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,
299 . bfd *output_bfd ));
301 . {* The textual name of the relocation type. *}
304 . {* When performing a partial link, some formats must modify the
305 . relocations rather than the data - this flag signals this.*}
306 . boolean partial_inplace;
308 . {* The src_mask is used to select what parts of the read in data
309 . are to be used in the relocation sum. Eg, if this was an 8 bit
310 . bit of data which we read and relocated, this would be
311 . 0x000000ff. When we have relocs which have an addend, such as
312 . sun4 extended relocs, the value in the offset part of a
313 . relocating field is garbage so we never use it. In this case
314 . the mask would be 0x00000000. *}
317 . {* The dst_mask is what parts of the instruction are replaced
318 . into the instruction. In most cases src_mask == dst_mask,
319 . except in the above special case, where dst_mask would be
320 . 0x000000ff, and src_mask would be 0x00000000. *}
323 . {* When some formats create PC relative instructions, they leave
324 . the value of the pc of the place being relocated in the offset
325 . slot of the instruction, so that a PC relative relocation can
326 . be made just by adding in an ordinary offset (eg sun3 a.out).
327 . Some formats leave the displacement part of an instruction
328 . empty (eg m88k bcs), this flag signals the fact.*}
329 . boolean pcrel_offset;
340 The HOWTO define is horrible and will go away.
343 .#define HOWTO(C, R,S,B, P, BI, ABS, O, SF, NAME, INPLACE, MASKSRC, MASKDST, PC) \
344 . {(unsigned)C,R,S,B, P, BI, ABS,O,SF,NAME,INPLACE,MASKSRC,MASKDST,PC}
347 And will be replaced with the totally magic way. But for the
348 moment, we are compatible, so do it this way..
351 .#define NEWHOWTO( FUNCTION, NAME,SIZE,REL,IN) HOWTO(0,0,SIZE,0,REL,0,false,false,FUNCTION, NAME,false,0,0,IN)
354 Helper routine to turn a symbol into a relocation value.
356 .#define HOWTO_PREPARE(relocation, symbol) \
358 . if (symbol != (asymbol *)NULL) { \
359 . if (symbol->section == &bfd_com_section) { \
363 . relocation = symbol->value; \
376 How relocs are tied together
378 .typedef unsigned char bfd_byte;
380 .typedef struct relent_chain {
382 . struct relent_chain *next;
391 bfd_perform_relocation
394 bfd_reloc_status_type
395 bfd_perform_relocation
397 arelent *reloc_entry,
399 asection *input_section,
403 If an output_bfd is supplied to this function the generated
404 image will be relocatable, the relocations are copied to the
405 output file after they have been changed to reflect the new
406 state of the world. There are two ways of reflecting the
407 results of partial linkage in an output file; by modifying the
408 output data in place, and by modifying the relocation record.
409 Some native formats (eg basic a.out and basic coff) have no
410 way of specifying an addend in the relocation type, so the
411 addend has to go in the output data. This is no big deal
412 since in these formats the output data slot will always be big
413 enough for the addend. Complex reloc types with addends were
414 invented to solve just this problem.
419 bfd_reloc_status_type
420 DEFUN(bfd_perform_relocation
,(abfd
,
426 arelent
*reloc_entry AND
428 asection
*input_section AND
432 bfd_reloc_status_type flag
= bfd_reloc_ok
;
433 bfd_vma addr
= reloc_entry
->address
;
434 bfd_vma output_base
= 0;
435 reloc_howto_type
*howto
= reloc_entry
->howto
;
436 asection
*reloc_target_output_section
;
440 symbol
= *( reloc_entry
->sym_ptr_ptr
);
441 if ((symbol
->section
== &bfd_abs_section
)
442 && output_bfd
!= (bfd
*)NULL
)
444 reloc_entry
->address
+= input_section
->output_offset
;
450 if ((symbol
->section
== &bfd_und_section
) && output_bfd
== (bfd
*)NULL
) {
451 flag
= bfd_reloc_undefined
;
454 if (howto
->special_function
) {
455 bfd_reloc_status_type cont
;
456 cont
= howto
->special_function(abfd
,
462 if (cont
!= bfd_reloc_continue
) return cont
;
466 Work out which section the relocation is targetted at and the
467 initial relocation command value.
