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PODifferences in code between Windows 32 bits and 64 bits
 

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    <p>I was experimenting with the following code to simulate GetProcAddress.</p> <pre><code>// Retrieve NT header from base address. IMAGE_NT_HEADERS *GetNtHeaderFromBase( void *pBaseAddr ) { IMAGE_DOS_HEADER *pDosHeader; IMAGE_NT_HEADERS *pNtHeaders; pDosHeader = ((IMAGE_DOS_HEADER *)pBaseAddr); if(pDosHeader-&gt;e_magic != 0x5A4D) return NULL; pNtHeaders = ((IMAGE_NT_HEADERS *)((DWORD)pBaseAddr + pDosHeader-&gt;e_lfanew)); if(pNtHeaders-&gt;Signature != 0x4550) return NULL; return ((pNtHeaders == NULL) ? NULL : pNtHeaders); } // This emulates GetProcAddress. void *GetFuncAddr( DWORD pBaseAddr, char *lpszFuncName ) { IMAGE_NT_HEADERS *pNtHeaders; IMAGE_DATA_DIRECTORY *pDataDir; IMAGE_EXPORT_DIRECTORY *pExportDir; const char **lpszNames; DWORD *lpdwFuncs, dwIndex; pNtHeaders = GetNtHeaderFromBase((void *)pBaseAddr); if(pNtHeaders == NULL) return NULL; pDataDir = ((IMAGE_DATA_DIRECTORY *)(pNtHeaders-&gt;OptionalHeader.DataDirectory + IMAGE_DIRECTORY_ENTRY_EXPORT)); if(pDataDir == NULL) return NULL; pExportDir = ((IMAGE_EXPORT_DIRECTORY *)(pBaseAddr + pDataDir-&gt;VirtualAddress)); if(pExportDir == NULL) return NULL; lpdwFuncs = ((DWORD *)(pBaseAddr + pExportDir-&gt;AddressOfFunctions)); lpszNames = ((const char **)(pBaseAddr + pExportDir-&gt;AddressOfNames)); if(lpdwFuncs == NULL || lpszNames == NULL) return NULL; for(dwIndex = 0; dwIndex &lt; pExportDir-&gt;NumberOfFunctions; dwIndex++) { // decrypt funcname and get the address if(!cmpstr(((char *)(pBaseAddr + lpszNames[dwIndex])), lpszFuncName)) return (void*)(pBaseAddr + lpdwFuncs[dwIndex]); } return NULL; } </code></pre> <p>But when I run the program on a Windows Vista x64 I get an access violation. I thought it was the numbers on GetNtHeaderFromBase (the numbers passed on IMAGE_DOS_HEADER and IMAGE_NET_HEADER) but i can't find any reference anywhere as to what it might be on a x64 bit binary.</p> <p>Anyone has any idea what changes do I need to make to this code to make it work under 64 bit Windows? Or, a better way to achieve a getprocaddress-like function that works on both x32 and x64?</p> <p>Thank you for the help and the code.</p> <p>jess.</p>
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