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:
51 typedef arelent, howto manager, Relocations, Relocations
56 This is the structure of a relocation entry:
60 .typedef enum bfd_reloc_status
62 . {* No errors detected *}
65 . {* The relocation was performed, but there was an overflow. *}
68 . {* The address to relocate was not within the section supplied*}
69 . bfd_reloc_outofrange,
71 . {* Used by special functions *}
75 . bfd_reloc_notsupported,
77 . {* Unsupported relocation size requested. *}
80 . {* The symbol to relocate against was undefined.*}
81 . bfd_reloc_undefined,
83 . {* The relocation was performed, but may not be ok - presently
84 . generated only when linking i960 coff files with i960 b.out
88 . bfd_reloc_status_type;
91 .typedef struct reloc_cache_entry
93 . {* A pointer into the canonical table of pointers *}
94 . struct symbol_cache_entry **sym_ptr_ptr;
96 . {* offset in section *}
97 . rawdata_offset address;
99 . {* addend for relocation value *}
102 . {* Pointer to how to perform the required relocation *}
103 . CONST struct reloc_howto_struct *howto;
112 Here is a description of each of the fields within a relent:
116 The symbol table pointer points to a pointer to the symbol
117 associated with the relocation request. This would naturally
118 be the pointer into the table returned by the back end's
119 get_symtab action. @xref{Symbols}. The symbol is referenced
120 through a pointer to a pointer so that tools like the linker
121 can fix up all the symbols of the same name by modifying only
122 one pointer. The relocation routine looks in the symbol and
123 uses the base of the section the symbol is attached to and the
124 value of the symbol as the initial relocation offset. If the
125 symbol pointer is zero, then the section provided is looked up.
129 The address field gives the offset in bytes from the base of
130 the section data which owns the relocation record to the first
131 byte of relocatable information. The actual data relocated
132 will be relative to this point - for example, a relocation
133 type which modifies the bottom two bytes of a four byte word
134 would not touch the first byte pointed to in a big endian
139 The addend is a value provided by the back end to be added (!)
140 to the relocation offset. Its interpretation is dependent upon
141 the howto. For example, on the 68k the code:
147 | return foo[0x12345678];
150 Could be compiled into:
153 | moveb @@#12345678,d0
159 This could create a reloc pointing to foo, but leave the
160 offset in the data (something like)
163 |RELOCATION RECORDS FOR [.text]:
167 |00000000 4e56 fffc ; linkw fp,#-4
168 |00000004 1039 1234 5678 ; moveb @@#12345678,d0
169 |0000000a 49c0 ; extbl d0
170 |0000000c 4e5e ; unlk fp
174 Using coff and an 88k, some instructions don't have enough
175 space in them to represent the full address range, and
176 pointers have to be loaded in two parts. So you'd get something like:
179 | or.u r13,r0,hi16(_foo+0x12345678)
180 | ld.b r2,r13,lo16(_foo+0x12345678)
184 This whould create two relocs, both pointing to _foo, and with
185 0x12340000 in their addend field. The data would consist of:
188 |RELOCATION RECORDS FOR [.text]:
190 |00000002 HVRT16 _foo+0x12340000
191 |00000006 LVRT16 _foo+0x12340000
193 |00000000 5da05678 ; or.u r13,r0,0x5678
194 |00000004 1c4d5678 ; ld.b r2,r13,0x5678
195 |00000008 f400c001 ; jmp r1
198 The relocation routine digs out the value from the data, adds
199 it to the addend to get the original offset and then adds the
200 value of _foo. Note that all 32 bits have to be kept around
201 somewhere, to cope with carry from bit 15 to bit 16.
203 On further example is the sparc and the a.out format. The
204 sparc has a similar problem to the 88k, in that some
205 instructions don't have room for an entire offset, but on the
206 sparc the parts are created odd sized lumps. The designers of
207 the a.out format chose not to use the data within the section
208 for storing part of the offset; all the offset is kept within
209 the reloc. Any thing in the data should be ignored.
