Date: Thu, 13 Jan 2011 19:06:25 +0000 From: Alexander Best <arundel@freebsd.org> To: Ryan Stone <rysto32@gmail.com> Cc: FreeBSD Hackers <hackers@freebsd.org> Subject: Re: What does the FreeBSD/i386 ABI say about stack alignment? Message-ID: <20110113190625.GA76352@freebsd.org> In-Reply-To: <AANLkTikrsHUO3M%2Bfvo0kO%2B3dPq8OHu5L2zBf3fa3jL2x@mail.gmail.com> References: <AANLkTikrsHUO3M%2Bfvo0kO%2B3dPq8OHu5L2zBf3fa3jL2x@mail.gmail.com>
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On Thu Jan 13 11, Ryan Stone wrote: > I've been trying to get an application compiled with gcc 4.5.1 running > on FreeBSD 8.1, but it's been crashing during startup with a SIGBUS. > It turns out that the problem is that gcc is issuing SSE > instructions(in my case, a movdqa) that assume that the stack will be > aligned to a 16-byte boundary. It seems that Linux/i386 guarantees > this, and I worry that gcc has extended this assumption to all i386 > architectures. I'm assuming that FreeBSD doesn't make any such > promises based on the fact that I'm getting crashes. > > There does seem to be a flag (-mstackrealign) that you can set to > force gcc to align the stack to what it wants, but that pessimizes the > generated code a bit. Some googling would seem to indicate that > -mpreferred-stack-boundary won't always handle this problem correctly. > > Any ideas? My inclination, at least for our local source tree here at > $WORK, would be to accommodate gcc and guarantee the stack alignment > that it wants rather than pessimize our application. It seems we have > an old local patch/hack in our FreeBSD 6.1 tree(apparently based on > this: http://www.freebsd.org/cgi/getmsg.cgi?fetch=438552+0+/usr/local/www/db/text/2000/freebsd-current/20000507.freebsd-current). > I believe that this patch is the reason why we haven't seen the > problem when running on 6.1, but the patch doesn't seem to work > anymore on 8.1. i'm experiencing a similar issue on amd64 with mplayer (svn snapshot) and gcc46: otaku% ./mplayer ~/filme/wiedhow.mkv MPlayer SVN-r32787-4.6.0 (C) 2000-2011 MPlayer Team 161 audio & 350 video codecs Playing /home/arundel/filme/wiedhow.mkv. zsh: illegal hardware instruction (core dumped) ./mplayer ~/filme/wiedhow.mkv otaku% echo $? 132 i'm not sure however, if both matters are related. gdb and 'bt' report: #0 0x0000000805327f03 in sscanf (str=0xa <Address 0xa out of bounds>, fmt=0x7fffffbffe60 <Address 0x7fffffbffe60 out of bounds>) at /usr/subversion-src/lib/libc/stdio/sscanf.c:46 46 { [New Thread 80a407400 (LWP 105253/initial thread)] (gdb) bt #0 0x0000000805327f03 in sscanf (str=0xa <Address 0xa out of bounds>, fmt=0x7fffffbffe60 <Address 0x7fffffbffe60 out of bounds>) at /usr/subversion-src/lib/libc/stdio/sscanf.c:46 #1 0x000000000062fa25 in vsscanf () #2 0x0000000805327f84 in sscanf (str=Variable "str" is not available. ) at /usr/subversion-src/lib/libc/stdio/sscanf.c:51 #3 0x000000000062fa25 in vsscanf () cheers. alex -- a13x
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