3 * ELF Executable Loader Code
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13 #define DEBUG_WARN 1
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15 #define MKPTR(_type,_val) ((_type*)(uintptr_t)(_val))
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16 #define PTRMK(_type,_val) MKPTR(_type,_val)
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17 #define PTR(_val) ((void*)(uintptr_t)(_val))
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21 # define LOG(s, ...) printf("%s: " s, __func__, __VA_ARGS__)
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22 # define LOGS(s) printf("%s: " s, __func__)
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31 // === PROTOTYPES ===
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32 void *Elf_Load(FILE *FP);
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33 uintptr_t Elf_Relocate(void *Base);
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34 int Elf_GetSymbol(void *Base, char *Name, uintptr_t *ret);
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35 int Elf_Int_DoRelocate(uint32_t r_info, uint32_t *ptr, uint32_t addend, Elf32_Sym *symtab, void *Base);
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36 uint32_t Elf_Int_HashString(char *str);
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39 void *Elf_Load(FILE *FP)
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45 uint32_t max, base = -1;
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47 uint32_t baseDiff = 0;
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52 fread(&hdr, sizeof(hdr), 1, FP);
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54 // Check the file type
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55 if(hdr.ident[0] != 0x7F || hdr.ident[1] != 'E' || hdr.ident[2] != 'L' || hdr.ident[3] != 'F') {
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56 Warning("Non-ELF File was passed to the ELF loader\n");
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61 // Check for a program header
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62 if(hdr.phoff == 0) {
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64 Warning("ELF File does not contain a program header\n");
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70 // Read Program Header Table
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71 phtab = malloc( sizeof(Elf32_Phdr) * hdr.phentcount );
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76 LOG("hdr.phoff = 0x%08x\n", hdr.phoff);
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77 fseek(FP, hdr.phoff, SEEK_SET);
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78 fread(phtab, sizeof(Elf32_Phdr), hdr.phentcount, FP);
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82 LOG("hdr.phentcount = %i\n", hdr.phentcount);
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83 for( i = 0; i < hdr.phentcount; i++ )
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85 // Ignore Non-LOAD types
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86 if(phtab[i].Type != PT_LOAD)
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88 iPageCount += ((phtab[i].VAddr&0xFFF) + phtab[i].MemSize + 0xFFF) >> 12;
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89 LOG("phtab[%i] = {VAddr:0x%x, MemSize:0x%x}\n", i, phtab[i].VAddr, phtab[i].MemSize);
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92 LOG("iPageCount = %i\n", iPageCount);
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94 // Allocate Information Structure
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95 //ret = malloc( sizeof(tBinary) + sizeof(tBinaryPage)*iPageCount );
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97 //ret->Entry = hdr.entrypoint;
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98 //ret->Base = -1; // Set Base to maximum value
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99 //ret->NumPages = iPageCount;
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100 //ret->Interpreter = NULL;
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102 // Prescan for base and size
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103 for( i = 0; i < hdr.phentcount; i ++)
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105 if( phtab[i].Type != PT_LOAD )
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107 if( phtab[i].VAddr < base )
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108 base = phtab[i].VAddr;
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109 if( phtab[i].VAddr > max )
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110 max = phtab[i].VAddr;
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113 LOG("base = %08x, max = %08x\n", base, max);
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116 // Find a nice space (31 address bits allowed)
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117 base = FindFreeRange( max, 31 );
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118 LOG("new base = %08x\n", base);
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119 if( base == 0 ) return NULL;
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125 for( i = 0; i < hdr.phentcount; i++ )
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127 //LOG("phtab[%i].Type = 0x%x", i, phtab[i].Type);
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128 LOG("phtab[%i] = {\n", i);
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129 LOG(" .Type = 0x%08x\n", phtab[i].Type);
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130 LOG(" .Offset = 0x%08x\n", phtab[i].Offset);
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131 LOG(" .VAddr = 0x%08x\n", phtab[i].VAddr);
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132 LOG(" .PAddr = 0x%08x\n", phtab[i].PAddr);
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133 LOG(" .FileSize = 0x%08x\n", phtab[i].FileSize);
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134 LOG(" .MemSize = 0x%08x\n", phtab[i].MemSize);
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135 LOG(" .Flags = 0x%08x\n", phtab[i].Flags);
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136 LOG(" .Align = 0x%08x\n", phtab[i].Align);
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138 // Get Interpreter Name
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139 if( phtab[i].Type == PT_INTERP )
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142 //if(ret->Interpreter) continue;