212 | sethi %hi(_foo+0x12345678),%g2
213 | ldsb [%g2+%lo(_foo+0x12345678)],%i0
217 Both relocs contains a pointer to foo, and the offsets would
221 |RELOCATION RECORDS FOR [.text]:
223 |00000004 HI22 _foo+0x12345678
224 |00000008 LO10 _foo+0x12345678
226 |00000000 9de3bf90 ; save %sp,-112,%sp
227 |00000004 05000000 ; sethi %hi(_foo+0),%g2
228 |00000008 f048a000 ; ldsb [%g2+%lo(_foo+0)],%i0
229 |0000000c 81c7e008 ; ret
230 |00000010 81e80000 ; restore
235 The howto field can be imagined as a
236 relocation instruction. It is a pointer to a struct which
237 contains information on what to do with all the other
238 information in the reloc record and data section. A back end
239 would normally have a relocation instruction set and turn
240 relocations into pointers to the correct structure on input -
241 but it would be possible to create each howto field on demand.
250 The <<reloc_howto_type>> is a structure which contains all the
251 information that BFD needs to know to tie up a back end's data.
254 .struct symbol_cache_entry; {* Forward declaration *}
256 .typedef CONST struct reloc_howto_struct
258 . {* The type field has mainly a documetary use - the back end can
259 . to what it wants with it, though the normally the back end's
260 . external idea of what a reloc number would be would be stored
261 . in this field. For example, the a PC relative word relocation
262 . in a coff environment would have the type 023 - because that's
263 . what the outside world calls a R_PCRWORD reloc. *}
266 . {* The value the final relocation is shifted right by. This drops
267 . unwanted data from the relocation. *}
268 . unsigned int rightshift;
270 . {* The size of the item to be relocated - 0, is one byte, 1 is 2
271 . bytes, 3 is four bytes. A -ve value indicates that the
272 . result is to be subtracted from the data*}
276 . unsigned int bitsize;
278 . {* Notes that the relocation is relative to the location in the
279 . data section of the addend. The relocation function will
280 . subtract from the relocation value the address of the location
281 . being relocated. *}
282 . boolean pc_relative;
285 . unsigned int bitpos;
290 . {* Causes the relocation routine to return an error if overflow
291 . is detected when relocating. *}
292 . boolean complain_on_overflow;
294 . {* If this field is non null, then the supplied function is
295 . called rather than the normal function. This allows really
296 . strange relocation methods to be accomodated (eg, i960 callj
298 . bfd_reloc_status_type (*special_function)
299 . PARAMS ((bfd *abfd,
300 . arelent *reloc_entry,
301 . struct symbol_cache_entry *symbol,
303 . asection *input_section,
306 . {* The textual name of the relocation type. *}
309 . {* When performing a partial link, some formats must modify the
310 . relocations rather than the data - this flag signals this.*}
311 . boolean partial_inplace;
313 . {* The src_mask is used to select what parts of the read in data
314 . are to be used in the relocation sum. Eg, if this was an 8 bit
315 . bit of data which we read and relocated, this would be
316 . 0x000000ff. When we have relocs which have an addend, such as
317 . sun4 extended relocs, the value in the offset part of a
318 . relocating field is garbage so we never use it. In this case
319 . the mask would be 0x00000000. *}
322 . {* The dst_mask is what parts of the instruction are replaced
323 . into the instruction. In most cases src_mask == dst_mask,
324 . except in the above special case, where dst_mask would be
325 . 0x000000ff, and src_mask would be 0x00000000. *}
328 . {* When some formats create PC relative instructions, they leave
329 . the value of the pc of the place being relocated in the offset
330 . slot of the instruction, so that a PC relative relocation can
331 . be made just by adding in an ordinary offset (eg sun3 a.out).
