); see @ref{String field}. Member (class and variable)
+Type Attributes (AIX); see @ref{String Field}. Member (class and variable)
type (GNU C++); see @ref{Cplusplus}.
@item a
Open array; see @ref{Arrays}.
@item b
-Pascal space type (AIX); see @ref{Miscellaneous types}. Builtin integer
-type (Sun); see @ref{Builtin type descriptors}.
+Pascal space type (AIX); see @ref{Miscellaneous Types}. Builtin integer
+type (Sun); see @ref{Builtin Type Descriptors}.
@item B
-Volatile-qualified type; see @ref{Miscellaneous types}.
+Volatile-qualified type; see @ref{Miscellaneous Types}.
@item c
-Complex builtin type; see @ref{Builtin type descriptors}.
+Complex builtin type; see @ref{Builtin Type Descriptors}.
@item C
COBOL Picture type. See AIX documentation for details.
@item d
-File type; see @ref{Miscellaneous types}.
+File type; see @ref{Miscellaneous Types}.
@item D
N-dimensional dynamic array; see @ref{Arrays}.
N-dimensional subarray; see @ref{Arrays}.
@item f
-Function type; see @ref{Function types}.
+Function type; see @ref{Function Types}.
@item F
-Pascal function parameter; see @ref{Function types}
+Pascal function parameter; see @ref{Function Types}
@item g
-Builtin floating point type; see @ref{Builtin type descriptors}.
+Builtin floating point type; see @ref{Builtin Type Descriptors}.
@item G
COBOL Group. See AIX documentation for details.
@item i
-Imported type; see @ref{Cross-references}.
+Imported type; see @ref{Cross-References}.
@item k
-Const-qualified type; see @ref{Miscellaneous types}.
+Const-qualified type; see @ref{Miscellaneous Types}.
@item K
COBOL File Descriptor. See AIX documentation for details.
@item M
-Multiple instance type; see @ref{Miscellaneous types}.
+Multiple instance type; see @ref{Miscellaneous Types}.
@item n
String type; see @ref{Strings}.
Opaque type; see @ref{Typedefs}.
@item p
-Procedure; see @ref{Function types}.
+Procedure; see @ref{Function Types}.
@item P
Packed array; see @ref{Arrays}.
Range type; see @ref{Subranges}.
@item R
-Builtin floating type; see @ref{Builtin type descriptors} (Sun). Pascal
-subroutine parameter; see @ref{Function types} (AIX). Detecting this
+Builtin floating type; see @ref{Builtin Type Descriptors} (Sun). Pascal
+subroutine parameter; see @ref{Function Types} (AIX). Detecting this
conflict is possible with careful parsing (hint: a Pascal subroutine
parameter type will always contain a comma, and a builtin type
descriptor never will).
Structure type; see @ref{Structures}.
@item S
-Set type; see @ref{Miscellaneous types}.
+Set type; see @ref{Miscellaneous Types}.
@item u
Union; see @ref{Unions}.
union within a struct in C. See AIX documentation for details.
@item w
-Wide character; see @ref{Builtin type descriptors}.
+Wide character; see @ref{Builtin Type Descriptors}.
@item x
-Cross-reference; see @ref{Cross-references}.
+Cross-reference; see @ref{Cross-References}.
@item z
gstring; see @ref{Strings}.
@end table
-@node Expanded reference
-@appendix Expanded reference by stab type
+@node Expanded Reference
+@appendix Expanded Reference by Stab Type
@c FIXME: This appendix should go away; see N_PSYM or N_SO for an example.
For a full list of stab types, and cross-references to where they are
-described, see @ref{Stab types}. This appendix just duplicates certain
+described, see @ref{Stab Types}. This appendix just duplicates certain
information from the main body of this document; eventually the
information will all be in one place.
Finally, any further information.
@menu
-* N_FNAME:: Function name (BSD Fortran)
* N_PC:: Pascal global symbol
* N_NSYMS:: Number of symbols
* N_NOMAP:: No DST map
* N_LENG:: Length of preceding entry
@end menu
-@node N_FNAME
-@section N_FNAME
-
-@deffn @code{.stabs} N_FNAME
-@findex N_FNAME
-Function name (for BSD Fortran).
-
-@example
-"name" -> "function_name"
-@end example
-
-Only the @var{string} field is significant. The location of the symbol is
-obtained from the corresponding extern symbol.
