Re: ddb(4) spoils kernel stack in CURRENT?

I worried that gdb probably had workaround for the large stack argument.
I'll have to dig it up, thanks for the heads up.

  -Kip

On 12/20/06, Dmitry Pryanishnikov <dmitry_at_atlantis.dp.ua> wrote:
>
>
> Hello!
>
> On Wed, 20 Dec 2006, Kostik Belousov wrote:
> >>> So it looks like a regression in CURRENT vs RELENG_6 (either ddb
> 'spoils'
> >>> the stack somehow, or kgdb fails to unwind it).
> >
> > Could you further localize the problem, i.e. try to backtrace CURRENT
> dump
>
>    Good news: I've managed to localize the bug! I'm Feeling Lucky (TM) ;)
> just because CURRENT on my notebook was updated approx. at 17-Dec 00:00,
> and it didn't manifest such a behaviour! So it was easy to identify the
> regression - it comes with the following commit:
>
> -----------------------------------------------------------------------
>
> Date: Sun, 17 Dec 2006 05:07:01 +0000 (UTC)
> From: Kip Macy <kmacy_at_freebsd.org>
> To: src-committers_at_freebsd.org, cvs-src_at_freebsd.org, cvs-all_at_freebsd.org
> Subject: cvs commit: src/sys/i386/i386 apic_vector.s exception.slocal_apic.c
>           trap.c vm86.c vm86bios.s src/sys/i386/include apicvar.h
>           src/sys/i386/isa atpic.c atpic_vector.s icu.h
>
> kmacy       2006-12-17 05:07:01 UTC
>
>    FreeBSD src repository
>
>    Modified files:
>      sys/i386/i386        apic_vector.s exception.s local_apic.c
>                           trap.c vm86.c vm86bios.s
>      sys/i386/include     apicvar.h
>      sys/i386/isa         atpic.c atpic_vector.s icu.h
>    Log:
>    Evidently FreeBSD has long relied on the compiler to treat structures
>    passed by value (trap frames) as if they were in fact being passed by
>    reference. For better or worse, this incorrect behaviour is no longer
>    present in gcc 4.1. In this patch I convert all trapframe arguments to
>    be explicitly pass by reference. I also remove vm86_initflags, pushing
>    the very little work that it actually does up into vm86_prepcall.
>
> -----------------------------------------------------------------------
>
> So kernel built from sources as of date=2006.12.17.05.00.00 gives dump
> with analyzable backtrace, and kernel built from sources as of
> date=2006.12.17.05.10.00 (which include this commit) gives dump
> which confuses kgdb. I believe that commit itself is correct,
> but kgdb contains some workaround against the old (incorrect) behaviour
> of the kernel, so it's the kgdb that should be fixed.
>
> Sincerely, Dmitry
> --
> Atlantis ISP, System Administrator
> e-mail:  dmitry_at_atlantis.dp.ua
> nic-hdl: LYNX-RIPE
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