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Re: [Bug target/53383] Allow -mpreferred-stack-boundary=3 on x86-64
- From: Jan Hubicka <hubicka at ucw dot cz>
- To: hubicka at ucw dot cz <gcc-bugzilla at gcc dot gnu dot org>
- Cc: gcc-bugs at gcc dot gnu dot org
- Date: Sun, 20 May 2012 13:34:08 +0200
- Subject: Re: [Bug target/53383] Allow -mpreferred-stack-boundary=3 on x86-64
- References: <bug-53383-4@http.gcc.gnu.org/bugzilla/> <bug-53383-4-GE5ei6XIp2@http.gcc.gnu.org/bugzilla/>
> > This isn't necessary. If __int128 is put on stack by caller,
> > the stack must be aligned at 16 bytes.
>
> Not when you call function with -fpreferred-stack-boundary=3
> and it is itself compiled with -fpreferred-stack-boudnary=4
> and calls another functions passing __int128.
> Thus the ABI incompatibility.
... and the alignment code is there not to align stack frame, but to
align the __int128bit position within the argument area. The
va_arg calls beforehand are of unknon count.
> Honza