-@end deffn
-
@node N_PC
@section N_PC
<<?>>
"path to associated @file{.cb} file"
-Note: @var{type} field value overlaps with N_BSLINE.
+Note: N_BROWS has the same value as N_BSLINE.
@end deffn
@node N_DEFD
@findex N_DEFD
GNU Modula2 definition module dependency.
-GNU Modula-2 definition module dependency. @var{value} is the modification
-time of the definition file. @var{other} is non-zero if it is imported with
-the GNU M2 keyword @code{%INITIALIZE}. Perhaps @code{N_M2C} can be used
-if there are enough empty fields?
+GNU Modula-2 definition module dependency. The value is the
+modification time of the definition file. The other field is non-zero
+if it is imported with the GNU M2 keyword @code{%INITIALIZE}. Perhaps
+@code{N_M2C} can be used if there are enough empty fields?
@end deffn
@node N_EHDECL
@findex N_CATCH
GNU C++ @code{catch} clause
-GNU C++ @code{catch} clause. @code{value} is its address. @code{desc}
+GNU C++ @code{catch} clause. The value is its address. The desc field
is nonzero if this entry is immediately followed by a @code{CAUGHT} stab
saying what exception was caught. Multiple @code{CAUGHT} stabs means
-that multiple exceptions can be caught here. If @code{desc} is 0, it
-means all exceptions are caught here.
+that multiple exceptions can be caught here. If desc is 0, it means all
+exceptions are caught here.
@end deffn
@node N_SSYM
@findex N_SSYM
Structure or union element.
-@code{value} is offset in the structure.
+The value is the offset in the structure.
<<?looking at structs and unions in C I didn't see these>>
@end deffn
@deffn @code{.stabn} N_ENTRY
@findex N_ENTRY
Alternate entry point.
-@code{value} is its address.
+The value is its address.
<<?>>
@end deffn
@deffn @code{.stabn} N_LENG
@findex N_LENG
Second symbol entry containing a length-value for the preceding entry.
-The @var{value} is the length.
+The value is the length.
@end deffn
@node Questions
-@appendix Questions and anomalies
+@appendix Questions and Anomalies
@itemize @bullet
@item
@c I think this is changed in GCC 2.4.5 to put the line number there.
For GNU C stabs defining local and global variables (@code{N_LSYM} and
-@code{N_GSYM}), the @var{desc} field is supposed to contain the source
-line number on which the variable is defined. In reality the @var{desc}
+@code{N_GSYM}), the desc field is supposed to contain the source
+line number on which the variable is defined. In reality the desc
field is always 0. (This behavior is defined in @file{dbxout.c} and
-putting a line number in @var{desc} is controlled by @samp{#ifdef
+putting a line number in desc is controlled by @samp{#ifdef
WINNING_GDB}, which defaults to false). GDB supposedly uses this
information if you say @samp{list @var{var}}. In reality, @var{var} can
be a variable defined in the program and GDB says @samp{function
@c dbx?
@end itemize
-@node XCOFF differences
-@appendix Differences between GNU stabs in a.out and GNU stabs in XCOFF
+@node XCOFF Differences
+@appendix Differences Between GNU Stabs in a.out and GNU Stabs in XCOFF
@c FIXME: Merge *all* these into the main body of the document.
The AIX/RS6000 native object file format is XCOFF with stabs. This
@c used (I suspect not), explain clearly, and move to node Statics.
Exception: initialised static @code{N_STSYM} and un-initialized static
@code{N_LCSYM} both map to the @code{C_STSYM} storage class. But the
-destinction is preserved because in XCOFF @code{N_STSYM} and
+distinction is preserved because in XCOFF @code{N_STSYM} and
@code{N_LCSYM} must be emited in a named static block. Begin the block
with @samp{.bs s[RW] data_section_name} for @code{N_STSYM} or @samp{.bs
s bss_section_name} for @code{N_LCSYM}. End the block with @samp{.es}.
stab type storage class
-------------------------------
N_GSYM C_GSYM
-N_FNAME unknown
+N_FNAME unused
N_FUN C_FUN
N_STSYM C_STSYM
N_LCSYM C_STSYM
-N_MAIN unkown
+N_MAIN unknown
N_PC unknown
N_RSYM C_RSYM
unknown C_RPSYM
N_LENG unknown
@end example
-@node Sun differences
-@appendix Differences between GNU stabs and Sun native stabs
+@node Sun Differences
+@appendix Differences Between GNU Stabs and Sun Native Stabs
@c FIXME: Merge all this stuff into the main body of the document.
