summaryrefslogtreecommitdiff
path: root/src/modelops/symtab.c
diff options
context:
space:
mode:
Diffstat (limited to 'src/modelops/symtab.c')
-rw-r--r--src/modelops/symtab.c223
1 files changed, 223 insertions, 0 deletions
diff --git a/src/modelops/symtab.c b/src/modelops/symtab.c
new file mode 100644
index 0000000..a7c1485
--- /dev/null
+++ b/src/modelops/symtab.c
@@ -0,0 +1,223 @@
+#include <assert.h>
+#include <stdlib.h>
+#include <string.h>
+#include <libelfu/libelfu.h>
+
+
+static void* subFindByName(ElfuElf *me, ElfuScn *ms, void *aux1, void *aux2)
+{
+ char *name = (char*)aux1;
+ (void)aux2;
+
+ if (elfu_mScnName(me, ms)) {
+ if (!strcmp(elfu_mScnName(me, ms), name)) {
+ return ms;
+ }
+ }
+
+ /* Continue */
+ return NULL;
+}
+
+/* Hazard a guess where a function may be found in the PLT */
+static GElf_Word pltLookupVal(ElfuElf *me, char *name)
+{
+ ElfuScn *relplt;
+ ElfuScn *plt;
+ ElfuRel *rel;
+ GElf_Word j;
+
+ relplt = elfu_mScnForall(me, subFindByName, ".rel.plt", NULL);
+ if (!relplt) {
+ ELFU_WARN("dynsymLookupVal: Could not find .rel.plt section in destination ELF.\n");
+ return 0;
+ }
+
+ plt = elfu_mScnForall(me, subFindByName, ".plt", NULL);
+ if (!plt) {
+ ELFU_WARN("dynsymLookupVal: Could not find .plt section in destination ELF.\n");
+ return 0;
+ }
+
+
+ /* Look up name. If the j-th entry in .rel.plt has the name we are
+ * looking for, we assume that the (j+1)-th entry in .plt is machine
+ * code to jump to the function.
+ * Your mileage may vary, but it works on my GNU binaries. */
+ assert(relplt->linkptr);
+ j = 0;
+ CIRCLEQ_FOREACH(rel, &relplt->reltab.rels, elem) {
+ GElf_Word i;
+ ElfuSym *sym;
+ char *symname;
+
+ j++;
+
+ /* We only consider runtime relocations for functions.
+ * Technically, these relocations write the functions' addresses
+ * to the GOT, not the PLT, after the dynamic linker has found
+ * them. */
+ if ((me->elfclass == ELFCLASS32 && rel->type != R_386_JMP_SLOT)
+ || (me->elfclass == ELFCLASS64 && rel->type != R_X86_64_JUMP_SLOT)) {
+ continue;
+ }
+
+ /* Get the (rel->sym)-th symbol from the symbol table that
+ * .rel.plt points to. */
+ sym = CIRCLEQ_FIRST(&relplt->linkptr->symtab.syms);
+ for (i = 1; i < rel->sym; i++) {
+ sym = CIRCLEQ_NEXT(sym, elem);
+ }
+
+ symname = ELFU_SYMSTR(relplt->linkptr, sym->name);
+ if (!strcmp(symname, name)) {
+ /* If this is the symbol we are looking for, then in an x86 binary
+ * the jump to the dynamic symbol is probably at offset (j * 16)
+ * from the start of the PLT, where j is the PLT entry and 16 is
+ * the number of bytes the machine code in a PLT entry take. */
+ GElf_Addr addr = plt->shdr.sh_addr + (16 * j);
+ ELFU_DEBUG("dynsymLookupVal: Guessing symbol '%s' is in destination memory at %jx (PLT entry #%d).\n", name, addr, j);
+ return addr;
+ }
+ }
+
+ ELFU_WARN("dynsymLookupVal: Could not find symbol '%s' in destination ELF.\n", name);
+
+ return 0;
+}
+
+
+
+/* Look up a value in the symbol table section *msst which is in *me.
