General updates for 5.1/5.2 lists.

[binutils.git] / gdb / TODO

If you find inaccuracies in this list, please send mail to
[email protected].  If you would like to work on any
of these, you should consider sending mail to the same address, to
find out whether anyone else is working on it.


                        GDB 5.1 - Fixes
                        ===============

Below is a list of problems identified during the GDB 5.0 release
cycle.  People hope to have these problems fixed in 5.1.

-- 2001-03-08

Update GDB's coding standard documentation.  Known topics:

       o     alloca/malloc et.al.

       o     typedef and structs

       o        ISO-C

and most likely also:

       o         include conventions

--

Obsolete ser-ocd.c.

--

Wow, three bug reports for the same problem in one day!  We should
probably make fixing this a real priority :-).

Anyway, thanks for reporting.

The following patch will fix the problems with setting breakpoints in
dynamically loaded objects:

   http://sourceware.cygnus.com/ml/gdb-patches/2000-05/msg00230.html

This patch isn't checked in yet (ping Michael/JimB), but I hope this
will be in the next GDB release.

There should really be a test in the testsuite for this problem, since
it keeps coming up :-(.  Any volunteers?

Mark

--

x86 linux GDB and SIGALRM (???)
http://sourceware.cygnus.com/ml/gdb/2000-q1/msg00803.html

This problem has been fixed, but a regression test still needs to be
added to the testsuite:
http://sourceware.cygnus.com/ml/gdb-patches/2000-05/msg00309.html

Mark

[The test has been submitted for approval - cagney]

--

RFD: infrun.c: No bpstat_stop_status call after proceed over break?
http://sourceware.cygnus.com/ml/gdb-patches/2000-q1/msg00665.html

GDB misses watchpoint triggers after proceeding over a breakpoint on
x86 targets.

--

GDB 5.0 doesn't work on Linux/SPARC

There are two parts to this.

      o   GDB 5.0 doesn't work on GNU/Linux/SPARC32

      o   GDB 5.0 doesn't work on the new target
          GNU/Linux/SPARC64

GDB does build on both these targets.

The first problem is the one that should be fixed.

--

                GDB 5.1 - New features
                ======================

The following new features should be included in 5.1.

--

Enable MI by default.  Old code can be deleted after 5.1 is out.

Issues:

        o       syntax change where a list would
                look like:
                     [ foo=a, foo=b, foo=c ]
                instead of
                     { foo=a, foo=b, foo=c }

        o       kill off the idea of a reverse
                query.

        o       review test cases

        o       enable it

--

Pascal (Pierre Muller, David Taylor)

Pierre Muller has contributed patches for adding Pascal Language
support to GDB.

2 pascal language patches inserted in database
http://sourceware.cygnus.com/ml/gdb/2000-q1/msg00521.html

Indent -gnu ?
http://sourceware.cygnus.com/ml/gdb/2000-q1/msg00496.html

[I think this has been merged, need to confirm - cagney]

--

Java (Anthony Green, David Taylor)

Anthony Green has a number of Java patches that did not make it into
the 5.0 release.  The first two are in cvs now, but the third needs
some fixing up before it can go in.

Patch: java tests
http://sourceware.cygnus.com/ml/gdb-patches/2000-q1/msg00512.html

Patch: java booleans
http://sourceware.cygnus.com/ml/gdb-patches/2000-q1/msg00515.html

Patch: handle N_MAIN stab
http://sourceware.cygnus.com/ml/gdb-patches/2000-q1/msg00527.html

-- 2001-03-08

Add CRIS target.

A predicate to this is the multi-arching of SOFTWARE_SINGLE_STEP().  A
patch has been submitted.

--

                GDB 5.1 - Cleanups
                ==================

The following code cleanups will hopefully be applied to GDB 5.1.

-- 2001-03-26

Resolve the build status of all broken targets as identified by the
MAINTAINERS file.

        o       arm-* vs NetBSD's lack of ``unix''
        o       arm-* vs IRIX (see below)

--

Fix copyright notices.

Turns out that ``1998-2000'' isn't considered valid :-(

http://sourceware.cygnus.com/ml/gdb-patches/2000-05/msg00467.html

--

                GDB 5.1 - Known Problems
                ========================

--

z8k

The z8k has suffered bit rot and is known to not build.  The problem
was occuring in the opcodes directory.

--

m88k

The m88k has suffered bit rot and is known to not build.

--

Solaris 8 x86 CURSES_H problem
http://sources.redhat.com/ml/gdb/2000-07/msg00038.html

The original problem was worked around with:

    2000-06-06  Michael Snyder  <[email protected]>

        * configure.in: Enable autoconf to find curses.h on Solaris 2.8.
        * configure: Regenerate.

When building both GDB and SID using the same source tree the problem
will still occure. sid/component/configure.in mis-configures
<curses.h> and leaves wrong information in the config cache.

--

                GDB 5.2 - Fixes
                ===============

--

Thread support.  Right now, as soon as a thread finishes and exits,
you're hosed.  This problem is reported once a week or so.

--

                GDB 5.2 - New features
                ======================

--

GCC 3.0 ABI support (but hopefully sooner...).

--

Objective C/C++ support (but hopefully sooner...).

--

                GDB 5.2 - Cleanups
                ==================

The following cleanups have been identified as part of GDB 5.2.

--

Remove old code that does not use ui_out functions and all the related
"ifdef"s.  This also allows the elimination of -DUI_OUT from
Makefile.in and configure.in.

--

Compiler warnings.

Eliminate warnings for all targets on at least one host for one of the
-W flags.  Flags up for debate include: -Wswitch -Wcomment -trigraphs
-Wtrigraphs -Wunused-function -Wunused-label -Wunused-variable
-Wunused-value -Wchar-subscripts -Wtraditional -Wshadow -Wcast-qual
-Wcast-align -Wwrite-strings -Wconversion -Wstrict-prototypes
-Wmissing-prototypes -Wmissing-declarations -Wredundant-decls
-Woverloaded-virtual -Winline

--

Deprecate, if not delete, the following:

        register[]
        register_valid[]
        register_buffer()
        REGISTER_BYTE()
                Replaced by, on the target side
                  supply_register()
                and on core-gdb side:
                  {read,write}_register_gen()
                Remote.c will need to use something
                other than REGISTER_BYTE() and
                REGISTER_RAW_SIZE() when unpacking
                [gG] packets.

