3 * ELF Executable Loader Code
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13 #define DEBUG_WARN 1
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19 // === PROTOTYPES ===
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20 int Elf_Load(int fd);
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21 int Elf_Relocate(void *Base);
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22 int Elf_GetSymbol(void *Base, char *Name, intptr_t *ret);
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23 int Elf_Int_DoRelocate(uint32_t r_info, uint32_t *ptr, uint32_t addend, Elf32_Sym *symtab, intptr_t base);
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24 uint32_t Elf_Int_HashString(char *str);
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27 int Elf_Load(int FD)
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33 uint32_t max, base = -1;
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39 read(FD, &hdr, sizeof(hdr));
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41 // Check the file type
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42 if(hdr.ident[0] != 0x7F || hdr.ident[1] != 'E' || hdr.ident[2] != 'L' || hdr.ident[3] != 'F') {
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43 Warning("Non-ELF File was passed to the ELF loader\n");
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48 // Check for a program header
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49 if(hdr.phoff == 0) {
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51 Warning("ELF File does not contain a program header\n");
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57 // Read Program Header Table
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58 phtab = malloc( sizeof(Elf32_Phdr) * hdr.phentcount );
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63 LOG("hdr.phoff = 0x%08x", hdr.phoff);
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64 lseek(FD, hdr.phoff, SEEK_SET);
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65 read(FD, phtab, sizeof(Elf32_Phdr)*hdr.phentcount);
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69 LOG("hdr.phentcount = %i", hdr.phentcount);
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70 for( i = 0; i < hdr.phentcount; i++ )
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72 // Ignore Non-LOAD types
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73 if(phtab[i].Type != PT_LOAD)
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75 iPageCount += ((phtab[i].VAddr&0xFFF) + phtab[i].MemSize + 0xFFF) >> 12;
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76 LOG("phtab[%i] = {VAddr:0x%x, MemSize:0x%x}", i, phtab[i].VAddr, phtab[i].MemSize);
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79 LOG("iPageCount = %i", iPageCount);
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81 // Allocate Information Structure
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82 //ret = malloc( sizeof(tBinary) + sizeof(tBinaryPage)*iPageCount );
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84 //ret->Entry = hdr.entrypoint;
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85 //ret->Base = -1; // Set Base to maximum value
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86 //ret->NumPages = iPageCount;
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87 //ret->Interpreter = NULL;
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89 // Prescan for base and size
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90 for( i = 0; i < hdr.phentcount; i ++)
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92 if( phtab[i].Type != PT_LOAD )
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94 if( phtab[i].VAddr < base )
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95 base = phtab[i].VAddr;
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96 if( phtab[i].VAddr > max )
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97 max = phtab[i].VAddr;
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100 LOG("base = %08x, max = %08x", base, max);
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104 for( i = 0; i < hdr.phentcount; i++ )
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106 //LOG("phtab[%i].Type = 0x%x", i, phtab[i].Type);
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107 LOG("phtab[%i] = {", i);
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108 LOG(" .Type = 0x%08x", phtab[i].Type);
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109 LOG(" .Offset = 0x%08x", phtab[i].Offset);
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110 LOG(" .VAddr = 0x%08x", phtab[i].VAddr);
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111 LOG(" .PAddr = 0x%08x", phtab[i].PAddr);
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112 LOG(" .FileSize = 0x%08x", phtab[i].FileSize);
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113 LOG(" .MemSize = 0x%08x", phtab[i].MemSize);
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114 LOG(" .Flags = 0x%08x", phtab[i].Flags);
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115 LOG(" .Align = 0x%08x", phtab[i].Align);
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117 // Get Interpreter Name
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118 if( phtab[i].Type == PT_INTERP )
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121 //if(ret->Interpreter) continue;
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122 tmp = malloc(phtab[i].FileSize);
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123 lseek(FD, phtab[i].Offset, 1);
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124 read(FD, tmp, phtab[i].FileSize);
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125 //ret->Interpreter = Binary_RegInterp(tmp);
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126 LOG("Interpreter '%s'", tmp);
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130 // Ignore non-LOAD types
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131 if(phtab[i].Type != PT_LOAD) continue;
