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I'm using DIA Sdk to extract some information from PDB files. I create the non-com DiaSourceAlt object so I must use LocalFree to free strings.

The following piece of code works fine in x86 but, on x64, the LocalFree call corrupts the heap.

IDiaSymbol *lpSymbol;
BSTR bStrName;

...
hRes = lpSymbol->get_undecoratedNameEx(0x87FE, &bStrName);
if (SUCCEDED(hRes))
  LocalFree(bStrName);

Any suggestion? (I'm using msdia90.dll)

Regards, Mauro.

reidhoch
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Mauro H. Leggieri
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2 Answers2

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Always be careful when working with pointers. LocalAlloc increments the pointer by 4 bytes. BSTR size is word so you must only do "LocalFree(bstr - 2)".

CppNT
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After doing some reverse engineering I discovered that one MUST pass "(LPBYTE)bstr - 4" because msdia##.dll allocates using LocalAlloc and increments the pointer by four before returning data to the user.

I think this behavior is to emulate BSTR which stores the length of the string in a DWORD just before the address the pointer points to. I discovered the issue using the x64 version. In x86 although it has the same problem, app does not crash but generates a leak.

Regards.

Mauro H. Leggieri
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