        STORE_PSEUDO_REGISTER
        FETCH_PSEUDO_REGISTER
                Now handed by the methods
                  gdbarch_{read,write}_register()
                which sits between core GDB and
                the register cache.

        REGISTER_CONVERTIBLE
        REGISTER_CONVERT_TO_RAW
        REGISTER_CONVERT_TO_VIRTUAL
                I think these three are redundant.
                gdbarch_register_{read,write} can
                do any conversion it likes.

        REGISTER_VIRTUAL_SIZE
        MAX_REGISTER_VIRTUAL_SIZE
        REGISTER_VIRTUAL_TYPE
                I think these can be replaced by
                the pair:
                  FRAME_REGISTER_TYPE(frame, regnum)
                  REGISTER_TYPE(regnum)

        DO_REGISTERS_INFO
                Replace with
                 FRAME_REGISTER_INFO (frame, ...)

        REGISTER_SIM_REGNO()
                If nothing else rename this so that
                how it relates to rawreg and the
                regnum is clear.

        REGISTER_BYTES
                The size of the cache can be computed
                on the fly.

        IS_TRAPPED_INTERNALVAR
                The pseudo registers should eventually make
                this redundant.

--

Obsolete the targets.

arm*-wince-pe
mips*-*-pe
sh*-*-pe

Obsolete the protocols:

RDB

``As of version 5.3, WindRiver has removed the RDB server (RDB
protocol support is built into gdb).''  -- Till.

--

Restructure gdb directory tree so that it avoids any 8.3 and 14
filename problems.

--

Convert GDB build process to AUTOMAKE.

See also sub-directory configure below.

The current convention is (kind of) to use $(<header>_h) in all
dependency lists.  It isn't done in a consistent way.

--

                GDB 5.2 - Known Problems
                ========================

--

                Code Cleanups: General
                ======================

The following are more general cleanups and fixes.  They are not tied
to any specific release.

--

Investigate changing --target=a29k-amd-udi to a29k-*-coff* and
rationalize *.mt files.  The got-ya is in remote-eb.c - it has its own
custom tty manipulation - it should be using the serial object.

--

Rename read_register{,_pid}() to read_unsigned_register{,_pid}().

--

Can't build IRIX -> arm GDB.
http://sourceware.cygnus.com/ml/gdb-patches/2000-04/msg00356.html

David Whedon writes:
> Now I'm building for an embedded arm target.  If there is a way of turning
> remote-rdi off, I couldn't find it. It looks like it gets built by default
> in gdb/configure.tgt(line 58) Anyway, the build dies in
> gdb/rdi-share/unixcomm.c.  SERPORT1 et. al. never get defined because we
> aren't one of the architectures supported.

--

Problem with weak functions
http://sourceware.cygnus.com/ml/gdb/2000-05/msg00060.html

Dan Nicolaescu writes:
> It seems that gdb-4.95.1  does not display correctly the function when
> stoping in weak functions. 
> 
> It stops in a function that is defined as weak, not in the function
> that is actually run... 

--

Follow through `make check' with --enable-shared.

When the srcware tree is configured with --enable-shared, the `expect'
program won't run properly.  Jim Wilson found out gdb has a local hack
to set LD_LIBRARY_PATH, but, AFAIK, no other project has been hacked
similarly.

http://sourceware.cygnus.com/ml/gdb/2000-q1/msg00845.html

--

Delete macro TARGET_BYTE_ORDER_SELECTABLE.

Patches in the database.

--

printcmd.c (print_address_numeric):

NOTE: This assumes that the significant address information is kept in
the least significant bits of ADDR - the upper bits were either zero
or sign extended.  Should ADDRESS_TO_POINTER() or some
ADDRESS_TO_PRINTABLE() be used to do the conversion?

--

The BFD directory requires bug-fixed AUTOMAKE et.al.

AUTOMAKE 1.4 incorrectly set the TEXINPUTS environment variable.  It
contained the full path to texinfo.tex when it should have only
contained the directory.  The bug has been fixed in the current
AUTOMAKE sources.  Automake snapshots can be found in:
        ftp://sourceware.cygnus.com/pub/gdb/snapshots
and     ftp://sourceware.cygnus.com/pub/binutils

--

Find something better than DEFAULT_BFD_ARCH, DEFAULT_BFD_VEC to
determine the default isa/byte-order.

--

Rely on BFD_BIG_ENDIAN and BFD_LITTLE_ENDIAN instead of host dependent
BIG_ENDIAN and LITTLE_ENDIAN.

--

Eliminate more compiler warnings.

Of course there also needs to be the usual debate over which warnings
are valid and how to best go about this.

One method: choose a single option; get agreement that it is
reasonable; try it out to see if there isn't anything silly about it
(-Wunused-parameters is an example of that) then incrementally hack
away.

The other method is to enable all warnings and eliminate them from one
file at a time.

--

Elimination of ``(catch_errors_ftype *) func''.

Like make_cleanup_func it isn't portable.
http://sourceware.cygnus.com/ml/gdb-patches/2000-q1/msg00791.html
http://sourceware.cygnus.com/ml/gdb-patches/2000-q1/msg00814.html

--

Nuke #define CONST_PTR.

--

Nuke USG define.

--

[PATCH/5] src/intl/Makefile.in:distclean additions
http://sourceware.cygnus.com/ml/gdb-patches/2000-04/msg00363.html

Do not forget to merge the patch back into the trunk.

--

Rationalize the host-endian code (grep for HOST_BYTE_ORDER).

At present defs.h includes <endian.h> (which is linux specific) yet
almost nothing depends on it.  Suggest "gdb_endian.h" which can also
handle <machine/endian.h> and only include that where it is really
needed.

--

Replace savestring() with something from libiberty.

An xstrldup()? but that would have different semantics.

--

Rationalize use of floatformat_unknown in GDB sources.

Instead of defaulting to floatformat_unknown, should hosts/targets
specify the value explicitly?

http://sourceware.cygnus.com/ml/gdb-patches/2000-05/msg00447.html

--

Add a ``name'' member to include/floatformat.h:struct floatformat.
Print that name in gdbarch.c.

--

Sort out the harris mess in include/floatformat.h (it hardwires two
different floating point formats).

--

See of the GDB local floatformat_do_doublest() and libiberty's
floatformat_to_double (which was once GDB's ...) can be merged some
how.

--

Eliminate mmalloc(), mstrsave() et.al. from GDB.

