Simplest way to remove something from the FPU stack

assembly x86 x87
Mason Wheeler picture Mason Wheeler · Jan 23, 2011 · Viewed 7.3k times · Source

I've been having some trouble lately with FPU stack overflows. I managed to track it back to a buggy library function that pushes a garbage value onto the FPU stack every time it's called and never cleans it up.

Fortunately, this is easily reproducible and I know exactly what conditions cause it. I can drop a block of inline ASM into the routine that calls this routine to pop the top value back off the FPU stack... except I don't quite know what to write. My ASM-fu is fair to middlin', but not that strong.

So what's the simplest way to get rid of the top value on the FPU stack in x86 assembly, assuming it's garbage data and I don't care about the value?

Answer

PhiS picture PhiS · Jan 26, 2011

For Delphi/BASM, in my view the simplest way to pop the FPU stack once is:

asm
 fstp st(0)
end;

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