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133 LOG("phtab[%i] = {VAddr:0x%x,Offset:0x%x,FileSize:0x%x}",
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134 i, phtab[i].VAddr, phtab[i].Offset, phtab[i].FileSize);
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136 addr = phtab[i].VAddr;
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138 AllocateMemory( addr, phtab[i].MemSize );
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140 lseek(FD, phtab[i].Offset, SEEK_SET);
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141 read(FD, (void*)(intptr_t)addr, phtab[i].FileSize);
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142 memset( (char*)(intptr_t)addr + phtab[i].FileSize, 0, phtab[i].MemSize - phtab[i].FileSize);
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152 // --- ELF RELOCATION ---
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154 \fn int Elf_Relocate(void *Base)
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155 \brief Relocates a loaded ELF Executable
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157 int Elf_Relocate(void *Base)
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159 Elf32_Ehdr *hdr = Base;
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161 int i, j; // Counters
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163 uint32_t iRealBase = -1;
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164 intptr_t iBaseDiff;
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167 Elf32_Rel *rel = NULL;
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168 Elf32_Rela *rela = NULL;
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169 uint32_t *pltgot = NULL;
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172 int relSz=0, relEntSz=8;
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173 int relaSz=0, relaEntSz=8;
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174 int pltSz=0, pltType=0;
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175 Elf32_Dyn *dynamicTab = NULL; // Dynamic Table Pointer
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176 char *dynstrtab = NULL; // .dynamic String Table
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177 Elf32_Sym *dynsymtab = NULL;
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180 ENTER("pBase", Base);
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182 // Parse Program Header to get Dynamic Table
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183 phtab = Base + hdr->phoff;
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184 iSegmentCount = hdr->phentcount;
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185 for(i = 0; i < iSegmentCount; i ++ )
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187 // Determine linked base address
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188 if(phtab[i].Type == PT_LOAD && iRealBase > phtab[i].VAddr)
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189 iRealBase = phtab[i].VAddr;
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191 // Find Dynamic Section
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192 if(phtab[i].Type == PT_DYNAMIC) {
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194 Warning("Elf_Relocate - Multiple PT_DYNAMIC segments\n");
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197 dynamicTab = (void *) (intptr_t) phtab[i].VAddr;
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198 j = i; // Save Dynamic Table ID
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203 // Check if a PT_DYNAMIC segement was found
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205 Warning("Elf_Relocate: No PT_DYNAMIC segment in image, returning\n");
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206 LEAVE('x', hdr->entrypoint);
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207 return hdr->entrypoint;
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210 // Page Align real base
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211 iRealBase &= ~0xFFF;
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213 // Adjust "Real" Base
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214 iBaseDiff = (intptr_t)Base - iRealBase;
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215 // Adjust Dynamic Table
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216 dynamicTab = (void *) ((intptr_t)dynamicTab + iBaseDiff);
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218 // === Get Symbol table and String Table ===
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219 for( j = 0; dynamicTab[j].d_tag != DT_NULL; j++)
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221 switch(dynamicTab[j].d_tag)
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223 // --- Symbol Table ---
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225 dynamicTab[j].d_val += iBaseDiff;
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226 dynsymtab = (void*) (intptr_t) dynamicTab[j].d_val;
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227 hdr->misc.SymTable = dynamicTab[j].d_val; // Saved in unused bytes of ident
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230 // --- String Table ---
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232 dynamicTab[j].d_val += iBaseDiff;
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233 dynstrtab = (void*) (intptr_t) dynamicTab[j].d_val;
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236 // --- Hash Table --
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238 dynamicTab[j].d_val += iBaseDiff;
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239 iSymCount = ((uint32_t*)((intptr_t)dynamicTab[j].d_val))[1];
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240 hdr->misc.HashTable = dynamicTab[j].d_val; // Saved in unused bytes of ident
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246 // Alter Symbols to true base
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247 for(i = 0; i < iSymCount; i ++)
