Re: Excessive "fd" bytes at its tail of heap allocation

From:
"Igor Tandetnik" <itandetnik@mvps.org>
Newsgroups:
microsoft.public.vc.language
Date:
Fri, 18 Dec 2009 08:45:27 -0500
Message-ID:
<e9ijeh#fKHA.3792@TK2MSFTNGP02.phx.gbl>
Jack wrote:

[code]
HRESULT CMesh::LoadMesh(const char *szfilename)
{
 
   char szPath[1024];
  CAllocateHierarchy Alloc;
PBYTE pMappedFileBase = NULL;
 
 
 
// unload these functions to a dll

GetModuleFileNameA(NULL, szPath, sizeof(szPath));

 
strcat (szPath, szfilename);
 
 
 FILE *fp = fopen (szPath, "rb");


Does this succeed? szPath currently contains something like

c:\somepath\yourapp.exesomefilename

This is unlikely to refer to an actual file.

if (fp == NULL)
 OutputDebugStringA("File open error\n");
__int64 si = FileSize64(szPath);


What's the value of si here? If szPath is in fact invalid, it's probably =
zeo.

int actlen = si-4;


And if si is zero, then actlen (when cast to unsigned int) is a very =
large value.

 int size_template = sizeof(template_bin);


What's template_bin?

 int j = actlen+size_template;
 
 
std::vector<BYTE> v2(j);
   PBYTE pBin = &v2[0];
 
 int x;
for (x = 0; x < size_template; x++)
{
 pBin[x] = template_bin[x];
}
 
 
int i = 0;
for (; x < j;x++,i++)
{
 
 pBin[x] = pMappedFileBase[i];
}
assert(x == j);


It appears that these two loops can be replaced with this:

memcpy(pBin, template_bin, size_template);
memcpy(pBin + size_template, pMappedFileBase, actlen);

// Build a new parser?
hr = D3DXLoadMeshHierarchyFromXInMemory((LPCVOID) pBin, j,
D3DXMESH_MANAGED, m_pDevice, &Alloc,
 NULL, (LPD3DXFRAME*)&m_pFrameRoot, &m_pAnimController);


I don't know anything about Direct3D. However, I find it surprising that =
you are passing a pointer to a stack-allocated object (Alloc) where an =
interface pointer is required. It seems reasonable to expect that =
D3DXLoadMeshHierarchyFromXInMemory would want to AddRef this pointer and =
keep it around until such time as the mesh needs to be disposed of. But =
your object will die at the end of the function, regardless of its =
reference count.
--
With best wishes,
    Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not =
necessarily a good idea. It is hard to be sure where they are going to =
land, and it could be dangerous sitting under them as they fly overhead. =
-- RFC 1925

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