1 /* BFD support for handling relocation entries.
2 Copyright (C) 1990-1991 Free Software Foundation, Inc.
3 Written by Cygnus Support.
5 This file is part of BFD, the Binary File Descriptor library.
7 This program is free software; you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation; either version 2 of the License, or
10 (at your option) any later version.
12 This program is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program; if not, write to the Free Software
19 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */
25 BFD maintains relocations in much the same was as it maintains
26 symbols; they are left alone until required, then read in
27 en-mass and traslated into an internal form. There is a common
28 routine <<bfd_perform_relocation>> which acts upon the
29 canonical form to to the actual fixup.
31 Note that relocations are maintained on a per section basis,
32 whilst symbols are maintained on a per BFD basis.
34 All a back end has to do to fit the BFD interface is to create
35 as many <<struct reloc_cache_entry>> as there are relocations
36 in a particuar section, and fill in the right bits:
50 typedef arelent, howto manager, Relocations, Relocations
55 This is the structure of a relocation entry:
59 .typedef enum bfd_reloc_status
61 . {* No errors detected *}
64 . {* The relocation was performed, but there was an overflow. *}
67 . {* The address to relocate was not within the section supplied*}
68 . bfd_reloc_outofrange,
70 . {* Used by special functions *}
74 . bfd_reloc_notsupported,
76 . {* Unsupported relocation size requested. *}
79 . {* The symbol to relocate against was undefined.*}
80 . bfd_reloc_undefined,
82 . {* The relocation was performed, but may not be ok - presently
83 . generated only when linking i960 coff files with i960 b.out
87 . bfd_reloc_status_type;
90 .typedef struct reloc_cache_entry
92 . {* A pointer into the canonical table of pointers *}
93 . struct symbol_cache_entry **sym_ptr_ptr;
95 . {* offset in section *}
96 . rawdata_offset address;
98 . {* addend for relocation value *}
101 . {* Pointer to how to perform the required relocation *}
102 . CONST struct reloc_howto_struct *howto;
111 Here is a description of each of the fields within a relent:
115 The symbol table pointer points to a pointer to the symbol
116 associated with the relocation request. This would naturally
117 be the pointer into the table returned by the back end's
118 get_symtab action. @xref{Symbols}. The symbol is referenced
119 through a pointer to a pointer so that tools like the linker
120 can fix up all the symbols of the same name by modifying only
121 one pointer. The relocation routine looks in the symbol and
122 uses the base of the section the symbol is attached to and the
123 value of the symbol as the initial relocation offset. If the
124 symbol pointer is zero, then the section provided is looked up.
128 The address field gives the offset in bytes from the base of
129 the section data which owns the relocation record to the first
130 byte of relocatable information. The actual data relocated
131 will be relative to this point - for example, a relocation
132 type which modifies the bottom two bytes of a four byte word
133 would not touch the first byte pointed to in a big endian
134 world. @item addend The addend is a value provided by the back
135 end to be added (!) to the relocation offset. Its
136 interpretation is dependent upon the howto. For example, on
143 | return foo[0x12345678];
146 Could be compiled into:
149 | moveb @@#12345678,d0
155 This could create a reloc pointing to foo, but leave the
156 offset in the data (something like)
159 |RELOCATION RECORDS FOR [.text]:
163 |00000000 4e56 fffc ; linkw fp,#-4
164 |00000004 1039 1234 5678 ; moveb @@#12345678,d0
165 |0000000a 49c0 ; extbl d0
166 |0000000c 4e5e ; unlk fp
170 Using coff and an 88k, some instructions don't have enough
171 space in them to represent the full address range, and
172 pointers have to be loaded in two parts. So you'd get something like:
175 | or.u r13,r0,hi16(_foo+0x12345678)
176 | ld.b r2,r13,lo16(_foo+0x12345678)
180 This whould create two relocs, both pointing to _foo, and with
181 0x12340000 in their addend field. The data would consist of:
184 |RELOCATION RECORDS FOR [.text]:
186 |00000002 HVRT16 _foo+0x12340000
187 |00000006 LVRT16 _foo+0x12340000
189 |00000000 5da05678 ; or.u r13,r0,0x5678
190 |00000004 1c4d5678 ; ld.b r2,r13,0x5678
191 |00000008 f400c001 ; jmp r1
194 The relocation routine digs out the value from the data, adds
195 it to the addend to get the original offset and then adds the
196 value of _foo. Note that all 32 bits have to be kept around
197 somewhere, to cope with carry from bit 15 to bit 16.
199 On further example is the sparc and the a.out format. The
200 sparc has a similar problem to the 88k, in that some
201 instructions don't have room for an entire offset, but on the
202 sparc the parts are created odd sized lumps. The designers of
203 the a.out format chose not to use the data within the section
204 for storing part of the offset; all the offset is kept within
205 the reloc. Any thing in the data should be ignored.
