Re: FYI: SIGBUS with world built by clang

On Thu, 5 Jul 2012 23:11:31 +0300
Konstantin Belousov <kostikbel_at_gmail.com> wrote:

> On Fri, Jul 06, 2012 at 04:15:18AM +0900, Taku YAMAMOTO wrote:
> > On Thu, 5 Jul 2012 00:14:14 +0300
> > Konstantin Belousov <kostikbel_at_gmail.com> wrote:
> > 
> > > On Thu, Jul 05, 2012 at 12:32:01AM +0900, Taku YAMAMOTO wrote:
> > > > On Wed, 04 Jul 2012 17:08:30 +0200
> > > > Dimitry Andric <dim_at_FreeBSD.org> wrote:
> > > > 
> > > > > On 2012-07-04 16:33, Taku YAMAMOTO wrote:
> > > > > > For people having SIGBUS with clang-build world + gcc-build binaries,
> > > > > > 
> > > > > > 
> > > > > > In short words, for any libraries (and never forget about rtld-elf!)
> > > > > > which are potentially called from arbitrary binaries,
> > > > > > compile them with either -mstackrealign or -mstack-alignment=8!
> > > > > > 
> > > > > > The detail is as follows.
> > > > > > 
> > > > > > I've observed that clang carelessly expects the stack being aligned at
> > > > > > 16 byte boundary.
> > > > > 
> > > > > Eh, this is a requirement of the amd64 ABI.  Any compiler that *doesn't*
> > > > > align the stack on 16-byte boundaries is basically broken.  Or are you
> > > > > experiencing this on i386?  Even there, 16-byte alignment would be much
> > > > > better in combination with SSE instructions (which arent' enabled by
> > > > > default, btw).
> > > > 
> > > > Oops, I had to be clear about that!
> > > > Yes, the experiment was took on i386 (actually -march=pentium4).
> > > > 
> > > > > Note that you would get the same issue with newer versions of gcc, which
> > > > > will also assume this alignment.
> > > > 
> > > > Interesting, but the base gcc we currently have won't on i386, I think.
> > > > (I occationally get bitten by similar problem when using -ftree-vectorize)
> > > As far as I understand the rules, $esp % 16 must be zero before call
> > > instruction is executed.
> > 
> > I googled and found that it is enforced by MacOS X ABI for IA32 but
> > i386 SysV ABI defines otherwise (8 bytes instead of 16 bytes).
> No, SysV ABI only requires 4-byte alignment for the stack on i386.
(snip)

Oh, I stand corrected.
Thank you :)

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