Also eliminate it from defs.h.

--

Eliminate PTR.  ISO-C allows ``void *''.

--

Eliminate abort ().

GDB should never abort.  GDB should either throw ``error ()'' or
``internal_error ()''.  Better still GDB should naturally unwind with
an error status.

--

GDB probably doesn't build on FreeBSD pre 2.2.x
http://sourceware.cygnus.com/ml/gdb-patches/2000-05/msg00378.html

Fixes to get FreeBSD working on 2.2.x, 3.x and 4.x caused the code to
suffer bit rot.

--

Deprecate "fg".  Apparently ``fg'' is actually continue.

http://sourceware.cygnus.com/ml/gdb-patches/2000-05/msg00417.html

--

Deprecate current use of ``floatformat_unknown''.

Require all targets to explicitly provide their float format instead
of defaulting to floatformat unknown.  Doing the latter leads to nasty
bugs.

http://sourceware.cygnus.com/ml/gdb-patches/2000-05/msg00447.html

--

Rationalize floatformat_to_double() vs floatformat_to_doublest().

Looks like GDB migrated floatformat_to_double() to libiberty but then
turned around and created a ..._to_doublest() the latter containing
several bug fixes.

http://sourceware.cygnus.com/ml/gdb-patches/2000-05/msg00472.html

--

Move floatformat_ia64_ext to libiberty/include floatformat.[ch].

http://sourceware.cygnus.com/ml/gdb-patches/2000-05/msg00466.html

--

The ``maintenance deprecate set endian big'' command doesn't notice
that it is deprecating ``set endian'' and not ``set endian big'' (big
is implemented using an enum).  Is anyone going to notice this?

--

When tab expanding something like ``set arch<tab>'' ignore the
deprecated ``set archdebug'' and expand to ``set architecture''.

--

Eliminate ``arm_register_names[j] = (char *) regnames[j]'' and the
like from arm-tdep.c.

--

Fix uses of ->function.cfunc = set_function().

The command.c code calls sfunc() when a set command.  Rather than
change it suggest fixing the callback function so that it is more
useful.  See:

http://sourceware.cygnus.com/ml/gdb-patches/2000-06/msg00062.html

See also ``Fix implementation of  ``target xxx''.'' below.

--

IRIX 3.x support is probably broken.

--

Delete sim/SIM_HAVE_BREAKPOINTS and gdb/SIM_HAS_BREAKPOINTS.
http://sourceware.cygnus.com/ml/gdb-patches/2000-07/msg00042.html

Apart from the d30v, are there any sim/common simulators that make use
of this?

A brief summary of what happened is that sim/common/sim-break.c was
created as a good idea.  It turned out a better idea was to use
SIM_SIGBREAK and have GDB pass back sim_resume (..., SIGBREAK).

--

Move remote_remove_hw_breakpoint, remote_insert_hw_breakpoint,
remote_remove_watchpoint, remote_insert_watchpoint into target vector.

--

Eliminate ``extern'' from C files.

--

Replace ``STREQ()'' et.al. with ``strcmp() == 0'' et.al.

Extreme care is recommeded - perhaps only modify tests that are
exercised by the testsuite (as determined using some type of code
coverage analysis).

--

Replace the file gdb/CONTRIBUTE with a file that is generated from the
gdb/doc/*.texinfo directory.

--

Rewrite/break up sparcl-tdep.c so that it uses ser*.c as the mechanism
for accessing either the serial or UDP port.

--

                        New Features and Fixes
                        ======================

These are harder than cleanups but easier than work involving
fundamental architectural change.

--

Hardware watchpoint problems on x86 OSes, including Linux:

1. Delete/disable hardware watchpoints should free hardware debug
registers. 
2. Watch for different values on a viariable with one hardware debug
register.

According to Eli Zaretskii <[email protected]>:

These are not GDB/ia32 issues per se: the above features are all
implemented in the DJGPP port of GDB and work in v5.0.  Every
x86-based target should be able to lift the relevant parts of
go32-nat.c and use them almost verbatim.  You get debug register
sharing through reference counts, and the ability to watch large
regions (up to 16 bytes) using multiple registers.  (The required
infrastructure in high-level GDB application code, mostly in
breakpoint.c, is also working since v5.0.)

--

Add built-by, build-date, tm, xm, nm and anything else into gdb binary
so that you can see how the GDB was created.

--

Add an "info bfd" command that displays supported object formats,
similarly to objdump -i.

Is there a command already?

--

Fix ``I'm sorry, Dave, I can't do that.'' from symfile.c.

This requires internationalization.

--

Add support for:
 
(gdb) p fwprintf(stdout,L"%S\n", f)
No symbol "L" in current context.

--

Cleanup configury support for optional sub-directories.

Check how GCC handles multiple front ends for an example of how things
could work.  A tentative first step is to rationalize things so that
all sub directories are handled in a fashion similar to gdb/mi.

See also automake above.

--

Add a transcript mechanism to GDB.

Such a mechanism might log all gdb input and output to a file in a
form that would allow it to be replayed.  It could involve ``gdb
--transcript=FILE'' or it could involve ``(gdb) transcript file''.

--

Can the xdep files be replaced by autoconf?

--

Document trace machinery

--

Document ui-out and ui-file.

http://sourceware.cygnus.com/ml/gdb/2000-04/msg00121.html

--

Update texinfo.tex to latest?

--

Incorporate agentexpr.texi into gdb.texinfo

agentexpr.texi mostly describes the details of the byte code used for
tracepoints, not the internals of the support for this in GDB.  So it
looks like gdb.texinfo is a better place for this information.

http://sourceware.cygnus.com/ml/gdb-patches/2000-04/msg00566.html

--

Document overlay machinery.

--

``(gdb) catch signal SIGNAL''

Overlaps with ``handle SIGNAL'' but the implied behavior is different.
You can attach commands to a catch but not a handle.  A handle has a
limited number of hardwired actions.

--

Fix TUI

     o  readline/*.h bitrot

        The TUI isn't up-to-date with
        respect to the readline currently
        bundled with GDB.  Importing a
        new readline is on the 5.1 wish
        list so this can only get worse.

        Grep for things like term_cursor_move.

