Converting Visual C/C++ inline assembly code to GCC equivalent code

Question

I have found the following function here and would like to get it to compile under MinGW:

size_t stackavail()
{
    static unsigned StackPtr;
    __asm mov [StackPtr],esp
    static MEMORY_BASIC_INFORMATION mbi;
    VirtualQuery((PVOID)StackPtr,&mbi,sizeof(mbi));
    return StackPtr-(unsigned)mbi.AllocationBase;
}

I tried to modify the code above and managed to compile and run it:

size_t stackavail()
{
    static unsigned StackPtr;

    __asm__ ("movl %%esp, %0\n\t" : "=r" (StackPtr) );
    MEMORY_BASIC_INFORMATION mbi;
    VirtualQuery((PVOID)StackPtr, &mbi, sizeof(mbi));
    return StackPtr-(unsigned)mbi.AllocationBase;
}

But I'm in doubt. Is it correct? Is there another way to do it?

Looks correct for me, but you should try to avoid using `__asm__` for code that is intended to be portable. — πάντα ῥεῖ, Jan 21 '14 at 19:06
Also, use of a static local makes this terribly unthreadsafe. — Ben Voigt, Jan 21 '14 at 20:26
How about using the GCC builtin [`__builtin_frame_address()`](http://gcc.gnu.org/onlinedocs/gcc/Return-Address.html) instead of inline assembly? That's even portable to other architectures (such as x86-64). — Adam Rosenfield, Jan 21 '14 at 20:33
Thank you all for the help! @AdamRosenfield: Great tip. It works fine. — Fabiano Freitas, Jan 27 '14 at 18:39

score 0 · Accepted Answer · answered Jan 21 '14 at 20:25

0

You can get rid of the inline ASM, use

void* StackPtr = &StackPtr;

answered Jan 21 '14 at 20:25

Ben Voigt

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Converting Visual C/C++ inline assembly code to GCC equivalent code

1 Answers1