Consolidate all relocations in relocate_section

Static relocation of functions in dynamic libraries must use the PLT entry as the target. Before this commit, it used to be done in 2 parts for ARM, with the offset of the PLT entry from the beginning of the PLT being put in the relocated place in build_got_entries () and then the address of the PLT being added in relocate_section. This led to code dealing with reading the offset of a bl instruction in build_got_entries. Furthermore, the addition of the address of the start of the PLT was done based on the relocation type which does not convey whether a PLT entry should be used to reach the symbol. This commit moves the decision to use the PLT as the target in relocate_section, therefore having the instruction aware code contained to the target-specific bit of that function (in <target>-link.c). Note that relocate_syms is *not* the right place to do this because two different relocations for the same symbol can make different decision. This is the case in tcc -run mode where the static and dynamic relocation are done by tcc. Storing the PLT entry address in the symbol's st_value field and relying on the specific relocation type being used for dynamic relocation would work but the PLT entry address would then appear in the static symbol table (symtab). This would also make the static symbol table entry differ from the dynamic symbol table entry.

Thomas Preud'homme committed 10 years ago

Commit 25927df1 parent 2c388004 files · +22 −66Browse files

Unified · Split

4 files

arm-link.c +0 −4
arm64-link.c +0 −8
tccelf.c +21 −49
x86_64-link.c +1 −5

arm-link.c+0−4

@@ -43,8 +43,6 @@ void relocate(TCCState s1, ElfW_Rel rel, int type, char *ptr, addr_t addr, add · 42 unmodified lines
43	43	{
44	44	int x, is_thumb, is_call, h, blx_avail, is_bl, th_ko;
45	45	x = ((int ) ptr) & 0xffffff;
46		− if (sym->st_shndx == SHN_UNDEF \|\| sym->st_shndx == SHN_ABS)
47		− val = s1->plt->sh_addr;
48	46	#ifdef DEBUG_RELOC
49	47	printf ("reloc %d: x=0x%x val=0x%x ", type, x, val);
50	48	#endif
@@ -140,8 +138,6 @@ void relocate(TCCState s1, ElfW_Rel rel, int type, char *ptr, addr_t addr, add · 89 unmodified lines
140	138	}
141	139
142	140	/* Compute final offset */
143		− if (to_plt && !is_call) /* Point to 1st instr of Thumb stub */
144		− x -= 4;
145	141	x += val - addr;
146	142	if (!to_thumb && is_call) {
147	143	blx_bit = 0; /* bl -> blx */

arm64-link.c+0−8

@@ -65,14 +65,6 @@ void relocate(TCCState s1, ElfW_Rel rel, int type, char *ptr, addr_t addr, add · 64 unmodified lines
65	65	return;
66	66	case R_AARCH64_JUMP26:
67	67	case R_AARCH64_CALL26:
68		− /* This check must match the one in build_got_entries, testing
69		− if we really need a PLT slot. */
70		− if (sym->st_shndx == SHN_UNDEF \|\|
71		− sym->st_shndx == SHN_ABS)
72		− /* We've put the PLT slot offset into r_addend when generating
73		− it, and that's what we must use as relocation value (adjusted
74		− by section offset of course). */
75		− val = s1->plt->sh_addr + rel->r_addend;
76	68	#ifdef DEBUG_RELOC
77	69	printf ("reloc %d @ 0x%lx: val=0x%lx name=%s\n", type, addr, val,
78	70	(char *) symtab_section->link->data + sym->st_name);