        (To be honest, I don't see anyone
        importing a new readline before 5.1 is
        out)

     o  tui.c:va_catch_errors() bitrot

        This nasty piece of work used knowledge
        of the internals of GDBs error functions :-(
        Ever since those internals were cleaned
        up this code has been broken. :-(

     o  tuiWin.c:c_makeVisibleWithNewHeight() broken
        tuiLayout.c:_extractDisplayStartAddr() broken

        Both these function call find_line_pc()
        incorrectly (wrong args, wrong return value).

        I suspect this bug has always been there!
        It had been hidden because those files
        didn't include the necessary header files
        from gdb proper :-(

     o  tuiRegs() host dependant

        Not suprisingly, this isn't a very portable
        section of code.  However, I'm sure people
        could live with no regs in the short to
        medium term.

     o  defs.h: #include "tui.h" et.al.

        I'm not sure where this came from.
        It was a really bad idea.

        To get things to compile I did a nasty
        hack (Just declare what was needed and
        replace any expressions like xx->y.z()
        in GDB proper with function calls).  I
        could commit it slightly cleaned up if
        you like.

        Medium Term. the #ifdef TUI and TuiDo()
        should be changed to hooks (like GDBTK).
        The gdb-events.[hc] is there for that
        purpose (1)

     o  tui.c:_tuiReset() host dependant

        tui.c contains a lump of termio[s]
        I suspect an equivalent block of
        code can be lifted from readline.
        An equivalent readline function may
        even be available.

     o  curses.h vs ncurses.h.

        Simple portability problem.

     o  subsetCompare()

        This function is a mystery - where is it?

     o  tui-file.[hc] cleanup

        This can be significantly simplified.

     o  The code should be pacified. (-Werror -W...)

        There are plenty of #includes,
        duplicate #includes, missing function decls
        and the like.

        Some of the problems I found were through
        fixing a few of the warnings.

     o  The code should be GNUtified.

        It would be very nice to have this code
        look like the rest of GDB.  That way people
        would be more accepting of it as a true
        gdb component.

        Until it is GNUtified it is going to stick
        out like a sore thumb to the programmer.

     o  The code should be clearly copyrighted

        (FSF, with due credit to HP)

--

Add support for ``gdb --- PROGRAM ARGS ...''.
Add support for ``gdb -cmd=...''

Along with many variations.  Check:

????? for a full discussion.

for a discussion.

--

Implement ``(gdb) !ls''.

Which is very different from ``(gdb) ! ls''.  Implementing the latter
is trivial.

http://sourceware.cygnus.com/ml/gdb/2000-q1/msg00034.html

--

Change the (char *list[]) to (const char (*)[]) so that dynamic lists can
be passed.

--

When tab expanding something like ``set arch<tab>'' ignore the
deprecated ``set archdebug'' and expand to ``set architecture''.

--

Replace the code that uses the host FPU with an emulator of the target
FPU.

--

The "ocd reset" command needs to flush the dcache, which requires breaking
the abstraction layer between the target independent and target code.  One
way to address this is provide a generic "reset" command and target vector.

http://sources.redhat.com/ml/gdb-patches/2000-10/msg00011.html

--

                        Thread Support
                        ==============

--

Generic: lin-thread cannot handle thread exit (Mark Kettenis, Michael
Snyder) http://sourceware.cygnus.com/ml/gdb/2000-q1/msg00525.html

The thread_db assisted debugging code doesn't handle exiting threads
properly, at least in combination with glibc 2.1.3 (the framework is
there, just not the actual code).  There are at least two problems
that prevent this from working.

As an additional reference point, the pre thread_db code did not work
either.

--

GNU/Linux/x86 and random thread signals (and Solaris/SPARC but not
Solaris/x86).
http://sourceware.cygnus.com/ml/gdb/2000-q1/msg00336.html

Christopher Blizzard writes:

So, I've done some more digging into this and it looks like Jim
Kingdon has reported this problem in the past:

http://sourceware.cygnus.com/ml/bug-gdb/1999-10/msg00058.html

I can reproduce this problem both with and without Tom's patch.  Has
anyone seen this before?  Maybe have a solution for it hanging around?
:)

There's a test case for this documented at:

when debugging threaded applications you get extra SIGTRAPs
http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=9565

[There should be a GDB testcase - cagney]

--

GDB5 TOT on unixware 7
http://sourceware.cygnus.com/ml/gdb/2000-04/msg00119.html

Robert Lipe writes:
> I just spun the top of tree of the GDB5 branch on UnixWare 7.  As a
> practical matter, the current thread support is somewhat more annoying
> than when GDB was thread-unaware.

--

                        Language Support
                        ================

New languages come onto the scene all the time.

--

Re: Various C++ things

value_headof/value_from_vtable_info are worthless, and should be
removed.  The one place in printcmd.c that uses it should use the RTTI
functions.

RTTI for g++ should be using the typeinfo functions rather than the
vtables.  The typeinfo functions are always at offset 4 from the
beginning of the vtable, and are always right. The vtables will have
weird names like E::VB sometimes.  The typeinfo function will always
be "E type_info function", or somesuch.

value_virtual_fn_field needs to be fixed so there are no failures for
virtual functions for C++ using g++.

Testsuite cases are the major priority right now for C++ support,
since i have to make a lot of changes that could potentially break
each other.

--

Add support for Modula3

Get DEC/Compaq to contribute their Modula-3 support.

--

                Remote Protocol Support
                =======================

--

Revised UDP support (was: Re: [Fwd: [patch] UDP transport support])
http://sourceware.cygnus.com/ml/gdb-patches/2000-04/msg00000.html

(Broken) support for GDB's remote protocol across UDP is to be
included in the follow-on release.

It should be noted that UDP can only work when the [Gg] packet fits in
a single UDP packet.

There is also much debate over the merit of this.

--

Migrate qfThreadInfo packet -> qThreadInfo. (Andrew Cagney)

Add support for packet enable/disable commands with these thread
packets.  General cleanup.

[PATCH] Document the ThreadInfo remote protocol queries
http://sourceware.cygnus.com/ml/gdb-patches/2000-q1/msg00832.html

[PATCH] "info threads" queries for remote.c
http://sourceware.cygnus.com/ml/gdb-patches/2000-q1/msg00831.html

--

Remote protocol doco feedback.

Too much feedback to mention needs to be merged in (901660).  Search
for the word ``remote''.


http://sourceware.cygnus.com/ml/gdb/2000-q1/msg00023.html
http://sourceware.cygnus.com/ml/gdb/2000-q1/msg00056.html
http://sourceware.cygnus.com/ml/gdb/2000-q1/msg00382.html

--

GDB doesn't recover gracefully from remote protocol errors.

