Re: SSE vs. stack alignment vs. pthread

From: Daniel Eischen (deischen_at_freebsd.org)
Date: 11/24/04

  • Next message: Craig Boston: "Re: SSE vs. stack alignment vs. pthread" 
    Date: Wed, 24 Nov 2004 02:36:55 -0500 (EST)
To: Craig Boston <craig@tobuj.gank.org>

    On Wed, 24 Nov 2004, Craig Boston wrote:

    > First of all, I'd like to apologize for cross-posting to -hackers and
    > -threads. I'm not sure yet if this is an application bug, a gcc
    > bug, or a pthreads bug, so here goes...
    >
    > I'm currently working on the audacity port. It's up to 1.2.3, but I
    > want to get a problem I've observed with 1.2.2 resolved to make sure
    > that it doesn't crop up later or affect other software...
    >
    > Long story short, audacity is a threaded program. A straight compile of
    > 1.2.2 results in a 100% reproducible bus error that happens on multiple
    > Pentium-4 machines (5.3-STABLE). It always happens at this instruction:
    >
    > 0x081807c4: movaps %xmm0,0xffffff68(%ebp)
    >
    > Now, at that time ebp is 0xbfadc6c0, so ebp+0xffffff68 (-0x152) is 0xbfadc56e.
    > Oops, that's not 16-byte aligned like SSE wants. The offsets vary sligthly
    > depending on the compile flags, etc., but the result is always the same --
    > SIGBUS.

    Tor Egge reported similar problem to me yesterday. I haven't had a chance
    to test his patch, but this supposedly fixes it.

    Index: lib/libc/i386/gen/makecontext.c
    ===================================================================
    RCS file: /home/ncvs/src/lib/libc/i386/gen/makecontext.c,v
    retrieving revision 1.4
    diff -u -r1.4 makecontext.c
    --- lib/libc/i386/gen/makecontext.c 2 Jul 2004 14:19:44 -0000 1.4
    +++ lib/libc/i386/gen/makecontext.c 22 Nov 2004 22:51:49 -0000
    @@ -118,7 +118,9 @@
                      * address, _ctx_start, and ucp) and argc arguments.
                      * We allow the arguments to be pointers also.
                      */
    - stack_top = stack_top - (sizeof(intptr_t) * (3 + argc));
    + stack_top = stack_top - (sizeof(intptr_t) * (1 + argc));
    + stack_top -= ((long) stack_top & 15); /* 16 bytes alignment */
    + stack_top -= sizeof(intptr_t) * 2;
                     argp = (intptr_t *)stack_top;

                     /*

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