Date: Thu, 5 Jul 2012 23:11:31 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Taku YAMAMOTO <taku@tackymt.homeip.net> Cc: freebsd-current@freebsd.org Subject: Re: FYI: SIGBUS with world built by clang Message-ID: <20120705201131.GC2338@deviant.kiev.zoral.com.ua> In-Reply-To: <20120706041518.de7e2ab5.taku@tackymt.homeip.net> References: <20120704233316.70ec8654.taku@tackymt.homeip.net> <4FF45C6E.1080000@FreeBSD.org> <20120705003201.bb297e8a.taku@tackymt.homeip.net> <20120704211414.GR2337@deviant.kiev.zoral.com.ua> <20120706041518.de7e2ab5.taku@tackymt.homeip.net>
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[-- Attachment #1 --] 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@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). No, SysV ABI only requires 4-byte alignment for the stack on i386. > > > 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. - [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (FreeBSD) iEYEARECAAYFAk/19PMACgkQC3+MBN1Mb4iEcACg718pKmwEUvCLhSqe7K3c7sFI 5lQAoLl5BwSokpjEHdm4FOmiomJ/lph/ =c8qA -----END PGP SIGNATURE-----help
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