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.
250 .struct symbol_cache_entry; {* Forward declaration *}
252 .typedef CONST struct reloc_howto_struct
254 . {* The type field has mainly a documetary use - the back end can
255 . to what it wants with it, though the normally the back end's
256 . external idea of what a reloc number would be would be stored
257 . in this field. For example, the a PC relative word relocation
258 . in a coff environment would have the type 023 - because that's
259 . what the outside world calls a R_PCRWORD reloc. *}
262 . {* The value the final relocation is shifted right by. This drops
263 . unwanted data from the relocation. *}
264 . unsigned int rightshift;
266 . {* The size of the item to be relocated - 0, is one byte, 1 is 2
267 . bytes, 3 is four bytes. *}
271 . unsigned int bitsize;
273 . {* Notes that the relocation is relative to the location in the
274 . data section of the addend. The relocation function will
275 . subtract from the relocation value the address of the location
276 . being relocated. *}
277 . boolean pc_relative;
280 . unsigned int bitpos;
285 . {* Causes the relocation routine to return an error if overflow
286 . is detected when relocating. *}
287 . boolean complain_on_overflow;
289 . {* If this field is non null, then the supplied function is
290 . called rather than the normal function. This allows really
291 . strange relocation methods to be accomodated (eg, i960 callj
293 . bfd_reloc_status_type EXFUN ((*special_function),
295 . arelent *reloc_entry,
296 . struct symbol_cache_entry *symbol,
298 . asection *input_section));
300 . {* The textual name of the relocation type. *}
303 . {* When performing a partial link, some formats must modify the
304 . relocations rather than the data - this flag signals this.*}
305 . boolean partial_inplace;
307 . {* The src_mask is used to select what parts of the read in data
308 . are to be used in the relocation sum. Eg, if this was an 8 bit
309 . bit of data which we read and relocated, this would be
310 . 0x000000ff. When we have relocs which have an addend, such as
311 . sun4 extended relocs, the value in the offset part of a
312 . relocating field is garbage so we never use it. In this case
313 . the mask would be 0x00000000. *}
316 . {* The dst_mask is what parts of the instruction are replaced
317 . into the instruction. In most cases src_mask == dst_mask,
318 . except in the above special case, where dst_mask would be
319 . 0x000000ff, and src_mask would be 0x00000000. *}
322 . {* When some formats create PC relative instructions, they leave
323 . the value of the pc of the place being relocated in the offset
324 . slot of the instruction, so that a PC relative relocation can
325 . be made just by adding in an ordinary offset (eg sun3 a.out).
326 . Some formats leave the displacement part of an instruction
327 . empty (eg m88k bcs), this flag signals the fact.*}
328 . boolean pcrel_offset;
339 The HOWTO define is horrible and will go away.
342 .#define HOWTO(C, R,S,B, P, BI, ABS, O, SF, NAME, INPLACE, MASKSRC, MASKDST, PC) \
343 . {(unsigned)C,R,S,B, P, BI, ABS,O,SF,NAME,INPLACE,MASKSRC,MASKDST,PC}
346 And will be replaced with the totally magic way. But for the
347 moment, we are compatible, so do it this way..
350 .#define NEWHOWTO( FUNCTION, NAME,SIZE,REL,IN) HOWTO(0,0,SIZE,0,REL,0,false,false,FUNCTION, NAME,false,0,0,IN)
353 Helper routine to turn a symbol into a relocation value.
355 .#define HOWTO_PREPARE(relocation, symbol) \
357 . if (symbol != (asymbol *)NULL) { \
358 . if (symbol->section == &bfd_com_section) { \
362 . relocation = symbol->value; \
375 How relocs are tied together
377 .typedef unsigned char bfd_byte;
379 .typedef struct relent_chain {
381 . struct relent_chain *next;
390 bfd_perform_relocation
393 bfd_reloc_status_type
394 bfd_perform_relocation
396 arelent *reloc_entry,
398 asection *input_section,
402 If an output_bfd is supplied to this function the generated
403 image will be relocatable, the relocations are copied to the
404 output file after they have been changed to reflect the new
405 state of the world. There are two ways of reflecting the
406 results of partial linkage in an output file; by modifying the
407 output data in place, and by modifying the relocation record.
