Date: Fri, 6 Jul 2012 04:15:18 +0900 From: Taku YAMAMOTO <taku@tackymt.homeip.net> To: Konstantin Belousov <kostikbel@gmail.com> Cc: freebsd-current@freebsd.org Subject: Re: FYI: SIGBUS with world built by clang Message-ID: <20120706041518.de7e2ab5.taku@tackymt.homeip.net> In-Reply-To: <20120704211414.GR2337@deviant.kiev.zoral.com.ua> References: <20120704233316.70ec8654.taku@tackymt.homeip.net> <4FF45C6E.1080000@FreeBSD.org> <20120705003201.bb297e8a.taku@tackymt.homeip.net> <20120704211414.GR2337@deviant.kiev.zoral.com.ua>
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On Thu, 5 Jul 2012 00:14:14 +0300
Konstantin Belousov <kostikbel@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@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,
--
-|-__ YAMAMOTO, Taku
| __ < <taku@tackymt.homeip.net>
- A chicken is an egg's way of producing more eggs. -
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