src/libelfu/modelops/relocate.c

   1 #include <assert.h>
   2 #include <stdlib.h>
   3 #include <string.h>
   4 #include <libelfu/libelfu.h>
   5
   6
   7 /* Apply relocation information from section *msrt to data in
   8  * section *mstarget (which is stored in *metarget). */
   9 int elfu_mRelocate(ElfuElf *metarget, ElfuScn *mstarget, ElfuScn *msrt)
  10 {
  11   ElfuRel *rel;
  12   ElfuSym *sym;
  13
  14   assert(mstarget);
  15   assert(msrt);
  16
  17   ELFU_DEBUG("Relocating in section of type %u size %x\n",
  18              mstarget->shdr.sh_type,
  19              (unsigned)mstarget->shdr.sh_size);
  20
  21   CIRCLEQ_FOREACH(rel, &msrt->reltab.rels, elem) {
  22     Elf32_Word *dest32 = (Elf32_Word*)(mstarget->databuf + rel->offset);
  23     Elf64_Word *dest64 = (Elf64_Word*)(mstarget->databuf + rel->offset);
  24     GElf_Addr s;
  25     int haveSymval = 0;
  26
  27     sym = elfu_mSymtabIndexToSym(msrt->linkptr, rel->sym);
  28     assert(sym);
  29
  30     haveSymval = !elfu_mSymtabLookupSymToAddr(metarget,
  31                                               msrt->linkptr,
  32                                               sym,
  33                                               &s);
  34     if (!haveSymval) {
  35       if (sym->shndx == SHN_UNDEF) {
  36         haveSymval = !elfu_mDynLookupPltAddrByName(metarget,
  37                                      elfu_mSymtabSymToName(msrt->linkptr, sym),
  38                                      &s);
  39       } else if (sym->shndx == SHN_COMMON) {
  40         // TODO: Lookup in .rel.dyn
  41       }
  42     }
  43
  44     if (metarget->elfclass == ELFCLASS32) {
  45       Elf32_Word a32 = rel->addendUsed ? rel->addend : *dest32;
  46       Elf32_Addr p32 = mstarget->shdr.sh_addr + rel->offset;
  47       Elf32_Addr s32 = (Elf32_Addr)s;
  48
  49       switch(metarget->ehdr.e_machine) {
  50         case EM_386:
  51           switch(rel->type) {
  52             case R_386_NONE:
  53               ELFU_DEBUG("Skipping relocation: R_386_NONE\n");
  54               break;
  55             case R_386_32:
  56               if (!haveSymval) {
  57                 goto MISSINGSYM;
  58               }
  59               *dest32 = s32 + a32;
  60               break;
  61             case R_386_PC32:
  62               if (!haveSymval) {
  63                 goto MISSINGSYM;
  64               }
  65               *dest32 = s32 + a32 - p32;
  66               break;
  67             default:
  68               ELFU_DEBUG("elfu_mRelocate: Skipping unknown relocation type %d\n", rel->type);
  69           }
  70           break;
  71         default:
  72           ELFU_WARN("elfu_mRelocate: Unknown machine type. Aborting.\n");
  73       }
  74     } else if (metarget->elfclass == ELFCLASS64) {
  75       Elf64_Word a64 = rel->addendUsed ? rel->addend : *dest64;
  76       Elf64_Addr p64 = mstarget->shdr.sh_addr + rel->offset;
  77       Elf64_Addr s64 = (Elf64_Addr)s;
  78
  79       switch(metarget->ehdr.e_machine) {
  80         case EM_X86_64:
  81           switch(rel->type) {
  82             case R_X86_64_NONE:
  83               ELFU_DEBUG("Skipping relocation: R_386_NONE\n");
  84               break;
  85             case R_X86_64_64:
  86               if (!haveSymval) {
  87                 goto MISSINGSYM;
  88               }
  89               *dest64 = s64 + a64;
  90               break;
  91             case R_X86_64_PC32:
  92               if (!haveSymval) {
  93                 goto MISSINGSYM;
  94               }
  95               *dest32 = s64 + a64 - p64;
  96               break;
  97             case R_X86_64_32:
  98               if (!haveSymval) {
  99                 goto MISSINGSYM;
 100               }
 101               *dest32 = s64 + a64;
 102               break;
 103             default:
 104               ELFU_DEBUG("elfu_mRelocate: Skipping unknown relocation type %d", rel->type);
 105           }
 106           break;
 107         default:
 108           ELFU_WARN("elfu_mRelocate: Unknown machine type. Aborting.\n");
 109       }
 110     }
 111   }
 112
 113   return 0;
 114
 115   MISSINGSYM:
 116   ELFU_WARN("elfu_mRelocate: Could not resolve symbol %s. Aborting.\n",
 117             elfu_mSymtabSymToName(msrt->linkptr, sym));
 118   return -1;
 119
 120 }