408 Some native formats (eg basic a.out and basic coff) have no
409 way of specifying an addend in the relocation type, so the
410 addend has to go in the output data. This is no big deal
411 since in these formats the output data slot will always be big
412 enough for the addend. Complex reloc types with addends were
413 invented to solve just this problem.
418 bfd_reloc_status_type
419 DEFUN(bfd_perform_relocation,(abfd,
425 arelent *reloc_entry AND
427 asection *input_section AND
431 bfd_reloc_status_type flag = bfd_reloc_ok;
432 bfd_vma addr = reloc_entry->address ;
433 bfd_vma output_base = 0;
434 reloc_howto_type *howto = reloc_entry->howto;
435 asection *reloc_target_output_section ;
439 symbol = *( reloc_entry->sym_ptr_ptr);
440 if ((symbol->section == &bfd_abs_section)
441 && output_bfd != (bfd *)NULL)
443 reloc_entry->address += input_section->output_offset;
449 if ((symbol->section == &bfd_und_section) && output_bfd == (bfd *)NULL) {
450 flag = bfd_reloc_undefined;
453 if (howto->special_function){
454 bfd_reloc_status_type cont;
455 cont = howto->special_function(abfd,
460 if (cont != bfd_reloc_continue) return cont;
464 Work out which section the relocation is targetted at and the
465 initial relocation command value.
469 if (symbol->section == &bfd_com_section) {
473 relocation = symbol->value;
477 reloc_target_output_section = symbol->section->output_section;
479 if (output_bfd && howto->partial_inplace==false) {
483 output_base = reloc_target_output_section->vma;
487 relocation += output_base + symbol->section->output_offset;
490 relocation += reloc_entry->addend ;
493 if(reloc_entry->address > input_section->_cooked_size)
495 return bfd_reloc_outofrange;
499 if (howto->pc_relative == true)
502 Anything which started out as pc relative should end up that
505 There are two ways we can see a pcrel instruction. Sometimes
506 the pcrel displacement has been partially calculated, it
507 includes the distance from the start of the section to the
508 instruction in it (eg sun3), and sometimes the field is
509 totally blank - eg m88kbcs.
514 input_section->output_section->vma + input_section->output_offset;
516 if (howto->pcrel_offset == true) {
517 relocation -= reloc_entry->address;
522 if (output_bfd!= (bfd *)NULL) {
523 if ( howto->partial_inplace == false) {
525 This is a partial relocation, and we want to apply the relocation
526 to the reloc entry rather than the raw data. Modify the reloc
527 inplace to reflect what we now know.
529 reloc_entry->addend = relocation ;
530 reloc_entry->address += input_section->output_offset;
535 /* This is a partial relocation, but inplace, so modify the
538 If we've relocated with a symbol with a section, change
539 into a ref to the section belonging to the symbol
541 reloc_entry->addend = relocation ;
542 reloc_entry->address += input_section->output_offset;
550 reloc_entry->addend = 0;
556 Either we are relocating all the way, or we don't want to apply
557 the relocation to the reloc entry (probably because there isn't
558 any room in the output format to describe addends to relocs)
560 relocation >>= howto->rightshift;
562 /* Shift everything up to where it's going to be used */
564 relocation <<= howto->bitpos;
566 /* Wait for the day when all have the mask in them */
569 i instruction to be left alone
570 o offset within instruction
571 r relocation offset to apply
580 i i i i i o o o o o from bfd_get<size>
581 and S S S S S to get the size offset we want
582 + r r r r r r r r r r to get the final value to place
583 and D D D D D to chop to right size
584 -----------------------
587 ... i i i i i o o o o o from bfd_get<size>
588 and N N N N N get instruction
589 -----------------------
595 -----------------------
596 R R R R R R R R R R put into bfd_put<size>
600 x = ( (x & ~howto->dst_mask) | (((x & howto->src_mask) + relocation) & howto->dst_mask))
606 char x = bfd_get_8(abfd, (char *)data + addr);
608 bfd_put_8(abfd,x, (unsigned char *) data + addr);
614 short x = bfd_get_16(abfd, (bfd_byte *)data + addr);
616 bfd_put_16(abfd, x, (unsigned char *)data + addr);
621 long x = bfd_get_32(abfd, (bfd_byte *) data + addr);
623 bfd_put_32(abfd,x, (bfd_byte *)data + addr);
631 return bfd_reloc_other;
641 howto manager, , typedef arelent, Relocations
646 When an application wants to create a relocation, but doesn't
647 know what the target machine might call it, it can find out by
648 using this bit of code.