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143 tmp = malloc(phtab[i].FileSize);
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144 fseek(FP, phtab[i].Offset, SEEK_SET);
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145 fread(tmp, phtab[i].FileSize, 1, FP);
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146 //ret->Interpreter = Binary_RegInterp(tmp);
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147 LOG("Interpreter '%s'\n", tmp);
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151 // Ignore non-LOAD types
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152 if(phtab[i].Type != PT_LOAD) continue;
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154 LOG("phtab[%i] = {VAddr:0x%x,Offset:0x%x,FileSize:0x%x}\n",
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155 i, phtab[i].VAddr+baseDiff, phtab[i].Offset, phtab[i].FileSize);
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157 addr = phtab[i].VAddr + baseDiff;
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159 if( AllocateMemory( addr, phtab[i].MemSize ) ) {
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163 fseek(FP, phtab[i].Offset, SEEK_SET);
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164 fread( PTRMK(void, addr), phtab[i].FileSize, 1, FP );
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165 memset( PTRMK(char, addr) + phtab[i].FileSize, 0, phtab[i].MemSize - phtab[i].FileSize );
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172 return PTRMK(void, base);
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175 // --- ELF RELOCATION ---
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177 * \brief Relocates a loaded ELF Executable
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179 uintptr_t Elf_Relocate(void *Base)
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181 Elf32_Ehdr *hdr = Base;
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183 int i, j; // Counters
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185 uint32_t iRealBase = -1;
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186 uintptr_t iBaseDiff;
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189 Elf32_Rel *rel = NULL;
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190 Elf32_Rela *rela = NULL;
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191 uint32_t *pltgot = NULL;
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194 int relSz=0, relEntSz=8;
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195 int relaSz=0, relaEntSz=8;
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196 int pltSz=0, pltType=0;
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197 Elf32_Dyn *dynamicTab = NULL; // Dynamic Table Pointer
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198 char *dynstrtab = NULL; // .dynamic String Table
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199 Elf32_Sym *dynsymtab = NULL;
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202 ENTER("pBase", Base);
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203 LOG("Base = %p\n", Base);
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205 // Parse Program Header to get Dynamic Table
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206 phtab = Base + hdr->phoff;
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207 iSegmentCount = hdr->phentcount;
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208 for(i = 0; i < iSegmentCount; i ++ )
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210 // Determine linked base address
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211 if(phtab[i].Type == PT_LOAD && iRealBase > phtab[i].VAddr)
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212 iRealBase = phtab[i].VAddr;
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214 // Find Dynamic Section
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215 if(phtab[i].Type == PT_DYNAMIC) {
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217 Warning("Elf_Relocate - Multiple PT_DYNAMIC segments\n");
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220 dynamicTab = MKPTR(void, phtab[i].VAddr);
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221 j = i; // Save Dynamic Table ID
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226 // Check if a PT_DYNAMIC segement was found
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228 Warning("Elf_Relocate: No PT_DYNAMIC segment in image, returning\n");
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229 LEAVE('x', hdr->entrypoint);
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230 return hdr->entrypoint;
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233 // Page Align real base
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234 iRealBase &= ~0xFFF;
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236 LOG("dynamicTab = %p\n", dynamicTab);
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237 // Adjust "Real" Base
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238 iBaseDiff = (uintptr_t)Base - iRealBase;
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239 LOG("iBaseDiff = %p\n", (void*)iBaseDiff);
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240 // Adjust Dynamic Table
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241 dynamicTab = PTR( (uintptr_t)dynamicTab + iBaseDiff);
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242 LOG("dynamicTab = %p\n", dynamicTab);
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244 hdr->entrypoint += iBaseDiff;
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246 // === Get Symbol table and String Table ===
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247 for( j = 0; dynamicTab[j].d_tag != DT_NULL; j++)
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249 switch(dynamicTab[j].d_tag)
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251 // --- Symbol Table ---
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253 dynamicTab[j].d_val += iBaseDiff;
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254 dynsymtab = PTRMK(void, dynamicTab[j].d_val);
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255 hdr->misc.SymTable = dynamicTab[j].d_val; // Saved in unused bytes of ident
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258 // --- String Table ---
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260 dynamicTab[j].d_val += iBaseDiff;