208 | sethi %hi(_foo+0x12345678),%g2
209 | ldsb [%g2+%lo(_foo+0x12345678)],%i0
213 Both relocs contains a pointer to foo, and the offsets would
217 |RELOCATION RECORDS FOR [.text]:
219 |00000004 HI22 _foo+0x12345678
220 |00000008 LO10 _foo+0x12345678
222 |00000000 9de3bf90 ; save %sp,-112,%sp
223 |00000004 05000000 ; sethi %hi(_foo+0),%g2
224 |00000008 f048a000 ; ldsb [%g2+%lo(_foo+0)],%i0
225 |0000000c 81c7e008 ; ret
226 |00000010 81e80000 ; restore
231 The howto field can be imagined as a
232 relocation instruction. It is a pointer to a struct which
233 contains information on what to do with all the other
234 information in the reloc record and data section. A back end
235 would normally have a relocation instruction set and turn
236 relocations into pointers to the correct structure on input -
237 but it would be possible to create each howto field on demand.
246 The <<reloc_howto_type>> is a structure which contains all the
247 information that BFD needs to know to tie up a back end's data.
251 .typedef CONST struct reloc_howto_struct
253 . {* The type field has mainly a documetary use - the back end can
254 . to what it wants with it, though the normally the back end's
255 . external idea of what a reloc number would be would be stored
256 . in this field. For example, the a PC relative word relocation
257 . in a coff environment would have the type 023 - because that's
258 . what the outside world calls a R_PCRWORD reloc. *}
261 . {* The value the final relocation is shifted right by. This drops
262 . unwanted data from the relocation. *}
263 . unsigned int rightshift;
265 . {* The size of the item to be relocated - 0, is one byte, 1 is 2
266 . bytes, 3 is four bytes. *}
270 . unsigned int bitsize;
272 . {* Notes that the relocation is relative to the location in the
273 . data section of the addend. The relocation function will
274 . subtract from the relocation value the address of the location
275 . being relocated. *}
276 . boolean pc_relative;
279 . unsigned int bitpos;
284 . {* Causes the relocation routine to return an error if overflow
285 . is detected when relocating. *}
286 . boolean complain_on_overflow;
288 . {* If this field is non null, then the supplied function is
289 . called rather than the normal function. This allows really
290 . strange relocation methods to be accomodated (eg, i960 callj
292 . bfd_reloc_status_type (*special_function)();
294 . {* The textual name of the relocation type. *}
297 . {* When performing a partial link, some formats must modify the
298 . relocations rather than the data - this flag signals this.*}
299 . boolean partial_inplace;
301 . {* The src_mask is used to select what parts of the read in data
302 . are to be used in the relocation sum. Eg, if this was an 8 bit
303 . bit of data which we read and relocated, this would be
304 . 0x000000ff. When we have relocs which have an addend, such as
305 . sun4 extended relocs, the value in the offset part of a
306 . relocating field is garbage so we never use it. In this case
307 . the mask would be 0x00000000. *}
310 . {* The dst_mask is what parts of the instruction are replaced
311 . into the instruction. In most cases src_mask == dst_mask,
312 . except in the above special case, where dst_mask would be
313 . 0x000000ff, and src_mask would be 0x00000000. *}
316 . {* When some formats create PC relative instructions, they leave
317 . the value of the pc of the place being relocated in the offset
318 . slot of the instruction, so that a PC relative relocation can
319 . be made just by adding in an ordinary offset (eg sun3 a.out).
320 . Some formats leave the displacement part of an instruction
321 . empty (eg m88k bcs), this flag signals the fact.*}
322 . boolean pcrel_offset;
333 The HOWTO define is horrible and will go away.
336 .#define HOWTO(C, R,S,B, P, BI, ABS, O, SF, NAME, INPLACE, MASKSRC, MASKDST, PC) \
337 . {(unsigned)C,R,S,B, P, BI, ABS,O,SF,NAME,INPLACE,MASKSRC,MASKDST,PC}
340 And will be replaced with the totally magic way. But for the
341 moment, we are compatible, so do it this way..