332 . Some formats leave the displacement part of an instruction
333 . empty (eg m88k bcs), this flag signals the fact.*}
334 . boolean pcrel_offset;
345 The HOWTO define is horrible and will go away.
348 .#define HOWTO(C, R,S,B, P, BI, ABS, O, SF, NAME, INPLACE, MASKSRC, MASKDST, PC) \
349 . {(unsigned)C,R,S,B, P, BI, ABS,O,SF,NAME,INPLACE,MASKSRC,MASKDST,PC}
352 And will be replaced with the totally magic way. But for the
353 moment, we are compatible, so do it this way..
356 .#define NEWHOWTO( FUNCTION, NAME,SIZE,REL,IN) HOWTO(0,0,SIZE,0,REL,0,false,false,FUNCTION, NAME,false,0,0,IN)
359 Helper routine to turn a symbol into a relocation value.
361 .#define HOWTO_PREPARE(relocation, symbol) \
363 . if (symbol != (asymbol *)NULL) { \
364 . if (symbol->section == &bfd_com_section) { \
368 . relocation = symbol->value; \
381 How relocs are tied together
383 .typedef unsigned char bfd_byte;
385 .typedef struct relent_chain {
387 . struct relent_chain *next;
396 bfd_perform_relocation
399 bfd_reloc_status_type
400 bfd_perform_relocation
402 arelent *reloc_entry,
404 asection *input_section,
408 If an output_bfd is supplied to this function the generated
409 image will be relocatable, the relocations are copied to the
410 output file after they have been changed to reflect the new
411 state of the world. There are two ways of reflecting the
412 results of partial linkage in an output file; by modifying the
413 output data in place, and by modifying the relocation record.
414 Some native formats (eg basic a.out and basic coff) have no
415 way of specifying an addend in the relocation type, so the
416 addend has to go in the output data. This is no big deal
417 since in these formats the output data slot will always be big
418 enough for the addend. Complex reloc types with addends were
419 invented to solve just this problem.
424 bfd_reloc_status_type
425 DEFUN(bfd_perform_relocation,(abfd,
431 arelent *reloc_entry AND
433 asection *input_section AND
437 bfd_reloc_status_type flag = bfd_reloc_ok;
438 bfd_vma addr = reloc_entry->address ;
439 bfd_vma output_base = 0;
440 reloc_howto_type *howto = reloc_entry->howto;
441 asection *reloc_target_output_section ;
445 symbol = *( reloc_entry->sym_ptr_ptr);
446 if ((symbol->section == &bfd_abs_section)
447 && output_bfd != (bfd *)NULL)
449 reloc_entry->address += input_section->output_offset;
455 if ((symbol->section == &bfd_und_section) && output_bfd == (bfd *)NULL) {
456 flag = bfd_reloc_undefined;
459 if (howto->special_function) {
460 bfd_reloc_status_type cont;
461 cont = howto->special_function(abfd,
467 if (cont != bfd_reloc_continue) return cont;
471 Work out which section the relocation is targetted at and the
472 initial relocation command value.
476 if (symbol->section == &bfd_com_section) {
480 relocation = symbol->value;
484 reloc_target_output_section = symbol->section->output_section;
486 if (output_bfd && howto->partial_inplace==false) {
490 output_base = reloc_target_output_section->vma;
494 relocation += output_base + symbol->section->output_offset;
497 relocation += reloc_entry->addend ;
500 if(reloc_entry->address > input_section->_cooked_size)
502 return bfd_reloc_outofrange;
506 if (howto->pc_relative == true)
509 Anything which started out as pc relative should end up that
512 There are two ways we can see a pcrel instruction. Sometimes
513 the pcrel displacement has been partially calculated, it
514 includes the distance from the start of the section to the
515 instruction in it (eg sun3), and sometimes the field is
516 totally blank - eg m88kbcs.
521 input_section->output_section->vma + input_section->output_offset;
523 if (howto->pcrel_offset == true) {
524 relocation -= reloc_entry->address;
529 if (output_bfd!= (bfd *)NULL)
531 if ( howto->partial_inplace == false)
534 This is a partial relocation, and we want to apply the relocation
535 to the reloc entry rather than the raw data. Modify the reloc
536 inplace to reflect what we now know.