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249 dynsymtab[i].value += iBaseDiff;
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250 dynsymtab[i].nameOfs += (intptr_t)dynstrtab;
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251 //LOG("Sym '%s' = 0x%x (relocated)\n", dynsymtab[i].name, dynsymtab[i].value);
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254 // === Add to loaded list (can be imported now) ===
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255 //Binary_AddLoaded( (intptr_t)Base );
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257 // === Parse Relocation Data ===
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258 for( j = 0; dynamicTab[j].d_tag != DT_NULL; j++)
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260 switch(dynamicTab[j].d_tag)
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262 // --- Shared Library Name ---
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264 LOG(".so Name '%s'\n", dynstrtab+dynamicTab[j].d_val);
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266 // --- Needed Library ---
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268 libPath = dynstrtab + dynamicTab[j].d_val;
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269 Notice("%p - Required Library '%s' - TODO load DT_NEEDED\n", Base, libPath);
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272 case DT_PLTGOT: pltgot = (void*)(iBaseDiff+dynamicTab[j].d_val); break;
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273 case DT_JMPREL: plt = (void*)(iBaseDiff+dynamicTab[j].d_val); break;
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274 case DT_PLTREL: pltType = dynamicTab[j].d_val; break;
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275 case DT_PLTRELSZ: pltSz = dynamicTab[j].d_val; break;
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277 // --- Relocation ---
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278 case DT_REL: rel = (void*)(iBaseDiff + dynamicTab[j].d_val); break;
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279 case DT_RELSZ: relSz = dynamicTab[j].d_val; break;
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280 case DT_RELENT: relEntSz = dynamicTab[j].d_val; break;
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282 case DT_RELA: rela = (void*)(iBaseDiff + dynamicTab[j].d_val); break;
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283 case DT_RELASZ: relaSz = dynamicTab[j].d_val; break;
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284 case DT_RELAENT: relaEntSz = dynamicTab[j].d_val; break;
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288 // Parse Relocation Entries
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291 j = relSz / relEntSz;
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292 for( i = 0; i < j; i++ )
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294 ptr = (void*)(iBaseDiff + rel[i].r_offset);
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295 if( !Elf_Int_DoRelocate(rel[i].r_info, ptr, *ptr, dynsymtab, (intptr_t)Base) ) {
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300 // Parse Relocation Entries
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303 j = relaSz / relaEntSz;
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304 for( i = 0; i < j; i++ )
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306 ptr = (void*)(iBaseDiff + rela[i].r_offset);
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307 if( !Elf_Int_DoRelocate(rel[i].r_info, ptr, rela[i].r_addend, dynsymtab, (intptr_t)Base) ) {
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313 // === Process PLT (Procedure Linkage Table) ===
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316 if(pltType == DT_REL)
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318 Elf32_Rel *pltRel = plt;
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319 j = pltSz / sizeof(Elf32_Rel);
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320 LOG("PLT Rel - plt = %p, pltSz = %i (%i ents)", plt, pltSz, j);
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321 for(i = 0; i < j; i++)
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323 ptr = (void*)(iBaseDiff + pltRel[i].r_offset);
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324 if( !Elf_Int_DoRelocate(pltRel[i].r_info, ptr, *ptr, dynsymtab, (intptr_t)Base) ) {
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331 Elf32_Rela *pltRela = plt;
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332 j = pltSz / sizeof(Elf32_Rela);
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333 LOG("PLT RelA - plt = %p, pltSz = %i (%i ents)", plt, pltSz, j);
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336 ptr = (void*)(iBaseDiff + pltRela[i].r_offset);
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337 if( !Elf_Int_DoRelocate(pltRela[i].r_info, ptr, pltRela[i].r_addend, dynsymtab, (intptr_t)Base) ) {
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349 LEAVE('x', hdr->entrypoint);
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350 return hdr->entrypoint;
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354 * \fn void Elf_Int_DoRelocate(uint32_t r_info, uint32_t *ptr, uint32_t addend, Elf32_Sym *symtab, uint32_t base)
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355 * \brief Performs a relocation
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356 * \param r_info Field from relocation entry
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357 * \param ptr Pointer to location of relocation
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358 * \param addend Value to add to symbol
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359 * \param symtab Symbol Table
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360 * \param base Base of loaded binary
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362 int Elf_Int_DoRelocate(uint32_t r_info, uint32_t *ptr, uint32_t addend, Elf32_Sym *symtab, intptr_t base)