471 if (symbol
->section
== &bfd_com_section
) {
475 relocation
= symbol
->value
;
479 reloc_target_output_section
= symbol
->section
->output_section
;
481 if (output_bfd
&& howto
->partial_inplace
==false) {
485 output_base
= reloc_target_output_section
->vma
;
489 relocation
+= output_base
+ symbol
->section
->output_offset
;
492 relocation
+= reloc_entry
->addend
;
495 if(reloc_entry
->address
> input_section
->_cooked_size
)
497 return bfd_reloc_outofrange
;
501 if (howto
->pc_relative
== true)
504 Anything which started out as pc relative should end up that
507 There are two ways we can see a pcrel instruction. Sometimes
508 the pcrel displacement has been partially calculated, it
509 includes the distance from the start of the section to the
510 instruction in it (eg sun3), and sometimes the field is
511 totally blank - eg m88kbcs.
516 input_section
->output_section
->vma
+ input_section
->output_offset
;
518 if (howto
->pcrel_offset
== true) {
519 relocation
-= reloc_entry
->address
;
524 if (output_bfd
!= (bfd
*)NULL
) {
525 if ( howto
->partial_inplace
== false) {
527 This is a partial relocation, and we want to apply the relocation
528 to the reloc entry rather than the raw data. Modify the reloc
529 inplace to reflect what we now know.
531 reloc_entry
->addend
= relocation
;
532 reloc_entry
->address
+= input_section
->output_offset
;
537 /* This is a partial relocation, but inplace, so modify the
540 If we've relocated with a symbol with a section, change
541 into a ref to the section belonging to the symbol
543 reloc_entry
->addend
= relocation
;
544 reloc_entry
->address
+= input_section
->output_offset
;
552 reloc_entry
->addend
= 0;
558 Either we are relocating all the way, or we don't want to apply
559 the relocation to the reloc entry (probably because there isn't
560 any room in the output format to describe addends to relocs)
562 relocation
>>= howto
->rightshift
;
564 /* Shift everything up to where it's going to be used */
566 relocation
<<= howto
->bitpos
;
568 /* Wait for the day when all have the mask in them */
571 i instruction to be left alone
572 o offset within instruction
573 r relocation offset to apply
582 i i i i i o o o o o from bfd_get<size>
583 and S S S S S to get the size offset we want
584 + r r r r r r r r r r to get the final value to place
585 and D D D D D to chop to right size
586 -----------------------
589 ... i i i i i o o o o o from bfd_get<size>
590 and N N N N N get instruction
591 -----------------------
597 -----------------------
598 R R R R R R R R R R put into bfd_put<size>
602 x = ( (x & ~howto->dst_mask) | (((x & howto->src_mask) + relocation) & howto->dst_mask))
608 char x
= bfd_get_8(abfd
, (char *)data
+ addr
);
610 bfd_put_8(abfd
,x
, (unsigned char *) data
+ addr
);
616 short x
= bfd_get_16(abfd
, (bfd_byte
*)data
+ addr
);
618 bfd_put_16(abfd
, x
, (unsigned char *)data
+ addr
);
623 long x
= bfd_get_32(abfd
, (bfd_byte
*) data
+ addr
);
625 bfd_put_32(abfd
,x
, (bfd_byte
*)data
+ addr
);
633 return bfd_reloc_other
;
643 howto manager, , typedef arelent, Relocations
648 When an application wants to create a relocation, but doesn't
649 know what the target machine might call it, it can find out by
650 using this bit of code.