GDB wasn't checking for NAKs from the remote target.  Instead a NAK is
ignored and a timeout is required before GDB retries.  A pre-cursor to
fixing this this is making GDB's remote protocol packet more robust.

While downloading to a remote protocol target, gdb ignores packet
errors in so far as it will continue to download with chunk N+1 even
if chunk N was not correctly sent.  This causes gdb.base/remote.exp to
take a painfully long time to run.  As a PS that test needs to be
fixed so that it builds on 16 bit machines.

--

Fix the ``!'' packet.

JT reported that the existing targets do, in fact return ``OK'' so it
is possible to merge remote and extended-remote targets.

--

Drop ``<address>'' from the [SsCc] packets.

I don't think that GDB generates them so having it in the protocol is
silly.

--

Fix doco on the ``q'' packet.

It has evolved into a generic RPC.  The notes should reflect this and,
perhaps, the ``Q'' packet can be deprecated.

The doco should mention that ``OK'' is a valid packet response.

The doco should explain why ``OK'' needs to be a valid packet
response.

--

Add the cycle step command.

http://sourceware.cygnus.com/ml/gdb/2000-q1/msg00237.html

--

Resolve how to scale things to support very large packets.

--

Resolve how to handle a target that changes things like its endianess
on the fly - should it be returned in the ``T'' packet?

Underlying problem is that the register file is target endian.  If the
target endianess changes gdb doesn't know.

Suggest encoding registers as NN!VALUE.

--

GDB should allow incomming packets to be larger than outgoing ones.  A
fully loaded T packet (containing all registers) can be very large -
definitly larger than a corresponding Gg packet.

--

                        Symbol Support
                        ==============

If / when GDB starts to support the debugging of multi-processor
(rather than multi-thread) applications the symtab code will need to
be updated a little so that several independent symbol tables are
active at a given time.

The other interesting change is a clarification of the exact meaning
of CORE_ADDR and that has had consequences for a few targets (that
were abusing that data type).

--

Investiagate ways of reducing memory.

--

Investigate ways of improving load time.

--

Get the d10v to use POINTER_TO_ADDRESS and ADDRESS_TO_POINTER.

Consequence of recent symtab clarification.  No marks for figuring out
who maintains the d10v.

--

Get the MIPS to correctly sign extend all address <-> pointer
conversions.

Consequence of recent symtab clarification.  No marks for figuring out
who maintains the MIPS.

--

GDB truncates 64 bit enums.

http://sourceware.cygnus.com/ml/gdb-patches/2000-06/msg00290.html

--

                        Testsuite Support
                        =================

There are never to many testcases.

--

Better thread testsuite.

--

Better C++ testsuite.

--

Look at adding a GDB specific testsuite directory so that white box
tests of key internals can be added (eg ui_file).

--

Separate out tests that involve the floating point (FP).

(Something for people brining up new targets).  FP and non-fp tests
are combined.  I think there should be set of basic tests that
exercise pure integer support and then a more expanded set that
exercise FP and FP/integer interactions.

As an example, the MIPS, for n32 as problems with passing FP's and
structs.  Since most inferior call tests include FP it is difficult to
determine of the integer tests are ok.

--

                Architectural Changes: General
                ==============================

These are harder than simple cleanups / fixes and, consequently
involve more work.  Typically an Architectural Change will be broken
down into a more digestible set of cleanups and fixes.

--

Cleanup software single step.

At present many targets implement software single step by directly
blatting memory (see rs6000-tdep.c).  Those targets should register
the applicable breakpoints using the breakpoint framework.  Perhaphs a
new internal breakpoint class ``step'' is needed.

--

Replace READ_FP() with FRAME_HANDLE().

READ_FP() is a hangover from the days of the vax when the ABI really
did have a frame pointer register.  Modern architectures typically
construct a virtual frame-handle from the stack pointer and various
other bits of string.

Unfortunately GDB still treats this synthetic FP register as though it
is real.  That in turn really confuses users (arm and ``print $fp'' VS
``info registers fp'').  The synthetic FP should be separated out of
the true register set presented to the user.

--

Register Cache Cleanup (below from Andrew Cagney)

I would depict the current register architecture as something like:

        High GDB  -->   Low GDB
            |              |
           \|/            \|/
            --- REG NR -----
                   |
    register + REGISTER_BYTE(reg_nr)
                   |
                  \|/
        -------------------------
        |  extern register[]    |
        -------------------------

where neither the high (valops.c et.al.) or low gdb (*-tdep.c) are
really clear on what mechanisms they should be using to manipulate that
buffer.   Further, much code assumes, dangerously, that registers are
contigious.  Having got mips-tdep.c to support multiple ABIs, believe
me, that is a bad assumption.  Finally, that register cache layout is
determined by the current remote/local target and _not_ the less
specific target ISA.  In fact, in many cases it is determined by the
somewhat arbitrary layout of the [gG] packets!


How I would like the register file to work is more like:


          High GDB
             |
            \|/
       pseudo reg-nr
             |
        map pseudo <->
        random cache
        bytes       
             |
            \|/
        ------------
        | register |
        |  cache   |
        ------------
            /|\
             |
        map random cache
        bytes to target
        dependent i-face
            /|\
             |
       target dependent
        such as [gG] packet
        or ptrace buffer

The main objectives being:

        o       a clear separation between the low
                level target and the high level GDB

        o       a mechanism that solves the general
                problem of register aliases, overlaps
                etc instead of treating them as optional
                extras that can be wedged in as an after
                thought (that is a reasonable description
                of the current code).

                Identify then solve the hard case and the
                rest just falls out.  GDB solved the easy
                case and then tried to ignore the real
                world :-)

        o       a removal of the assumption that the
                mapping between the register cache
                and virtual registers is largely static.
                If you flip the USR/SSR stack register
                select bit in the status-register then
                the corresponding stack registers should
                reflect the change.

        o       a mechanism that clearly separates the
                gdb internal register cache from any
                target (not architecture) dependent
                specifics such as [gG] packets.

Of course, like anything, it sounds good in theory.  In reality, it
would have to contend with many<->many relationships at both the
virt<->cache and cache<->target level.  For instance:

        virt<->cache
                Modifying an mmx register may involve
                scattering values across both FP and
                mmpx specific parts of a buffer

        cache<->target
                When writing back a SP it may need to
                both be written to both SP and USP.