538 reloc_entry->addend = relocation ;
539 reloc_entry->address += input_section->output_offset;
544 /* This is a partial relocation, but inplace, so modify the
547 If we've relocated with a symbol with a section, change
548 into a ref to the section belonging to the symbol
551 reloc_entry->address += input_section->output_offset;
553 if (abfd->xvec->flavour == bfd_target_coff_flavour)
555 relocation -= reloc_entry->addend;
556 reloc_entry->addend = 0;
560 reloc_entry->addend = relocation ;
566 reloc_entry->addend = 0;
571 Either we are relocating all the way, or we don't want to apply
572 the relocation to the reloc entry (probably because there isn't
573 any room in the output format to describe addends to relocs)
575 relocation >>= howto->rightshift;
577 /* Shift everything up to where it's going to be used */
579 relocation <<= howto->bitpos;
581 /* Wait for the day when all have the mask in them */
584 i instruction to be left alone
585 o offset within instruction
586 r relocation offset to apply
595 i i i i i o o o o o from bfd_get<size>
596 and S S S S S to get the size offset we want
597 + r r r r r r r r r r to get the final value to place
598 and D D D D D to chop to right size
599 -----------------------
602 ... i i i i i o o o o o from bfd_get<size>
603 and N N N N N get instruction
604 -----------------------
610 -----------------------
611 R R R R R R R R R R put into bfd_put<size>
615 x = ( (x & ~howto->dst_mask) | (((x & howto->src_mask) + relocation) & howto->dst_mask))
621 char x = bfd_get_8(abfd, (char *)data + addr);
623 bfd_put_8(abfd,x, (unsigned char *) data + addr);
629 short x = bfd_get_16(abfd, (bfd_byte *)data + addr);
631 bfd_put_16(abfd, x, (unsigned char *)data + addr);
636 long x = bfd_get_32(abfd, (bfd_byte *) data + addr);
638 bfd_put_32(abfd,x, (bfd_byte *)data + addr);
643 long x = bfd_get_32(abfd, (bfd_byte *) data + addr);
644 relocation = -relocation;
646 bfd_put_32(abfd,x, (bfd_byte *)data + addr);
655 return bfd_reloc_other;
666 howto manager, , typedef arelent, Relocations
671 When an application wants to create a relocation, but doesn't
672 know what the target machine might call it, it can find out by
673 using this bit of code.
682 The insides of a reloc code
686 .typedef enum bfd_reloc_code_real
689 . {* 16 bits wide, simple reloc *}
692 . {* 8 bits wide, but used to form an address like 0xffnn *}
695 . {* 8 bits wide, simple *}
698 . {* 8 bits wide, pc relative *}
701 . {* The type of reloc used to build a contructor table - at the
702 . moment probably a 32 bit wide abs address, but the cpu can
707 . {* 32 bits wide, simple reloc *}
709 . {* 32 bits, PC-relative *}
710 . BFD_RELOC_32_PCREL,
712 . {* High 22 bits of 32-bit value; simple reloc. *}
717 . {* Reloc types used for i960/b.out. *}
718 . BFD_RELOC_24_PCREL,
719 . BFD_RELOC_I960_CALLJ,
721 . BFD_RELOC_16_PCREL,
722 . {* 32-bit pc-relative, shifted right 2 bits (i.e., 30-bit
723 . word displacement, e.g. for SPARC) *}
724 . BFD_RELOC_32_PCREL_S2,
726 . {* now for the sparc/elf codes *}
727 . BFD_RELOC_NONE, {* actually used *}
728 . BFD_RELOC_SPARC_WDISP22,
731 . BFD_RELOC_SPARC_BASE13,
732 . BFD_RELOC_SPARC_GOT10,
733 . BFD_RELOC_SPARC_GOT13,
734 . BFD_RELOC_SPARC_GOT22,
735 . BFD_RELOC_SPARC_PC10,
736 . BFD_RELOC_SPARC_PC22,
737 . BFD_RELOC_SPARC_WPLT30,
