4 #include <libelfu/libelfu.h>
7 static void* subFindByName(ElfuElf *me, ElfuScn *ms, void *aux1, void *aux2)
9 char *name = (char*)aux1;
12 if (elfu_mScnName(me, ms)) {
13 if (!strcmp(elfu_mScnName(me, ms), name)) {
22 /* Hazard a guess where a function may be found in the PLT */
23 static GElf_Word pltLookupVal(ElfuElf *metarget, char *name)
30 relplt = elfu_mScnForall(metarget, subFindByName, ".rel.plt", NULL);
32 ELFU_WARN("dynsymLookupVal: Could not find .rel.plt section in destination ELF.\n");
36 plt = elfu_mScnForall(metarget, subFindByName, ".plt", NULL);
38 ELFU_WARN("dynsymLookupVal: Could not find .plt section in destination ELF.\n");
43 /* Look up name. If the j-th entry in .rel.plt has the name we are
44 * looking for, we assume that the (j+1)-th entry in .plt is machine
45 * code to jump to the function.
46 * Your mileage may vary, but it works on my GNU binaries. */
47 assert(relplt->linkptr);
49 CIRCLEQ_FOREACH(rel, &relplt->reltab.rels, elem) {
56 /* We only consider runtime relocations for functions.
57 * Technically, these relocations write the functions' addresses
58 * to the GOT, not the PLT, after the dynamic linker has found
60 if (rel->type != R_386_JMP_SLOT) {
64 /* Get the (rel->sym)-th symbol from the symbol table that
65 * .rel.plt points to. */
66 sym = CIRCLEQ_FIRST(&relplt->linkptr->symtab.syms);
67 for (i = 1; i < rel->sym; i++) {
68 sym = CIRCLEQ_NEXT(sym, elem);
71 symname = ELFU_SYMSTR(relplt->linkptr, sym->name);
72 if (!strcmp(symname, name)) {
73 /* If this is the symbol we are looking for, then in an x86 binary
74 * the jump to the dynamic symbol is probably at offset (j * 16)
75 * from the start of the PLT, where j is the PLT entry and 16 is
76 * the number of bytes the machine code in a PLT entry take. */
77 GElf_Addr addr = plt->shdr.sh_addr + (16 * j);
78 ELFU_DEBUG("dynsymLookupVal: Guessing symbol '%s' is in destination memory at %jx (PLT entry #%d).\n", name, addr, j);
83 ELFU_WARN("dynsymLookupVal: Could not find symbol '%s' in destination ELF.\n", name);
89 static GElf_Word symtabLookupVal(ElfuElf *metarget, ElfuScn *msst, GElf_Word entry)
98 assert(!CIRCLEQ_EMPTY(&msst->symtab.syms));
100 sym = CIRCLEQ_FIRST(&msst->symtab.syms);
101 for (i = 1; i < entry; i++) {
102 sym = CIRCLEQ_NEXT(sym, elem);
104 symname = ELFU_SYMSTR(msst, sym->name);
111 ElfuScn *newscn = elfu_mScnByOldscn(metarget, sym->scnptr);
113 return newscn->shdr.sh_addr + sym->value;
114 } else if (sym->shndx == SHN_UNDEF) {
115 /* Look the symbol up in .rel.plt. If it cannot be found there then
116 * .rel.dyn may need to be expanded with a COPY relocation so the
117 * dynamic linker fixes up the (TODO). */
118 return pltLookupVal(metarget, symname);
119 } else if (sym->shndx == SHN_ABS) {
122 ELFU_WARN("symtabLookupVal: Symbol binding COMMON is not supported, using 0.\n");
128 assert(elfu_mScnByOldscn(metarget, sym->scnptr));
129 return elfu_mScnByOldscn(metarget, sym->scnptr)->shdr.sh_addr;
131 ELFU_WARN("symtabLookupVal: Symbol type FILE is not supported, using 0.\n");
134 ELFU_WARN("symtabLookupVal: Unknown symbol type %d for %s.\n", sym->type, symname);
139 void elfu_mRelocate32(ElfuElf *metarget, ElfuScn *mstarget, ElfuScn *msrt)
146 ELFU_DEBUG("Relocating in section of type %d size %jx\n",
147 mstarget->shdr.sh_type,
148 mstarget->shdr.sh_size);
150 CIRCLEQ_FOREACH(rel, &msrt->reltab.rels, elem) {
151 Elf32_Word *dest = (Elf32_Word*)(((char*)(mstarget->data.d_buf)) + rel->offset);
152 Elf32_Word a = rel->addendUsed ? rel->addend : *dest;
153 Elf32_Addr p = mstarget->shdr.sh_addr + rel->offset;
154 Elf32_Addr s = symtabLookupVal(metarget, msrt->linkptr, rel->sym);
155 Elf32_Word newval = *dest;
159 ELFU_DEBUG("Skipping relocation: R_386_NONE");
162 ELFU_DEBUG("Relocation: R_386_32");
166 ELFU_DEBUG("Relocation: R_386_PC32");
171 ELFU_DEBUG("Skipping relocation: Unknown type %d", rel->type);
173 ELFU_DEBUG(", overwriting %x with %x.\n", *dest, newval);