@code{N_LSYM}. Sun doc talks about using @code{N_GSYM} too.
@item
-Sun C stabs use type number pairs in the format (@var{a},@var{b}) where
-@var{a} is a number starting with 1 and incremented for each sub-source
-file in the compilation. @var{b} is a number starting with 1 and
+Sun C stabs use type number pairs in the format
+(@var{file-number},@var{type-number}) where @var{file-number} is a
+number starting with 1 and incremented for each sub-source file in the
+compilation. @var{type-number} is a number starting with 1 and
incremented for each new type defined in the compilation. GNU C stabs
use the type number alone, with no source file number.
@end itemize
-@node Stabs in ELF
-@appendix Using stabs with the ELF object file format
+@node Stabs In ELF
+@appendix Using Stabs With The ELF Object File Format
The ELF object file format allows tools to create object files with
custom sections containing any arbitrary data. To use stabs in ELF
of the ELF file itself, as determined from the @code{EI_DATA} field in
the @code{e_ident} member of the ELF header.
-@c Is "source file" the right term for this concept? We don't mean that
-@c there is a separate one for include files (but "object file" or
-@c "object module" isn't quite right either; the output from ld -r is a
-@c single object file but contains many source files).
-The first stab in the @code{.stab} section for each source file is
+The first stab in the @code{.stab} section for each compilation unit is
synthetic, generated entirely by the assembler, with no corresponding
@code{.stab} directive as input to the assembler. This stab contains
the following fields:
header @code{sh_type} member set to @code{SHT_STRTAB} to mark it as a
string table.
-Because the linker does not process the @code{.stab} section in any
-special way, none of the addresses in the @code{n_value} field of the
-stabs are relocated by the linker. Instead they are relative to the
-source file (or some entity smaller than a source file, like a
-function). To find the address of each section corresponding to a given
-source file, the (compiler? assembler?) puts out symbols giving the
-address of each section for a given source file. Since these are normal
-ELF symbols, the linker can relocate them correctly. They are
-named @code{Bbss.bss} for the bss section, @code{Ddata.data} for
-the data section, and @code{Drodata.rodata} for the rodata section. I
-haven't yet figured out how the debugger gets the address for the text
-section.
+To keep linking fast, it is a bad idea to have the linker relocating
+stabs, so (except for Solaris 2.2 and earlier, see below) none of the
+addresses in the @code{n_value} field of the stabs are relocated by the
+linker. Instead they are relative to the source file (or some entity
+smaller than a source file, like a function). To find the address of
+each section corresponding to a given source file, the compiler puts out
+symbols giving the address of each section for a given source file.
+Since these are ELF (not stab) symbols, the linker can relocate them
+correctly. They are named @code{Bbss.bss} for the bss section,
+@code{Ddata.data} for the data section, and @code{Drodata.rodata} for
+the rodata section. For the text section, there is no such symbol. GCC
+does not provide these symbols; it instead relies on the stabs getting
+relocated, which loses for Solaris 2.3 (see below). Thus address which
+would normally be relative to @code{Bbss.bss}, etc., are absolute. The
+linker provided with Solaris 2.2 and earlier relocates stabs using
+relocation information from a @code{.rela.stab} section, which means
+that the value of an @code{N_FUN} stab in an executable is the actual
+address. I think this is pretty much just standard ELF relocations, as
+it would do for any section, rather than a special-purpose stabs hack.
+For Solaris 2.3 and later, the linker ignores relocations for the stabs
+section. The value of a @code{N_FUN} stab is zero and the address of a
+function can be obtained from the ELF (non-stab) symbols. Sun, in
+reference to bug 1142109, has verified that this is intentional.
+Because looking things up in the ELF symbols is slow and GDB lacks code
+to do this this, it would probably be better to use a @code{Ttext.text}
+symbol for stabs-in-elf on non-Solaris machines, and make the address in
+the @code{N_FUN} relative to the @code{Ttext.text} symbol. In addition
+to @code{N_FUN} symbols, whether the linker relocates stabs also affects
+some @code{N_ROSYM}, @code{N_STSYM}, and @code{N_LCSYM} symbols; see
+@ref{Statics}.
@node Symbol Types Index
@unnumbered Symbol Types Index
projects / binutils.git / blobdiff