Re: PATCH [i386 windows targets]: Disallow regparm for functions that probe stack

[Christopher Faylor <cgf at redhat dot com>]

On Sun, Oct 12, 2003 at 07:32:14PM -0400, Christopher Faylor wrote:
>On Mon, Oct 13, 2003 at 07:29:12AM +1000, Danny Smith wrote:
>>Hello, this fixes a bug on win32 targets that is related to PR 12209.
>>
>>The stack probing code (i386/cygwin.asm) that is emitted when a function
>>requests allocation of more than CHECK_STACK_LIMIT bytes on the stack
>>overwrites EAX register.  This causes functions with regparm attribute
>>to return nonsense results, without warning.  eg:
>
>Hmm.  I could have sworn that this was fixed once already in a different
>way.
>
>I'll have to do some email archaelogy.

I couldn't find any email about this but I do recall researching what
needed to be done to fix it.

It seems like it should be possible to detect the case where EAX is
live, push it on the stack, and "pop" it after calling __chkstk/alloca.
It won't be a true, "pop" of course because the stack will have been
adjusted but it should still be possible to retrieve the register,
regardless.

I'll look into doing this but it will require some digging on my part.
If anyone has a suggestion to point me in the right direction, I'd
appreciate it.

cgf