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POAccessing contents of char** on a windows x64 cause exception
 

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  1. POAccessing contents of char** on a windows x64 cause exception
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    <p>The following piece of code is causing an exception on a windows vista x64 and i can't figure why. </p> <pre><code>size_t pBaseAddr; char *lpszFuncName; IMAGE_EXPORT_DIRECTORY *pExportDir; const char **lpszNames; unsigned int dwIndex; lpszNames = ((const char **)(pBaseAddr + pExportDir-&gt;AddressOfNames)); if(lpszNames == NULL) return NULL; for(dwIndex = 0; dwIndex &lt; pExportDir-&gt;NumberOfFunctions; dwIndex++) { if(strcmp((char *)(pBaseAddr + lpszNames[dwIndex]), lpszFuncName) == 0) return Something; } </code></pre> <p>The problem, i think, is on the strcmp() line, specifically on lpszNames[dwIndex]. It works on 32 bits but on 64 it crashes with a access violation. if you want to see the whole code <a href="https://stackoverflow.com/questions/1766031/differences-in-code-between-windows-32-bits-and-64-bits">check my previous question</a></p> <p>EDIT: since people didn't look at the link i posted on the question I will post the entire code from the original question.</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 != IMAGE_DOS_SIGNATURE) return NULL; pNtHeaders = ((IMAGE_NT_HEADERS *)((DWORD)pBaseAddr + pDosHeader-&gt;e_lfanew)); if(pNtHeaders-&gt;Signature != IMAGE_NT_SIGNATURE) return NULL; return ((pNtHeaders == NULL) ? NULL : pNtHeaders); } // This emulates GetProcAddress. void *GetFuncAddr( size_t pBaseAddr, char *lpszFuncName ) { IMAGE_NT_HEADERS *pNtHeaders; IMAGE_DATA_DIRECTORY *pDataDir; IMAGE_EXPORT_DIRECTORY *pExportDir; const char **lpszNames; size_t *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 = ((size_t *)(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(strcmp((char *)(pBaseAddr + lpszNames[dwIndex]), lpszFuncName) == 0) return (void*)(pBaseAddr + lpdwFuncs[dwIndex]); } return NULL; } </code></pre> <p>EDIT2: NO, i am NOT using DWORD.</p>
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    1. CODid you omit code? Because in the above code, `pExportDir->AddressOfNames` already invokes undefined behavior.
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    2. COWell you're not initializing pBaseAddr...
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    3. COpBaseAddress is being passed as an argument to the function. That's why I placed a link to the original code.
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      1. USJessica
 

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