Hmm,

Rather than let this like the last time it was discussed, just slip, I'm
first going to add this e-mail (+ references) to TODO.  I'd then like to
sketch out a broad strategy I think could get us there.


First thing I'd suggest is separating out the ``extern registers[]''
code so that we can at least identify what is using it.  At present
things are scattered across many files.  That way we can at least
pretend that there is a cache instead of a global array :-)

I'd then suggest someone putting up a proposal for the pseudo-reg /
high-level side interface so that code can be adopted to it.  For old
code, initially a blanket rename of write_register_bytes() to
deprecated_write_register_bytes() would help.

Following that would, finaly be the corresponding changes to the target.

--

Check that GDB can handle all BFD architectures (Andrew Cagney)

There should be a test that checks that BFD/GDB are in sync with
regard to architecture changes.  Something like a test that first
queries GDB for all supported architectures and then feeds each back
to GDB..  Anyone interested in learning how to write tests?  :-)

--

                Architectural Change: Multi-arch et al.
                =======================================

The long term objective is to remove all assumptions that there is a
single target with a single address space with a single instruction
set architecture and single application binary interface.

This is an ongoing effort.  The first milestone is to enable
``multi-arch'' where by all architectural decisions are made at
runtime.

It should be noted that ``gdbarch'' is really ``gdbabi'' and
``gdbisa''.  Once things are multi-arched breaking that down correctly
will become much easier.

--

GDBARCH cleanup (Andrew Cagney)

The non-generated parts of gdbarch.{sh,h,c} should be separated out
into arch-utils.[hc].

Document that gdbarch_init_ftype could easily fail because it didn't
identify an architecture.

--

Fix BELIEVE_PPC_PROMOTION.  Change it to BELIEVE_PPC_PROMOTION_P?

At present there is still #ifdef BELIEVE_PPC_PROMOTION code in the
symtab file.

--

Fix target_signal_from_host() etc.

The name is wrong for starters.  ``target_signal'' should probably be
``gdb_signal''.  ``from_host'' should be ``from_target_signal''.
After that it needs to be multi-arched and made independent of any
host signal numbering.

Once this is done, the signal enum can probably be moved to
include/gdb so that it is available to embedded stubs.

--

Update ALPHA so that it uses ``struct frame_extra_info'' instead of
EXTRA_FRAME_INFO.

This is a barrier to replacing mips_extra_func_info with something
that works with multi-arch.

--

Multi-arch  mips_extra_func_info.

This first needs the alpha to be updated so that it uses ``struct
frame_extra_info''.

--

Rationalize TARGET_SINGLE_FORMAT and TARGET_SINGLE_BIT et al.

Surely one of them is redundant.

--

Convert ALL architectures to MULTI-ARCH.

--

Select the initial multi-arch ISA / ABI based on --target or similar.

At present the default is based on what ever is first in the BFD
archures table.  It should be determined based on the ``--target=...''
name.

--

Make MIPS pure multi-arch.

It is only at the multi-arch enabled stage.

--

Truly multi-arch.

Enable the code to recognize --enable-targets=.... like BINUTILS does.

Can the tm.h and nm.h files be eliminated by multi-arch.

--

        Architectural Change: MI, LIBGDB and scripting languages
        ========================================================

See also architectural changes related to the event loop.  LIBGDB
can't be finished until there is a generic event loop being used by
all targets.

The long term objective is it to be possible to integrate GDB into
scripting languages.

--

Implement generic ``(gdb) commmand > file''

Once everything is going through ui_file it should be come fairly
easy.

http://sourceware.cygnus.com/ml/gdb/2000-04/msg00104.html

--

Replace gdb_stdtarg with gdb_targout (and possibly gdb_targerr).

gdb_stdtarg is easily confused with gdb_stdarg.

--

Extra ui_file methods - dump.

Very useful for whitebox testing.

--

Eliminate error_begin().

With ui_file, there is no need for the statefull error_begin ()
function.

--

Send normal output to gdb_stdout.
Send error messages to gdb_stderror.
Send debug and log output log gdb_stdlog.

GDB still contains many cases where (f)printf or printf_filtered () is
used when it should be sending the messages to gdb_stderror or
gdb_stdlog.  The thought of #defining printf to something has crossed
peoples minds ;-)

--

Re-do GDB's output pager.

GDB's output pager still relies on people correctly using *_filtered
for gdb_stdout and *_unfiltered for gdb_stdlog / gdb_stderr.
Hopefully, with all normal output going to gdb_stdout, the pager can
just look at the ui_file that the output is on and then use that to
decide what to do about paging.  Sounds good in theory.

--

Check/cleanup MI documentation.

The list of commands specified in the documentation needs to be
checked against the mi-cmds.c table in a mechanical way (so that they
two can be kept up-to-date).

--

Convert MI into libgdb

MI provides a text interface into what should be many of the libgdb
functions.  The implementation of those functions should be separated
into the MI interface and the functions proper.  Those functions being
moved to gdb/lib say.

--

Create libgdb.h

The first part can already be found in defs.h.

--

MI's input does not use buffering.

At present the MI interface reads raw characters of from an unbuffered
FD.  This is to avoid several nasty buffer/race conditions.  That code
should be changed so that it registers its self with the event loop
(on the input FD) and then push commands up to MI as they arrive.

The serial code already does this.

--

Make MI interface accessible from existing CLI.

--

Add a breakpoint-edit command to MI.

It would be similar to MI's breakpoint create but would apply to an
existing breakpoint.  It saves the need to delete/create breakpoints
when ever they are changed.

--

Add directory path to MI breakpoint.

That way the GUI's task of finding the file within which the
breakpoint was set is simplified.

--

Add a mechanism to reject certain expression classes to MI

There are situtations where you don't want GDB's expression
parser/evaluator to perform inferior function calls or variable
assignments.  A way of restricting the expression parser so that such
operations are not accepted would be very helpful.

--

Remove sideffects from libgdb breakpoint create function.

The user can use the CLI to create a breakpoint with partial
information - no file (gdb would use the file from the last
breakpoint).

The libgdb interface currently affects that environment which can lead
to confusion when a user is setting breakpoints via both the MI and
the CLI.

This is also a good example of how getting the CLI ``right'' will be
hard.

--

Move gdb_lasterr to ui_out?