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261 dynstrtab = PTRMK(void, dynamicTab[j].d_val);
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264 // --- Hash Table --
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266 dynamicTab[j].d_val += iBaseDiff;
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267 iSymCount = (PTRMK(uint32_t, dynamicTab[j].d_val))[1];
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268 hdr->misc.HashTable = dynamicTab[j].d_val; // Saved in unused bytes of ident
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274 // Alter Symbols to true base
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275 for(i = 0; i < iSymCount; i ++)
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277 dynsymtab[i].value += iBaseDiff;
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278 dynsymtab[i].nameOfs += (uintptr_t)dynstrtab;
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279 LOG("Sym '%s' = 0x%x (relocated)\n", MKPTR(char,dynsymtab[i].name), dynsymtab[i].value);
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282 // === Add to loaded list (can be imported now) ===
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283 Binary_SetReadyToUse( Base );
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285 // === Parse Relocation Data ===
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286 for( j = 0; dynamicTab[j].d_tag != DT_NULL; j++)
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288 switch(dynamicTab[j].d_tag)
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290 // --- Shared Library Name ---
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292 LOG(".so Name '%s'\n", dynstrtab + dynamicTab[j].d_val);
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294 // --- Needed Library ---
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296 libPath = dynstrtab + dynamicTab[j].d_val;
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297 Binary_LoadLibrary(libPath);
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300 case DT_PLTGOT: pltgot = (void*)(iBaseDiff+dynamicTab[j].d_val); break;
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301 case DT_JMPREL: plt = (void*)(iBaseDiff+dynamicTab[j].d_val); break;
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302 case DT_PLTREL: pltType = dynamicTab[j].d_val; break;
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303 case DT_PLTRELSZ: pltSz = dynamicTab[j].d_val; break;
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305 // --- Relocation ---
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306 case DT_REL: rel = (void*)(iBaseDiff + dynamicTab[j].d_val); break;
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307 case DT_RELSZ: relSz = dynamicTab[j].d_val; break;
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308 case DT_RELENT: relEntSz = dynamicTab[j].d_val; break;
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310 case DT_RELA: rela = (void*)(iBaseDiff + dynamicTab[j].d_val); break;
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311 case DT_RELASZ: relaSz = dynamicTab[j].d_val; break;
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312 case DT_RELAENT: relaEntSz = dynamicTab[j].d_val; break;
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316 // Parse Relocation Entries
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319 j = relSz / relEntSz;
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320 for( i = 0; i < j; i++ )
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322 ptr = (void*)(iBaseDiff + rel[i].r_offset);
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323 if( !Elf_Int_DoRelocate(rel[i].r_info, ptr, *ptr, dynsymtab, Base) ) {
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328 // Parse Relocation Entries
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331 j = relaSz / relaEntSz;
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332 for( i = 0; i < j; i++ )
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334 ptr = (void*)(iBaseDiff + rela[i].r_offset);
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335 if( !Elf_Int_DoRelocate(rel[i].r_info, ptr, rela[i].r_addend, dynsymtab, Base) ) {
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341 // === Process PLT (Procedure Linkage Table) ===
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344 if(pltType == DT_REL)
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346 Elf32_Rel *pltRel = plt;
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347 j = pltSz / sizeof(Elf32_Rel);
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348 LOG("PLT Rel - plt = %p, pltSz = %i (%i ents)\n", plt, pltSz, j);
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349 for(i = 0; i < j; i++)
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351 ptr = (void*)(iBaseDiff + pltRel[i].r_offset);
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352 if( !Elf_Int_DoRelocate(pltRel[i].r_info, ptr, *ptr, dynsymtab, Base) ) {
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359 Elf32_Rela *pltRela = plt;
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360 j = pltSz / sizeof(Elf32_Rela);
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361 LOG("PLT RelA - plt = %p, pltSz = %i (%i ents)\n", plt, pltSz, j);
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364 ptr = (void*)(iBaseDiff + pltRela[i].r_offset);
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365 if( !Elf_Int_DoRelocate(pltRela[i].r_info, ptr, pltRela[i].r_addend, dynsymtab, Base) ) {
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377 LEAVE('x', hdr->entrypoint);
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378 return hdr->entrypoint;
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382 * \fn void Elf_Int_DoRelocate(uint32_t r_info, uint32_t *ptr, uint32_t addend, Elf32_Sym *symtab, void *base)
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383 * \brief Performs a relocation
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384 * \param r_info Field from relocation entry
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385 * \param ptr Pointer to location of relocation
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386 * \param addend Value to add to symbol
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387 * \param symtab Symbol Table
