Mach-o callback to cfm function

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Jeff Flinn

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Sep 30, 2010, 11:56:58 AM9/30/10
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I'm trying to knit together a legacy Codewarrior CFM application with
XCode Mach-o dll. I've used the approach described by mac support and on
various forums. The approach described uses:

UInt32 gluetab[6] = {0x3D800000, 0x618C0000, 0x800C0000, 0x804C0004,
0x7C0903A6, 0x4E800420};

static void *MachOPtrVoid (void *cfmfp)
{
UInt32 *mfp = (UInt32*) NewPtr( sizeof(gluetab)); // Must later
dispose of allocated memory
mfp[0] = gluetab[0] | ((UInt32)cfmfp >> 16);
mfp[1] = gluetab[1] | ((UInt32)cfmfp & 0xFFFF);
mfp[2] = gluetab[2];
mfp[3] = gluetab[3];
mfp[4] = gluetab[4];
mfp[5] = gluetab[5];
MakeDataExecutable (mfp, sizeof(gluetab));
return( mfp );
}

I'm trying to avoid the heap allocation, and to use a more encapsulated
approach such as:

struct MachOFunctionPointer
{
MachOFunctionPointer(void* cfmProcPtr)
: m0(0x3D800000 | ((UInt32)cfmProcPtr >> 16))
, m1(0x618C0000 | ((UInt32)cfmProcPtr & 0xFFFF))
, m2(0x800C0000)
, m3(0x804C0004)
, m4(0x7C0903A6)
, m5(0x4E800420)
{
MakeDataExecutable(this, sizeof(this));
}

UInt32 m0;
UInt32 m1;
UInt32 m2;
UInt32 m3;
UInt32 m4;
UInt32 m5;
};

constructing an instance on the stack:

MachOFunctionPointer moFncPtr(some_cfm_fnc);

This leads to spurious crashes of the legacy codewarrior app, which I
can't debug because the code warrior debugger won't run on mac intel
machines.

If I pad the above struct at the end to 32 bytes, there are no crashes.
I'm conjecturing that when allocating the former array, that the
allocator is actually allocating to the next power-of-2 size which is 32
bytes. I've tried using CodeWarrior #pragmas to set alignment and
packing, but this doesn't seem to fix the problem.

Any thoughts on this topic are appreciated.

Thanks, Jeff

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