344 .#define NEWHOWTO( FUNCTION, NAME,SIZE,REL,IN) HOWTO(0,0,SIZE,0,REL,0,false,false,FUNCTION, NAME,false,0,0,IN)
347 Helper routine to turn a symbol into a relocation value.
349 .#define HOWTO_PREPARE(relocation, symbol) \
351 . if (symbol != (asymbol *)NULL) { \
352 . if (symbol->section == &bfd_com_section) { \
356 . relocation = symbol->value; \
369 How relocs are tied together
371 .typedef unsigned char bfd_byte;
373 .typedef struct relent_chain {
375 . struct relent_chain *next;
384 bfd_perform_relocation
387 bfd_reloc_status_type
388 bfd_perform_relocation
390 arelent *reloc_entry,
392 asection *input_section,
396 If an output_bfd is supplied to this function the generated
397 image will be relocatable, the relocations are copied to the
398 output file after they have been changed to reflect the new
399 state of the world. There are two ways of reflecting the
400 results of partial linkage in an output file; by modifying the
401 output data in place, and by modifying the relocation record.
402 Some native formats (eg basic a.out and basic coff) have no
403 way of specifying an addend in the relocation type, so the
404 addend has to go in the output data. This is no big deal
405 since in these formats the output data slot will always be big
406 enough for the addend. Complex reloc types with addends were
407 invented to solve just this problem.
412 bfd_reloc_status_type
413 DEFUN(bfd_perform_relocation,(abfd,
419 arelent *reloc_entry AND
421 asection *input_section AND
425 bfd_reloc_status_type flag = bfd_reloc_ok;
426 bfd_vma addr = reloc_entry->address ;
427 bfd_vma output_base = 0;
428 reloc_howto_type *howto = reloc_entry->howto;
429 asection *reloc_target_output_section ;
433 symbol = *( reloc_entry->sym_ptr_ptr);
434 if ((symbol->section == &bfd_und_section) && output_bfd == (bfd *)NULL) {
435 flag = bfd_reloc_undefined;
438 if (howto->special_function){
439 bfd_reloc_status_type cont;
440 cont = howto->special_function(abfd,
445 if (cont != bfd_reloc_continue) return cont;
449 Work out which section the relocation is targetted at and the
450 initial relocation command value.
454 if (symbol->section == &bfd_com_section) {
458 relocation = symbol->value;
462 reloc_target_output_section = symbol->section->output_section;
464 if (output_bfd && howto->partial_inplace==false) {
468 output_base = reloc_target_output_section->vma;
472 relocation += output_base + symbol->section->output_offset;
475 relocation += reloc_entry->addend ;
478 if(reloc_entry->address > input_section->_cooked_size)
480 return bfd_reloc_outofrange;
484 if (howto->pc_relative == true)
487 Anything which started out as pc relative should end up that
490 There are two ways we can see a pcrel instruction. Sometimes
491 the pcrel displacement has been partially calculated, it
492 includes the distance from the start of the section to the
493 instruction in it (eg sun3), and sometimes the field is
494 totally blank - eg m88kbcs.
499 input_section->output_section->vma + input_section->output_offset;
501 if (howto->pcrel_offset == true) {
502 relocation -= reloc_entry->address;
507 if (output_bfd!= (bfd *)NULL) {
508 if ( howto->partial_inplace == false) {
510 This is a partial relocation, and we want to apply the relocation
511 to the reloc entry rather than the raw data. Modify the reloc
512 inplace to reflect what we now know.
514 reloc_entry->addend = relocation ;
515 reloc_entry->address += input_section->output_offset;
520 /* This is a partial relocation, but inplace, so modify the
523 If we've relocated with a symbol with a section, change
524 into a ref to the section belonging to the symbol
526 reloc_entry->addend = relocation ;
527 reloc_entry->address += input_section->output_offset;
535 reloc_entry->addend = 0;
541 Either we are relocating all the way, or we don't want to apply
542 the relocation to the reloc entry (probably because there isn't
543 any room in the output format to describe addends to relocs)
545 relocation >>= howto->rightshift;
547 /* Shift everything up to where it's going to be used */
549 relocation <<= howto->bitpos;
551 /* Wait for the day when all have the mask in them */
554 i instruction to be left alone
555 o offset within instruction
556 r relocation offset to apply
565 i i i i i o o o o o from bfd_get<size>
566 and S S S S S to get the size offset we want
567 + r r r r r r r r r r to get the final value to place
568 and D D D D D to chop to right size
569 -----------------------
572 ... i i i i i o o o o o from bfd_get<size>
573 and N N N N N get instruction
574 -----------------------
580 -----------------------
581 R R R R R R R R R R put into bfd_put<size>
585 x = ( (x & ~howto->dst_mask) | (((x & howto->src_mask) + relocation) & howto->dst_mask))
591 char x = bfd_get_8(abfd, (char *)data + addr);
593 bfd_put_8(abfd,x, (unsigned char *) data + addr);
599 short x = bfd_get_16(abfd, (bfd_byte *)data + addr);
601 bfd_put_16(abfd, x, (unsigned char *)data + addr);
606 long x = bfd_get_32(abfd, (bfd_byte *) data + addr);
608 bfd_put_32(abfd,x, (bfd_byte *)data + addr);
616 return bfd_reloc_other;
626 howto manager, , typedef arelent, Relocations
631 When an application wants to create a relocation, but doesn't
632 know what the target machine might call it, it can find out by
633 using this bit of code.