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388 * \param base Base of loaded binary
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390 int Elf_Int_DoRelocate(uint32_t r_info, uint32_t *ptr, uint32_t addend, Elf32_Sym *symtab, void *base)
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393 int type = ELF32_R_TYPE(r_info);
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394 int sym = ELF32_R_SYM(r_info);
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395 char *sSymName = PTRMK(char, symtab[sym].name);
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397 //LogF("Elf_Int_DoRelocate: (r_info=0x%x, ptr=0x%x, addend=0x%x, .., base=0x%x)\n",
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398 // r_info, ptr, addend, base);
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402 // Standard 32 Bit Relocation (S+A)
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404 if( !Elf_GetSymbol( base, sSymName, &val ) && !Binary_GetSymbol( sSymName, &val ) ) {
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405 Warning("Unable to find symbol '%s'", sSymName);
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408 LOG("%08x R_386_32 *%p += %p('%s')\n", r_info, ptr, (void*)val, sSymName);
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409 *ptr = val + addend;
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412 // 32 Bit Relocation wrt. Offset (S+A-P)
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414 if( !Elf_GetSymbol( base, sSymName, &val ) && !Binary_GetSymbol( sSymName, &val ) ) {
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415 Warning("Unable to find symbol '%s'", sSymName);
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418 LOG("%08x R_386_PC32 *%p = 0x%x + %p('%s') - %p\n", r_info, ptr, *ptr, (void*)val, sSymName, ptr );
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419 // TODO: Check if it needs the true value of ptr or the compiled value
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420 // NOTE: Testing using true value
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421 *ptr = val + addend - (uintptr_t)ptr;
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424 // Absolute Value of a symbol (S)
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425 case R_386_GLOB_DAT:
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426 if( !Elf_GetSymbol( base, sSymName, &val ) && !Binary_GetSymbol( sSymName, &val ) ) {
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427 Warning("Unable to find symbol '%s'", sSymName);
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430 LOG("%08x R_386_GLOB_DAT *%p = 0x%x(%s)\n", r_info, ptr, (unsigned int)val, sSymName);
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434 // Absolute Value of a symbol (S)
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435 case R_386_JMP_SLOT:
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436 if( !Elf_GetSymbol( base, sSymName, &val ) && !Binary_GetSymbol( sSymName, &val ) ) {
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437 Warning("Unable to find symbol '%s'", sSymName);
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440 LOG("%08x R_386_JMP_SLOT *%p = 0x%x (%s)\n", r_info, ptr, (unsigned int)val, sSymName);
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444 // Base Address (B+A)
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445 case R_386_RELATIVE:
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446 LOG("%08x R_386_RELATIVE *%p = %p + 0x%x\n", r_info, ptr, base, addend);
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447 *ptr = (uintptr_t)base + addend;
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451 LOG("Rel %p: 0x%x,%i\n", ptr, sym, type);
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458 * \fn int Elf_GetSymbol(void *Base, char *name, uintptr_t *ret)
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459 * \brief Get a symbol from the loaded binary
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461 int Elf_GetSymbol(void *Base, char *Name, uintptr_t *ret)
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463 Elf32_Ehdr *hdr = (void*)Base;
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468 uint32_t *pBuckets;
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470 uint32_t iNameHash;
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472 if(!Base) return 0;
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474 pBuckets = PTR(hdr->misc.HashTable);
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475 symtab = PTR(hdr->misc.SymTable);
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477 nbuckets = pBuckets[0];
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478 iSymCount = pBuckets[1];
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479 pBuckets = &pBuckets[2];
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480 pChains = &pBuckets[ nbuckets ];
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483 iNameHash = Elf_Int_HashString(Name);
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484 iNameHash %= nbuckets;
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487 i = pBuckets[ iNameHash ];
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488 if(symtab[i].shndx != SHN_UNDEF && strcmp(MKPTR(char,symtab[i].name), Name) == 0) {
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489 if(ret) *ret = symtab[ i ].value;
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494 while(pChains[i] != STN_UNDEF)
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497 if(symtab[i].shndx != SHN_UNDEF && strcmp(MKPTR(char,symtab[i].name), Name) == 0) {
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498 if(ret) *ret = symtab[ i ].value;
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506 * \fn uint32_t Elf_Int_HashString(char *str)
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507 * \brief Hash a string in the ELF format
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508 * \param str String to hash
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509 * \return Hash value
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511 uint32_t Elf_Int_HashString(char *str)
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516 h = (h << 4) + *str++;
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517 if( (g = h & 0xf0000000) )
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