[vorbis-dev] segfault cause found

[Monty]

> Problem solved! (Or rather, worked around...)  The problem with the segfault 
> appears to have indeed been with alloca.  There is a function _alloca in 
> libgcc.a that comes with the mingw32 distribution of gcc-2.95.2.  After 
> examining the generated assembly code from envelope.c (and others), I found 
> that when I left the #define alloca(x) (_alloca(x)) in os.h, it would link 
> to this function.  If you #ifdef the define out, it would simply subtract 
> the required number of bytes off of the stack pointer.  I haven't had a 
> chance to look at what the _alloca() function is doing in mingw32, but 
> removing the #define does the trick.

Ah.  MSVC requires _alloca() as a synonym for *NIX alloca().  This must be an 
internal function in mingw32 that I shouldn't use.

The obvious fault is me using #ifdef _WIN32 in os.h.  Is, perhaps, _MSVC_ or
somethign like that a better idea?

> #ifndef alloca
> #if defined(_WIN32) && !defined(__GNUC__)
> #define alloca(x) (_alloca(x))
> #endif
> #endif

Since we're trying to fix it right, it seems like that could trip us up
eventually too... what do other developers who code for both WIN32/GNU and
their unholy union do?

Monty

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