642 The insides of a reloc code
646 .typedef enum bfd_reloc_code_real
648 . {* 16 bits wide, simple reloc *}
651 . {* 8 bits wide, but used to form an address like 0xffnn *}
654 . {* 8 bits wide, simple *}
657 . {* 8 bits wide, pc relative *}
660 . {* The type of reloc used to build a contructor table - at the
661 . moment probably a 32 bit wide abs address, but the cpu can
665 . } bfd_reloc_code_real_type;
672 bfd_reloc_type_lookup
675 CONST struct reloc_howto_struct *
676 bfd_reloc_type_lookup
677 (CONST bfd_arch_info_type *arch, bfd_reloc_code_type code);
680 This routine returns a pointer to a howto struct which when
681 invoked, will perform the supplied relocation on data from the
687 CONST struct reloc_howto_struct *
688 DEFUN(bfd_reloc_type_lookup,(arch, code),
689 CONST bfd_arch_info_type *arch AND
690 bfd_reloc_code_type code)
692 return arch->reloc_type_lookup(arch, code);
695 static reloc_howto_type bfd_howto_32 =
696 HOWTO(0, 00,2,32,false,0,false,true,0,"VRT32", false,0xffffffff,0xffffffff,true);
701 bfd_default_reloc_type_lookup
704 CONST struct reloc_howto_struct *bfd_default_reloc_type_lookup
705 (CONST struct bfd_arch_info *,
706 bfd_reloc_code_type code);
709 Provides a default relocation lookuperer for any architectue
713 CONST struct reloc_howto_struct *
714 DEFUN(bfd_default_reloc_type_lookup,(arch, code),
715 CONST struct bfd_arch_info *arch AND
716 bfd_reloc_code_type code)
721 /* The type of reloc used in a ctor, which will be as wide as the
722 address - so either a 64, 32, or 16 bitter.. */
723 switch (arch->bits_per_address) {
727 return &bfd_howto_32;
736 return (struct reloc_howto_struct *)NULL;
742 bfd_generic_relax_section
745 boolean bfd_generic_relax_section
749 struct bfd_seclet_struct *seclet);
752 Provides default handling for relaxing for back ends which
753 don't do relaxing - ie does nothing
757 DEFUN(bfd_generic_relax_section,(abfd, section, symbols, seclet),
759 asection *section AND
760 asymbol **symbols AND
761 struct bfd_seclet_struct *seclet)
771 bfd_generic_get_relocated_section_contents
775 bfd_generic_get_relocated_section_contents(bfd *abfd,
776 struct bfd_seclet_struct *seclet)
779 Provides default handling of relocation effort for back ends
780 which can't be bothered to do it efficiently.
785 DEFUN(bfd_generic_get_relocated_section_contents,(abfd, seclet),
787 struct bfd_seclet_struct *seclet)
789 extern bfd_error_vector_type bfd_error_vector;
792 asymbol **symbols = 0;
794 /* Get enough memory to hold the stuff */
795 bfd *input_bfd = seclet->u.indirect.section->owner;
796 asection *input_section = seclet->u.indirect.section;
798 bfd_byte *data = (bfd_byte *)malloc(input_section->_raw_size);
799 bfd_byte *dst = data;
800 bfd_byte *prev_dst = data;
801 unsigned int gap = 0;
803 bfd_size_type reloc_size = bfd_get_reloc_upper_bound(input_bfd,
805 arelent **reloc_vector = (arelent **)malloc(reloc_size);
807 /* read in the section */
808 bfd_get_section_contents(input_bfd,
812 input_section->_raw_size);
814 /* We're not relaxing the section, so just copy the size info */
815 input_section->_cooked_size = input_section->_raw_size;
816 input_section->reloc_done = true;
819 if (bfd_canonicalize_reloc(input_bfd,
822 seclet->u.indirect.symbols) )
825 for (parent = reloc_vector; * parent != (arelent *)NULL;
828 bfd_reloc_status_type r=
829 bfd_perform_relocation(input_bfd,
835 if (r != bfd_reloc_ok)
841 case bfd_reloc_undefined:
842 bfd_error_vector.undefined_symbol(*parent, seclet);
844 case bfd_reloc_dangerous:
845 bfd_error_vector.reloc_dangerous(*parent, seclet);
847 case bfd_reloc_outofrange:
848 case bfd_reloc_overflow:
849 bfd_error_vector.reloc_value_truncated(*parent, seclet);
860 free((char *)reloc_vector);