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365 int type = ELF32_R_TYPE(r_info);
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366 int sym = ELF32_R_SYM(r_info);
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367 char *sSymName = symtab[sym].name;
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369 //LogF("Elf_Int_DoRelocate: (r_info=0x%x, ptr=0x%x, addend=0x%x, .., base=0x%x)\n",
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370 // r_info, ptr, addend, base);
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374 // Standard 32 Bit Relocation (S+A)
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376 if( !Elf_GetSymbol((void*)base, sSymName, &val) ) // Search this binary first
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377 if( !Binary_GetSymbol( sSymName, &val ) )
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379 LOG("%08x R_386_32 *0x%x += 0x%x('%s')", r_info, ptr, val, sSymName);
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380 *ptr = val + addend;
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383 // 32 Bit Relocation wrt. Offset (S+A-P)
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385 if( !Elf_GetSymbol( (void*)base, sSymName, &val ) )
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386 if( !Binary_GetSymbol( sSymName, &val ) )
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388 LOG("%08x R_386_PC32 *0x%x = 0x%x + 0x%x('%s') - %p", r_info, ptr, *ptr, val, sSymName, ptr );
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389 // TODO: Check if it needs the true value of ptr or the compiled value
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390 // NOTE: Testing using true value
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391 *ptr = val + addend - (intptr_t)ptr;
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394 // Absolute Value of a symbol (S)
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395 case R_386_GLOB_DAT:
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396 if( !Elf_GetSymbol( (void*)base, sSymName, &val ) )
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397 if( !Binary_GetSymbol( sSymName, &val ) )
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399 LOG("%08x R_386_GLOB_DAT *0x%x = 0x%x (%s)", r_info, ptr, val, sSymName);
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403 // Absolute Value of a symbol (S)
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404 case R_386_JMP_SLOT:
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405 if( !Elf_GetSymbol( (void*)base, sSymName, &val ) )
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406 if( !Binary_GetSymbol( sSymName, &val ) )
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408 LOG("%08x R_386_JMP_SLOT %p = 0x%x (%s)", r_info, ptr, val, sSymName);
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412 // Base Address (B+A)
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413 case R_386_RELATIVE:
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414 LOG("%08x R_386_RELATIVE %p = 0x%x + 0x%x", r_info, ptr, base, addend);
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415 *ptr = base + addend;
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419 LOG("Rel 0x%x: 0x%x,%i", ptr, sym, type);
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426 * \fn int Elf_GetSymbol(void *Base, char *name, intptr_t *ret)
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427 * \brief Get a symbol from the loaded binary
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429 int Elf_GetSymbol(void *Base, char *Name, intptr_t *ret)
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431 Elf32_Ehdr *hdr = (void*)Base;
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436 uint32_t *pBuckets;
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438 uint32_t iNameHash;
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440 if(!Base) return 0;
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442 pBuckets = (void *)(intptr_t) hdr->misc.HashTable;
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443 symtab = (void *)(intptr_t) hdr->misc.SymTable;
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445 nbuckets = pBuckets[0];
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446 iSymCount = pBuckets[1];
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447 pBuckets = &pBuckets[2];
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448 pChains = &pBuckets[ nbuckets ];
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451 iNameHash = Elf_Int_HashString(Name);
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452 iNameHash %= nbuckets;
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455 i = pBuckets[ iNameHash ];
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456 if(symtab[i].shndx != SHN_UNDEF && strcmp(symtab[i].name, Name) == 0) {
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457 if(ret) *ret = symtab[ i ].value;
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462 while(pChains[i] != STN_UNDEF)
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465 if(symtab[i].shndx != SHN_UNDEF && strcmp(symtab[ i ].name, Name) == 0) {
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466 if(ret) *ret = symtab[ i ].value;
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474 * \fn uint32_t Elf_Int_HashString(char *str)
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475 * \brief Hash a string in the ELF format
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476 * \param str String to hash
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477 * \return Hash value
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479 uint32_t Elf_Int_HashString(char *str)
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484 h = (h << 4) + *str++;
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485 if( (g = h & 0xf0000000) )
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