[squeak-dev] x86 linux VM FFI FPU stack overflow

nicolas cellier ncellier at ifrance.com
Sun Jan 11 11:22:09 UTC 2009

Apologies for the cryptic subject...

I have some news about http://bugs.squeak.org/view.php?id=3929
I detected with gdb that the example I provided triggers a FPU stack 
overflow. When this occurs, a qNan is placed on FPU stack top.

Thus, though ffiFloatReturnValue == 0.0, testing in Smalltalk (self 
myFFICall = 0.0) will result in 0.0==Nan due to stack overflow.
primitive which execute special send #= will incorrectly return false...

Don't tell me to not use = on Floats, this is not the problem, you can 
replace the test with (self myFFICall < 1.0), you will get (0.0<qNan) -> 
false all the same.

At this point, I see two possibilities:
- either I totally messed up with calling conventions
- or the FFI glue ffiCallAddressOf is broken

I have no knowledge about IA-32 and don't wish to learn further, using 
gdb at instruction level was already painfull enough for me.
Can somebody aware of x86 and calling convention check my guess?


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