FYI: SIGBUS with world built by clang

[Taku YAMAMOTO]

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).

> i386 csu explicitely aligns the stack before calling into C land, everything
> else should be the C compiler own offence :).

Unfortunately it is difficult when we have to deal with binaries produced by
random compilers, such as Win32 app via wine, mplayer with win32-codecs, etc. ;)

JITs, like Java and mono, also have possibility to become victims if they
emit native codes without paying attention to the stack alignment, though
I'm not sure.

Just my random thoughts,
-- 
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 | __ <     <taku at tackymt.homeip.net>

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