tccelf.c+21−49

@@ -654,8 +654,8 @@ ST_FUNC void relocate_common_syms(void) · 653 unmodified lines
654	654	true and output error if undefined symbol. */
655	655	ST_FUNC void relocate_syms(TCCState *s1, int do_resolve)
656	656	{
657		− ElfW(Sym) sym, esym;
658		− int sym_bind, sh_num, sym_index;
	657	+ ElfW(Sym) *sym;
	658	+ int sym_bind, sh_num;
659	659	const char *name;
660	660
661	661	for_each_elem(symtab_section, 1, sym, ElfW(Sym)) {
@@ -676,15 +676,9 @@ ST_FUNC void relocate_syms(TCCState *s1, int do_resolve) · 14 unmodified lines
676	676	goto found;
677	677	}
678	678	#endif
679		− } else if (s1->dynsym) {
680		− /* if dynamic symbol exist, then use it */
681		− sym_index = find_elf_sym(s1->dynsym, name);
682		− if (sym_index) {
683		− esym = &((ElfW(Sym) *)s1->dynsym->data)[sym_index];
684		− sym->st_value = esym->st_value;
685		− goto found;
686		− }
687		− }
	679	+ /* if dynamic symbol exist, it will be used in relocate_section */
	680	+ } else if (s1->dynsym && find_elf_sym(s1->dynsym, name))
	681	+ goto found;
688	682	/* XXX: _fp_hw seems to be part of the ABI, so we ignore
689	683	it */
690	684	if (!strcmp(name, "_fp_hw"))
@@ -714,7 +708,8 @@ ST_FUNC void relocate_section(TCCState s1, Section s) · 23 unmodified lines
714	708	ElfW(Sym) *sym;
715	709	int type, sym_index;
716	710	unsigned char *ptr;
717		− addr_t val, addr;
	711	+ addr_t tgt, addr;
	712	+ struct sym_attr *symattr;
718	713
719	714	relocate_init(sr);
720	715	for_each_elem(sr, 0, rel, ElfW_Rel) {
@@ -722,14 +717,22 @@ ST_FUNC void relocate_section(TCCState s1, Section s) · 1 unmodified line
722	717
723	718	sym_index = ELFW(R_SYM)(rel->r_info);
724	719	sym = &((ElfW(Sym) *)symtab_section->data)[sym_index];
725		− val = sym->st_value;
	720	+ type = ELFW(R_TYPE)(rel->r_info);
	721	+ symattr = get_sym_attr(s1, sym_index, 0);
	722	+ tgt = sym->st_value;
	723	+ /* If static relocation to a dynamic symbol, relocate to PLT entry.
	724	+ Note 1: in tcc -run mode we go through PLT to avoid range issues
	725	+ Note 2: symbols compiled with libtcc and later added with
	726	+ tcc_add_symbol are not dynamic and thus have symattr NULL */
	727	+ if (relocs_info[type].gotplt_entry != NO_GOTPLT_ENTRY &&
	728	+ relocs_info[type].code_reloc && symattr && symattr->plt_offset)
	729	+ tgt = s1->plt->sh_addr + symattr->plt_offset;
726	730	#if defined(TCC_TARGET_ARM64) \|\| defined(TCC_TARGET_X86_64)
727		− val += rel->r_addend;
	731	+ tgt += rel->r_addend;
728	732	#endif
729		− type = ELFW(R_TYPE)(rel->r_info);
730	733	addr = s->sh_addr + rel->r_offset;
731	734
732		− relocate(s1, rel, type, ptr, addr, val);
	735	+ relocate(s1, rel, type, ptr, addr, tgt);
733	736	}
734	737	/* if the relocation is allocated, we change its symbol table */
735	738	if (sr->sh_flags & SHF_ALLOC)
@@ -1030,7 +1033,6 @@ ST_FUNC void build_got_entries(TCCState *s1) · 294 unmodified lines
1030	1033	ElfW_Rel *rel;
1031	1034	ElfW(Sym) *sym;
1032	1035	int i, type, reloc_type, sym_index;
1033		− unsigned long ofs;
1034	1036
1035	1037	for(i = 1; i < s1->nb_sections; i++) {
1036	1038	s = s1->sections[i];
@@ -1075,38 +1077,8 @@ ST_FUNC void build_got_entries(TCCState *s1) · 38 unmodified lines
1075	1077	reloc_type = R_JMP_SLOT;
1076	1078	else
1077	1079	reloc_type = R_GLOB_DAT;
1078		− ofs = put_got_entry(s1, reloc_type, type, sym->st_size,
1079		− sym->st_info, sym_index);
1080		−
1081		−#ifdef DEBUG_RELOC
1082		− printf ("maybegot: %s, %d, %d --> ofs=0x%x\n",
1083		− (char *) symtab_section->link->data + sym->st_name, type,
1084		− sym->st_shndx, ofs);
1085		−#endif
1086		−
1087		−#if defined (TCC_TARGET_X86_64) \|\| defined(TCC_TARGET_ARM64)
1088		− /* We store the place of the generated PLT slot in our addend. */
1089		− if (relocs_info[type].pltoff_addend)
1090		− rel->r_addend += ofs;
1091		−
1092		−#elif defined (TCC_TARGET_ARM)
1093		− if (type == R_ARM_PC24 \|\| type == R_ARM_CALL \|\|
1094		− type == R_ARM_JUMP24 \|\| type == R_ARM_PLT32) {
1095		− addr_t ptr = (addr_t)(s1->sections[s->sh_info]->data
1096		− + rel->r_offset);
1097		− /* x must be signed! */
1098		− int x = *ptr & 0xffffff;
1099		− x = (x << 8) >> 8;
1100		− x <<= 2;
1101		− x += ofs;
1102		− x >>= 2;
1103		−#ifdef DEBUG_RELOC
1104		− printf ("insn=0x%x --> 0x%x (x==0x%x)\n", *ptr,
1105		− (*ptr & 0xff000000) \| x, x);
1106		−#endif
1107		− ptr = (ptr & 0xff000000) \| x;
1108		− }
1109		−#endif
	1080	+ put_got_entry(s1, reloc_type, type, sym->st_size, sym->st_info,
	1081	+ sym_index);
1110	1082	}
1111	1083	}
1112	1084	}

x86_64-link.c+1−5

@@ -75,11 +75,7 @@ void relocate(TCCState s1, ElfW_Rel rel, int type, char *ptr, addr_t addr, add · 74 unmodified lines
75	75	goto plt32pc32;
76	76
77	77	case R_X86_64_PLT32:
78		− /* We've put the PLT slot offset into r_addend when generating
79		− it, and that's what we must use as relocation value (adjusted
80		− by section offset of course). */
81		− val = s1->plt->sh_addr + rel->r_addend;
82		− /* fallthrough. */
	78	+ /* fallthrough: val already holds the PLT slot address */
83	79
84	80	plt32pc32:
85	81	{

Consolidate all relocations in relocate_section

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