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POdynamic load on Windows 7 fails
 

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    <p>As I mentioned on one my previous questions I am playing with simulating GetProcAddress() in my code. The following code is successful in doing this, however it causes the application to crash on windows 7</p> <pre><code>void *GetFuncAddr(HMODULE hModule, char *fname) { unsigned int count = 1; IMAGE_DOS_HEADER *DosHeader; IMAGE_NT_HEADERS *NtHeaders; IMAGE_OPTIONAL_HEADER *OptionalHeader; IMAGE_DATA_DIRECTORY *DataDirectory; IMAGE_EXPORT_DIRECTORY *Exp; ULONG *addrof; char *fullfname; ULONG *faddr; DosHeader = (IMAGE_DOS_HEADER *)hModule; if (DosHeader-&gt;e_magic != IMAGE_DOS_SIGNATURE) { return NULL; } NtHeaders = (IMAGE_NT_HEADERS *)(((BYTE *)DosHeader) + DosHeader-&gt;e_lfanew); if (NtHeaders-&gt;Signature != IMAGE_NT_SIGNATURE) { return NULL; } OptionalHeader = &amp;NtHeaders-&gt;OptionalHeader; DataDirectory = &amp;OptionalHeader-&gt;DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT]; Exp = (IMAGE_EXPORT_DIRECTORY *)((size_t)DosHeader + DataDirectory-&gt;VirtualAddress); addrof = (ULONG *)((BYTE*) hModule + Exp-&gt;addrof); faddr = (ULONG*) ((BYTE*) hModule + Exp-&gt;AddressOfFunctions); for(count = 0; count &lt; Exp-&gt;NumberOfNames; count++) { fullfname = (char*)((BYTE*) hModule + addrof[count]); if(strcmp(fullfname, fname) == 0) { return (void*)((BYTE*) hModule + faddr[count]); } } return NULL; } </code></pre> <p>It doesn't matter what function I tried loading using this the application crashes. The crashes occurs when calling the imported function so my guess is that the pointer returned might be the offending thing here. This occurs on both x86 and x64. Is there any visible reason for this in this code?</p> <p>I tried setting the function to return FARPROC but I'm getting all confused about how to cast the return on ((BYTE*) hModule + faddr[count]);</p> <p>Anyway, any ideas? solutions? Any help is appreciated.</p> <p>Thanks. jess.</p> <p><strong>EDIT</strong> The error returned by some of the API's i am importing is error 18, the parameter is incorrect.</p>
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    1. COFirst, FARPROC is irrelevant as this is a legacy from 16-bit times when FAR (off-segment) or NEAR (intersegment) addresses were used. What is the value of your pointer? Always ASSERT(ptr) !
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    2. COThanks for the information. I am asserting on the pointer on the calling function. If the pointer is null i'm flagging an error and terminate the program. The pointer, however, seem to be OK
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    3. COMaybe you are being hit by base address randomization? Does it fail for dlls you built yourself?
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