The way GDB throws errors and records them needs a re-think.  ui_out
handles the correct output well.  It doesn't resolve what to do with
output / error-messages when things go wrong.

--

do_setshow_command contains a 1024 byte buffer.

The function assumes that there will never be any more than 1024 bytes
of enum.  It should use mem_file.

--

Should struct cmd_list_element . completer take the command as an
argument?

--

Should the bulk of top.c:line_completion_function() be moved to
command.[hc]?  complete_on_cmdlist() and complete_on_enums() could
then be made private.

--

top.c (execute_command): Should a command being valid when the target
is running be made an attribute (predicate) to the command rather than
an explicit set of tests.

--

top.c (execute_command): Should the bulk of this function be moved
into command.[hc] so that top.c doesn't grub around in the command
internals?

--

                Architectural Change: Async
                ===========================

While GDB uses an event loop when prompting the user for input.  That
event loop is not exploited by targets when they allow the target
program to continue.  Typically targets still block in (target_wait())
until the program again halts.

The closest a target comes to supporting full asynchronous mode are
the remote targets ``async'' and ``extended-async''.

--

Asynchronous expression evaluator

Inferior function calls hang GDB.

--

Fix implementation of  ``target xxx''.

At present when the user specifies ``target xxxx'', the CLI maps that
directly onto a target open method.  It is then assumed that the
target open method should do all sorts of complicated things as this
is the only chance it has.  Check how the various remote targets
duplicate the target operations.  Check also how the various targets
behave differently for purely arbitrary reasons.

What should happen is that ``target xxxx'' should call a generic
``target'' function and that should then co-ordinate the opening of
``xxxx''.  This becomes especially important when you're trying to
open an asynchronous target that may need to perform background tasks
as part of the ``attach'' phase.

Unfortunately, due to limitations in the old/creaking command.h
interface, that isn't possible.  The function being called isn't told
of the ``xxx'' or any other context information.

Consequently a precursor to fixing ``target xxxx'' is to clean up the
CLI code so that it passes to the callback function (attatched to a
command) useful information such as the actual command and a context
for that command.  Other changes such as making ``struct command''
opaque may also help.

See also:
http://sourceware.cygnus.com/ml/gdb-patches/2000-06/msg00062.html

--

Make "target xxx" command interruptible.

As things become async this becomes possible.  A target would start
the connect and then return control to the event loop.  A cntrl-c
would notify the target that the operation is to be abandoned and the
target code could respond.

--

Add a "suspend" subcommand of the "continue" command to suspend gdb
while continuing  execution of the subprocess.  Useful when you are
debugging servers and you want to dodge out and initiate a connection
to a server running under gdb.

[hey async!!]

--

                        TODO FAQ
                        ========

Frequently requested but not approved requests.

--

Eliminate unused argument warnings using ATTRIBUTE_UNUSED.

The benefits on this one are thought to be marginal - GDBs design
means that unused parameters are very common.  GCC 3.0 will also
include the option -Wno-unused-parameter which means that ``-Wall
-Wno-unused-parameters -Werror'' can be specified.

--



                        Legacy Wish List
                        ================

This list is not up to date, and opinions vary about the importance or
even desirability of some of the items.  If you do fix something, it
always pays to check the below.

--

@c This does not work (yet if ever).  FIXME.
@c @item --parse=@var{lang} @dots{}
@c Configure the @value{GDBN} expression parser to parse the listed languages.
@c @samp{all} configures @value{GDBN} for all supported languages.  To get a
@c list of all supported languages, omit the argument.  Without this
@c option, @value{GDBN} is configured to parse all supported languages.

--

START_INFERIOR_TRAPS_EXPECTED need never be defined to 2, since that
is its default value.  Clean this up.

--

It should be possible to use symbols from shared libraries before we know
exactly where the libraries will be loaded.  E.g. "b perror" before running
the program.  This could maybe be done as an extension of the "breakpoint
re-evaluation" after new symbols are loaded.

--

Make single_step() insert and remove breakpoints in one operation.

[If this is talking about having single_step() insert the breakpoints,
run the target then pull the breakpoints then it is wrong.  The
function has to return as control has to eventually be passed back to
the main event loop.]

--

Speed up single stepping by avoiding extraneous ptrace calls.

--

Speed up single stepping by not inserting and removing breakpoints
each time the inferior starts and stops.

Breakpoints should not be inserted and deleted all the time.  Only the
one(s) there should be removed when we have to step over one.  Support
breakpoints that don't have to be removed to step over them.

[this has resulted in numerous debates.  The issue isn't clear cut]

--

Provide "voodoo" debugging of core files.  This creates a zombie
process as a child of the debugger, and loads it up with the data,
stack, and regs of the core file.  This allows you to call functions
in the executable, to manipulate the data in the core file.

[you wish]

--

GDB reopens the source file on every line, as you "next" through it.

[still true? I've a memory of this being fixed]

--

Perhaps "i source" should take an argument like that of "list".

--

Remove "at 0xnnnn" from the "b foo" response, if `print address off' and if
it matches the source line indicated.

--

The prompt at end of screen should accept space as well as CR.

--

Backtrace should point out what the currently selected frame is, in
its display, perhaps showing "@3 foo (bar, ...)" or ">3 foo (bar,
...)" rather than "#3 foo (bar, ...)".

--

"i program" should work for core files, and display more info, like what
actually caused it to die.

--

"x/10i" should shorten the long name, if any, on subsequent lines.

--

"next" over a function that longjumps, never stops until next time you happen
to get to that spot by accident.  E.g. "n" over execute_command which has
an error.

--

"set zeroprint off", don't bother printing members of structs which
are entirely zero.  Useful for those big structs with few useful
members.

--

GDB does four ioctl's for every command, probably switching terminal modes
to/from inferior or for readline or something.

--

terminal_ours versus terminal_inferior: cache state.  Switch should be a noop
if the state is the same, too.

--

"i frame" shows wrong "arglist at" location, doesn't show where the args
should be found, only their actual values.

--

There should be a way for "set" commands to validate the new setting
before it takes effect.

--

"ena d" is ambiguous, why?  "ena delete" seems to think it is a command!

--

i line VAR produces "Line number not known for symbol ``var''.".  I
thought we were stashing that info now!

--

We should be able to write to random files at hex offsets like adb.

--

[elena - delete this]

Handle add_file with separate text, data, and bss addresses.  Maybe
handle separate addresses for each segment in the object file?