738 . BFD_RELOC_SPARC_COPY,
739 . BFD_RELOC_SPARC_GLOB_DAT,
740 . BFD_RELOC_SPARC_JMP_SLOT,
741 . BFD_RELOC_SPARC_RELATIVE,
742 . BFD_RELOC_SPARC_UA32,
744 . {* this one is a.out specific? *}
745 . BFD_RELOC_SPARC_BASE22,
747 . {* this must be the highest numeric value *}
749 . } bfd_reloc_code_real_type;
756 bfd_reloc_type_lookup
759 CONST struct reloc_howto_struct *
760 bfd_reloc_type_lookup (bfd *abfd, bfd_reloc_code_real_type code);
763 This routine returns a pointer to a howto struct which when
764 invoked, will perform the supplied relocation on data from the
770 CONST struct reloc_howto_struct *
771 DEFUN(bfd_reloc_type_lookup,(abfd, code),
773 bfd_reloc_code_real_type code)
775 return BFD_SEND (abfd, reloc_type_lookup, (abfd, code));
778 static reloc_howto_type bfd_howto_32 =
779 HOWTO(0, 00,2,32,false,0,false,true,0,"VRT32", false,0xffffffff,0xffffffff,true);
784 bfd_default_reloc_type_lookup
787 CONST struct reloc_howto_struct *bfd_default_reloc_type_lookup
788 (CONST struct bfd_arch_info *,
789 bfd_reloc_code_real_type code);
792 Provides a default relocation lookuperer for any architectue
796 CONST struct reloc_howto_struct *
797 DEFUN(bfd_default_reloc_type_lookup,(arch, code),
798 CONST struct bfd_arch_info *arch AND
799 bfd_reloc_code_real_type code)
804 /* The type of reloc used in a ctor, which will be as wide as the
805 address - so either a 64, 32, or 16 bitter.. */
806 switch (arch->bits_per_address) {
810 return &bfd_howto_32;
819 return (CONST struct reloc_howto_struct *)NULL;
825 bfd_generic_relax_section
828 boolean bfd_generic_relax_section
834 Provides default handling for relaxing for back ends which
835 don't do relaxing -- i.e., does nothing.
839 DEFUN(bfd_generic_relax_section,(abfd, section, symbols),
841 asection *section AND
852 bfd_generic_get_relocated_section_contents
856 bfd_generic_get_relocated_section_contents(bfd *abfd,
857 struct bfd_seclet_struct *seclet,
861 Provides default handling of relocation effort for back ends
862 which can't be bothered to do it efficiently.
867 DEFUN(bfd_generic_get_relocated_section_contents,(abfd, seclet, data),
869 struct bfd_seclet_struct *seclet AND
872 extern bfd_error_vector_type bfd_error_vector;
874 /* Get enough memory to hold the stuff */
875 bfd *input_bfd = seclet->u.indirect.section->owner;
876 asection *input_section = seclet->u.indirect.section;
880 bfd_size_type reloc_size = bfd_get_reloc_upper_bound(input_bfd,
882 arelent **reloc_vector = (arelent **) alloca(reloc_size);
884 /* read in the section */
885 bfd_get_section_contents(input_bfd,
889 input_section->_raw_size);
891 /* We're not relaxing the section, so just copy the size info */
892 input_section->_cooked_size = input_section->_raw_size;
893 input_section->reloc_done = true;
896 if (bfd_canonicalize_reloc(input_bfd,
899 seclet->u.indirect.symbols) )
902 for (parent = reloc_vector; * parent != (arelent *)NULL;
905 bfd_reloc_status_type r=
906 bfd_perform_relocation(input_bfd,
912 if (r != bfd_reloc_ok)
916 case bfd_reloc_undefined:
917 bfd_error_vector.undefined_symbol(*parent, seclet);
919 case bfd_reloc_dangerous:
920 bfd_error_vector.reloc_dangerous(*parent, seclet);
922 case bfd_reloc_outofrange:
923 case bfd_reloc_overflow:
924 bfd_error_vector.reloc_value_truncated(*parent, seclet);