Date: Sat, 06 Dec 2003 17:16:00 -0800 From: Peter Wemm <peter@wemm.org> To: Daniel Eischen <eischen@vigrid.com> Cc: cvs-all@FreeBSD.org Subject: Re: cvs commit: src/lib/libc/amd64/gen makecontext.c Message-ID: <20031207011600.E70C32A7EA@canning.wemm.org> In-Reply-To: <Pine.GSO.4.10.10312042042001.1477-100000@pcnet5.pcnet.com>
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Daniel Eischen wrote:
> On Thu, 4 Dec 2003, Peter Wemm wrote:
>
> > peter 2003/12/04 17:36:44 PST
> >
> > FreeBSD src repository
> >
> > Modified files:
> > lib/libc/amd64/gen makecontext.c
> > Log:
> > "Fix" makecontext() so that the C code begins execution with its
> > ABI-required stack alignment. C code expects that the push of the
> > return address disturbed the 16 byte alignment and it will take correctiv
e
> > measures to fix it before making another call. Of course, if its wrong
> > to start with, then all hell breaks loose. Essentially we "fix" this
> > by making the stack alignment odd to start with.
>
> Hey, you didn't include this little bit of knowledge in your amd64 "notes"
> that you sent me ;-)
Heh. I never get it right. I've had to resort to things like this:
assert((((long)__builtin_frame_address(0)) & 15 == 0), "misaligned stack!");
The trick of course is that gcc-3.3.3 is broken and __builtin_frame_address(0)
doesn't actually work unless you compile *also* with -fno-omit-frame-pointer
on amd64.
Anyway, thats the only way I've ever been able to get this stuff sorted out. :-)
Cheers,
-Peter
--
Peter Wemm - peter@wemm.org; peter@FreeBSD.org; peter@yahoo-inc.com
"All of this is for nothing if we don't go to the stars" - JMS/B5
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