--

[Jimb/Elena delete this one]

Handle free_named_symtab to cope with multiply-loaded object files
in a dynamic linking environment.  Should remember the last copy loaded,
but not get too snowed if it finds references to the older copy.

--

[elena delete this also]

Remove all references to:
        text_offset
        data_offset
        text_data_start
        text_end
        exec_data_offset
        ...
now that we have BFD.  All remaining are in machine dependent files.

--

Re-organize help categories into things that tend to fit on a screen
and hang together.

--

Add in commands like ADB's for searching for patterns, etc.  We should
be able to examine and patch raw unsymboled binaries as well in gdb as
we can in adb.  (E.g. increase the timeout in /bin/login without source).

[actually, add ADB interface :-]

--

When doing "step" or "next", if a few lines of source are skipped between
the previous line and the current one, print those lines, not just the
last line of a multiline statement.

--

Handling of "&" address-of operator needs some serious overhaul
for ANSI C and consistency on arrays and functions.
  For "float point[15];":
ptype &point[4]   ==> Attempt to take address of non-lvalue.
  For "char *malloc();":
ptype malloc      ==> "char *()";  should be same as
ptype &malloc     ==> "char *(*)()"
call printf ("%x\n", malloc)   ==> weird value, should be same as
call printf ("%x\n", &malloc)  ==> correct value

--

Fix dbxread.c symbol reading in the presence of interrupts.  It
currently leaves a cleanup to blow away the entire symbol table when a
QUIT occurs.  (What's wrong with that? -kingdon, 28 Oct 1993).

[I suspect that the grype was that, on a slow system, you might want
to cntrl-c and get just half the symbols and then load the rest later
- scary to be honest]

--

Mipsread.c reads include files depth-first, because the dependencies
in the psymtabs are way too inclusive (it seems to me).  Figure out what
really depends on what, to avoid recursing 20 or 30 times while reading
real symtabs.

--

value_add() should be subtracting the lower bound of arrays, if known,
and possibly checking against the upper bound for error reporting.

--

When listing source lines, check for a preceding \n, to verify that
the file hasn't changed out from under us.

[fixed by some other means I think.  That hack wouldn't actually work
reliably - the file might move such that another \n appears. ]

--

Get all the remote systems (where the protocol allows it) to be able to
stop the remote system when the GDB user types ^C (like remote.c
does).  For ebmon, use ^Ak.

--

Possible feature: A version of the "disassemble" command which shows
both source and assembly code ("set symbol-filename on" is a partial
solution).

[has this been done?  It was certainly done for MI and GDBtk]

--

investigate "x/s 0" (right now stops early) (I think maybe GDB is
using a 0 address for bad purposes internally).

--

Make "info path" and path_command work again (but independent of the
environment either of gdb or that we'll pass to the inferior).

--

Make GDB understand the GCC feature for putting octal constants in
enums.  Make it so overflow on an enum constant does not error_type
the whole type.  Allow arbitrarily large enums with type attributes.
Put all this stuff in the testsuite.

--

Make TYPE_CODE_ERROR with a non-zero TYPE_LENGTH more useful (print
the value in hex; process type attributes).  Add this to the
testsuite.  This way future compilers can add new types and old
versions of GDB can do something halfway reasonable.

--

Fix mdebugread.c:parse_type to do fundamental types right (see
rs6000_builtin_type in stabsread.c for what "right" is--the point is
that the debug format fixes the sizes of these things and it shouldn't
depend on stuff like TARGET_PTR_BIT and so on.  For mdebug, there seem
to be separate bt* codes for 64 bit and 32 bit things, and GDB should
be aware of that).  Also use a switch statement for clarity and speed.

--

Investigate adding symbols in target_load--some targets do, some
don't.

--

Put dirname in psymtabs and change lookup*symtab to use dirname (so
/foo/bar.c works whether compiled by cc /foo/bar.c, or cd /foo; cc
bar.c).

--

Merge xcoffread.c and coffread.c.  Use breakpoint_re_set instead of
fixup_breakpoints.

--

Make a watchpoint which contains a function call an error (it is
broken now, making it work is probably not worth the effort).

--

New test case based on weird.exp but in which type numbers are not
renumbered (thus multiply defining a type).  This currently causes an
infinite loop on "p v_comb".

--

[Hey! Hint Hint Delete Delete!!!]

Fix 386 floating point so that floating point registers are real
registers (but code can deal at run-time if they are missing, like
mips and 68k).  This would clean up "info float" and related stuff.

--

gcc -g -c enummask.c then gdb enummask.o, then "p v".  GDB complains
about not being able to access memory location 0.

-------------------- enummask.c
enum mask
{
  ANIMAL = 0,
  VEGETABLE = 1,
  MINERAL = 2,
  BASIC_CATEGORY = 3,

  WHITE = 0,
  BLUE = 4,
  GREEN = 8,
  BLACK = 0xc,
  COLOR = 0xc,

  ALIVE = 0x10,

  LARGE = 0x20
} v;

--

If try to modify value in file with "set write off" should give
appropriate error not "cannot access memory at address 0x65e0".

--

Allow core file without exec file on RS/6000.

--

Make sure "shell" with no arguments works right on DOS.

--

Make gdb.ini (as well as .gdbinit) be checked on all platforms, so
the same directory can be NFS-mounted on unix or DOS, and work the
same way.

--

[Is this another delete???]

Get SECT_OFF_TEXT stuff out of objfile_relocate (might be needed to
get RS/6000 to work right, might not be immediately relevant).

--

Work out some kind of way to allow running the inferior to be done as
a sub-execution of, eg. breakpoint command lists.  Currently running
the inferior interupts any command list execution.  This would require
some rewriting of wait_for_inferior & friends, and hence should
probably be done in concert with the above.

--

Add function arguments to gdb user defined functions.

--

Add convenience variables that refer to exec file, symbol file,
selected frame source file, selected frame function, selected frame
line number, etc.

--

Modify the handling of symbols grouped through BINCL/EINCL stabs to
allocate a partial symtab for each BINCL/EINCL grouping.  This will
seriously decrease the size of inter-psymtab dependencies and hence
lessen the amount that needs to be read in when a new source file is
accessed. 

--

Add a command for searching memory, a la adb.  It specifies size,
mask, value, start address.  ADB searches until it finds it or hits
an error (or is interrupted).

--

Remove the range and type checking code and documentation, if not
going to implement.

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