659 The insides of a reloc code
663 .typedef enum bfd_reloc_code_real
665 . {* 16 bits wide, simple reloc *}
668 . {* 8 bits wide, but used to form an address like 0xffnn *}
671 . {* 8 bits wide, simple *}
674 . {* 8 bits wide, pc relative *}
677 . {* The type of reloc used to build a contructor table - at the
678 . moment probably a 32 bit wide abs address, but the cpu can
683 . {* 32 bits wide, simple reloc *}
685 . {* 32 bits, PC-relative *}
686 . BFD_RELOC_32_PCREL,
688 . {* High 22 bits of 32-bit value; simple reloc. *}
693 . {* Reloc types used for i960/b.out. *}
694 . BFD_RELOC_24_PCREL,
695 . BFD_RELOC_I960_CALLJ,
697 . BFD_RELOC_16_PCREL,
698 . {* 32-bit pc-relative, shifted right 2 bits (i.e., 30-bit
699 . word displacement, e.g. for SPARC) *}
700 . BFD_RELOC_32_PCREL_S2,
702 . {* now for the sparc/elf codes *}
703 . BFD_RELOC_NONE, {* actually used *}
704 . BFD_RELOC_SPARC_WDISP22,
707 . BFD_RELOC_SPARC_BASE13,
708 . BFD_RELOC_SPARC_GOT10,
709 . BFD_RELOC_SPARC_GOT13,
710 . BFD_RELOC_SPARC_GOT22,
711 . BFD_RELOC_SPARC_PC10,
712 . BFD_RELOC_SPARC_PC22,
713 . BFD_RELOC_SPARC_WPLT30,
714 . BFD_RELOC_SPARC_COPY,
715 . BFD_RELOC_SPARC_GLOB_DAT,
716 . BFD_RELOC_SPARC_JMP_SLOT,
717 . BFD_RELOC_SPARC_RELATIVE,
718 . BFD_RELOC_SPARC_UA32,
720 . {* this one is a.out specific? *}
721 . BFD_RELOC_SPARC_BASE22,
723 . {* this must be the highest numeric value *}
725 . } bfd_reloc_code_real_type;
732 bfd_reloc_type_lookup
735 CONST struct reloc_howto_struct *
736 bfd_reloc_type_lookup (bfd *abfd, bfd_reloc_code_real_type code);
739 This routine returns a pointer to a howto struct which when
740 invoked, will perform the supplied relocation on data from the
746 CONST
struct reloc_howto_struct
*
747 DEFUN(bfd_reloc_type_lookup
,(abfd
, code
),
749 bfd_reloc_code_real_type code
)
751 return BFD_SEND (abfd
, reloc_type_lookup
, (abfd
, code
));
754 static reloc_howto_type bfd_howto_32
=
755 HOWTO(0, 00,2,32,false,0,false,true,0,"VRT32", false,0xffffffff,0xffffffff,true);
760 bfd_default_reloc_type_lookup
763 CONST struct reloc_howto_struct *bfd_default_reloc_type_lookup
764 (CONST struct bfd_arch_info *,
765 bfd_reloc_code_real_type code);
768 Provides a default relocation lookuperer for any architectue
772 CONST
struct reloc_howto_struct
*
773 DEFUN(bfd_default_reloc_type_lookup
,(arch
, code
),
774 CONST
struct bfd_arch_info
*arch AND
775 bfd_reloc_code_real_type code
)
780 /* The type of reloc used in a ctor, which will be as wide as the
781 address - so either a 64, 32, or 16 bitter.. */
782 switch (arch
->bits_per_address
) {
786 return &bfd_howto_32
;
795 return (struct reloc_howto_struct
*)NULL
;
801 bfd_generic_relax_section
804 boolean bfd_generic_relax_section
810 Provides default handling for relaxing for back ends which
811 don't do relaxing -- i.e., does nothing.
815 DEFUN(bfd_generic_relax_section
,(abfd
, section
, symbols
),
817 asection
*section AND
828 bfd_generic_get_relocated_section_contents
832 bfd_generic_get_relocated_section_contents(bfd *abfd,
833 struct bfd_seclet_struct *seclet,
837 Provides default handling of relocation effort for back ends
838 which can't be bothered to do it efficiently.
843 DEFUN(bfd_generic_get_relocated_section_contents
,(abfd
, seclet
, data
),
845 struct bfd_seclet_struct
*seclet AND
848 extern bfd_error_vector_type bfd_error_vector
;
850 /* Get enough memory to hold the stuff */
851 bfd
*input_bfd
= seclet
->u
.indirect
.section
->owner
;
852 asection
*input_section
= seclet
->u
.indirect
.section
;
856 bfd_size_type reloc_size
= bfd_get_reloc_upper_bound(input_bfd
,
858 arelent
**reloc_vector
= (arelent
**) alloca(reloc_size
);
860 /* read in the section */
861 bfd_get_section_contents(input_bfd
,
865 input_section
->_raw_size
);
867 /* We're not relaxing the section, so just copy the size info */
868 input_section
->_cooked_size
= input_section
->_raw_size
;
869 input_section
->reloc_done
= true;
872 if (bfd_canonicalize_reloc(input_bfd
,
875 seclet
->u
.indirect
.symbols
) )
878 for (parent
= reloc_vector
; * parent
!= (arelent
*)NULL
;
881 bfd_reloc_status_type r
=
882 bfd_perform_relocation(input_bfd
,
888 if (r
!= bfd_reloc_ok
)
892 case bfd_reloc_undefined
:
893 bfd_error_vector
.undefined_symbol(*parent
, seclet
);
895 case bfd_reloc_dangerous
:
896 bfd_error_vector
.reloc_dangerous(*parent
, seclet
);
898 case bfd_reloc_outofrange
:
899 case bfd_reloc_overflow
:
900 bfd_error_vector
.reloc_value_truncated(*parent
, seclet
);