+ * If it is not found there, see if we can find it in *me's PLT. */
+GElf_Word elfu_mSymtabLookupVal(ElfuElf *me, ElfuScn *msst, GElf_Word entry)
+{
+ GElf_Word i;
+ ElfuSym *sym;
+ char *symname;
+
+ assert(me);
+ assert(msst);
+ assert(entry > 0);
+ assert(!CIRCLEQ_EMPTY(&msst->symtab.syms));
+
+ sym = CIRCLEQ_FIRST(&msst->symtab.syms);
+ for (i = 1; i < entry; i++) {
+ sym = CIRCLEQ_NEXT(sym, elem);
+ }
+ symname = ELFU_SYMSTR(msst, sym->name);
+
+ switch (sym->type) {
+ case STT_NOTYPE:
+ case STT_OBJECT:
+ case STT_FUNC:
+ if (sym->scnptr) {
+ ElfuScn *newscn = elfu_mScnByOldscn(me, sym->scnptr);
+ assert(newscn);
+ return newscn->shdr.sh_addr + sym->value;
+ } else if (sym->shndx == SHN_UNDEF) {
+ /* Look the symbol up in .rel.plt. If it cannot be found there then
+ * .rel.dyn may need to be expanded with a COPY relocation so the
+ * dynamic linker fixes up the (TODO). */
+ return pltLookupVal(me, symname);
+ } else if (sym->shndx == SHN_ABS) {
+ return sym->value;
+ } else {
+ ELFU_WARN("symtabLookupVal: Symbol binding COMMON is not supported, using 0.\n");
+ return 0;
+ }
+ break;
+ case STT_SECTION:
+ assert(sym->scnptr);
+ assert(elfu_mScnByOldscn(me, sym->scnptr));
+ return elfu_mScnByOldscn(me, sym->scnptr)->shdr.sh_addr;
+ case STT_FILE:
+ ELFU_WARN("symtabLookupVal: Symbol type FILE is not supported, using 0.\n");
+ return 0;
+ default:
+ ELFU_WARN("symtabLookupVal: Unknown symbol type %d for %s.\n", sym->type, symname);
+ return 0;
+ }
+}
+
+
+
+/* Convert symtab from memory model to elfclass specific format */
+void elfu_mSymtabFlatten(ElfuElf *me)
+{
+ ElfuSym *sym;
+ size_t numsyms = 0;
+
+ elfu_mLayoutAuto(me);
+
+ /* Update section indexes and count symbols */
+ CIRCLEQ_FOREACH(sym, &me->symtab->symtab.syms, elem) {
+ if (sym->scnptr) {
+ sym->shndx = elfu_mScnIndex(me, sym->scnptr);
+ }
+
+ numsyms++;
+ }
+
+ /* Copy symbols to elfclass-specific format */
+ if (me->elfclass == ELFCLASS32) {
+ size_t newsize = (numsyms + 1) * sizeof(Elf32_Sym);
+ size_t i;
+
+ if (me->symtab->data.d_buf) {
+ free(me->symtab->data.d_buf);
+ }
+ me->symtab->data.d_buf = malloc(newsize);
+ assert(me->symtab->data.d_buf);
+
+ me->symtab->data.d_size = newsize;
+ me->symtab->shdr.sh_size = newsize;
+ memset(me->symtab->data.d_buf, 0, newsize);
+
+ i = 1;
+ CIRCLEQ_FOREACH(sym, &me->symtab->symtab.syms, elem) {
+ Elf32_Sym *es = ((Elf32_Sym*)me->symtab->data.d_buf) + i;
+
+ es->st_name = sym->name;
+ es->st_value = sym->value;
+ es->st_size = sym->size;
+ es->st_info = ELF32_ST_INFO(sym->bind, sym->type);
+ es->st_other = sym->other;
+ es->st_shndx = sym->shndx;
+
+ i++;
+ }
+ } else if (me->elfclass == ELFCLASS64) {
+ size_t newsize = (numsyms + 1) * sizeof(Elf64_Sym);
+ size_t i;
+
+ if (me->symtab->data.d_buf) {
+ free(me->symtab->data.d_buf);
+ }
+ me->symtab->data.d_buf = malloc(newsize);
+ assert(me->symtab->data.d_buf);
+
+ me->symtab->data.d_size = newsize;
+ me->symtab->shdr.sh_size = newsize;
+ memset(me->symtab->data.d_buf, 0, newsize);
+
+ i = 1;
+ CIRCLEQ_FOREACH(sym, &me->symtab->symtab.syms, elem) {
+ Elf64_Sym *es = ((Elf64_Sym*)me->symtab->data.d_buf) + i;
+
+ es->st_name = sym->name;
+ es->st_value = sym->value;
+ es->st_size = sym->size;
+ es->st_info = ELF64_ST_INFO(sym->bind, sym->type);
+ es->st_other = sym->other;
+ es->st_shndx = sym->shndx;
+
+ i++;
+ }
+ } else {
+ // Unknown elfclass
+ assert(0);
+ }
+
+ elfu_mLayoutAuto(me);
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-10-16 13:27:58 +0000