657 The insides of a reloc code
661 .typedef enum bfd_reloc_code_real
663 . {* 16 bits wide, simple reloc *}
666 . {* 8 bits wide, but used to form an address like 0xffnn *}
669 . {* 8 bits wide, simple *}
672 . {* 8 bits wide, pc relative *}
675 . {* The type of reloc used to build a contructor table - at the
676 . moment probably a 32 bit wide abs address, but the cpu can
680 . } bfd_reloc_code_real_type;
687 bfd_reloc_type_lookup
690 CONST struct reloc_howto_struct *
691 bfd_reloc_type_lookup
692 (CONST bfd_arch_info_type *arch, bfd_reloc_code_type code);
695 This routine returns a pointer to a howto struct which when
696 invoked, will perform the supplied relocation on data from the
702 CONST struct reloc_howto_struct *
703 DEFUN(bfd_reloc_type_lookup,(arch, code),
704 CONST bfd_arch_info_type *arch AND
705 bfd_reloc_code_type code)
707 return arch->reloc_type_lookup(arch, code);
710 static reloc_howto_type bfd_howto_32 =
711 HOWTO(0, 00,2,32,false,0,false,true,0,"VRT32", false,0xffffffff,0xffffffff,true);
716 bfd_default_reloc_type_lookup
719 CONST struct reloc_howto_struct *bfd_default_reloc_type_lookup
720 (CONST struct bfd_arch_info *,
721 bfd_reloc_code_type code);
724 Provides a default relocation lookuperer for any architectue
728 CONST struct reloc_howto_struct *
729 DEFUN(bfd_default_reloc_type_lookup,(arch, code),
730 CONST struct bfd_arch_info *arch AND
731 bfd_reloc_code_type code)
736 /* The type of reloc used in a ctor, which will be as wide as the
737 address - so either a 64, 32, or 16 bitter.. */
738 switch (arch->bits_per_address) {
742 return &bfd_howto_32;
751 return (struct reloc_howto_struct *)NULL;
757 bfd_generic_relax_section
760 boolean bfd_generic_relax_section
766 Provides default handling for relaxing for back ends which
767 don't do relaxing - ie does nothing
771 DEFUN(bfd_generic_relax_section,(abfd, section, symbols),
773 asection *section AND
784 bfd_generic_get_relocated_section_contents
788 bfd_generic_get_relocated_section_contents(bfd *abfd,
789 struct bfd_seclet_struct *seclet)
792 Provides default handling of relocation effort for back ends
793 which can't be bothered to do it efficiently.
798 DEFUN(bfd_generic_get_relocated_section_contents,(abfd, seclet),
800 struct bfd_seclet_struct *seclet)
802 extern bfd_error_vector_type bfd_error_vector;
804 /* Get enough memory to hold the stuff */
805 bfd *input_bfd = seclet->u.indirect.section->owner;
806 asection *input_section = seclet->u.indirect.section;
808 bfd_byte *data = (bfd_byte *) bfd_xmalloc(input_section->_raw_size);
810 bfd_size_type reloc_size = bfd_get_reloc_upper_bound(input_bfd,
812 arelent **reloc_vector = (arelent **) bfd_xmalloc(reloc_size);
814 /* read in the section */
815 bfd_get_section_contents(input_bfd,
819 input_section->_raw_size);
821 /* We're not relaxing the section, so just copy the size info */
822 input_section->_cooked_size = input_section->_raw_size;
823 input_section->reloc_done = true;
826 if (bfd_canonicalize_reloc(input_bfd,
829 seclet->u.indirect.symbols) )
832 for (parent = reloc_vector; * parent != (arelent *)NULL;
835 bfd_reloc_status_type r=
836 bfd_perform_relocation(input_bfd,
842 if (r != bfd_reloc_ok)
846 case bfd_reloc_undefined:
847 bfd_error_vector.undefined_symbol(*parent, seclet);
849 case bfd_reloc_dangerous:
850 bfd_error_vector.reloc_dangerous(*parent, seclet);
852 case bfd_reloc_outofrange:
853 case bfd_reloc_overflow:
854 bfd_error_vector.reloc_value_truncated(*parent, seclet);
865 free((char *)reloc_vector);