From: "Ulrich Weigand" <uweigand@de.ibm.com>
To: n.sherlock@gmail.com (Nicholas Sherlock)
Cc: gdb@sourceware.org
Subject: Re: ARM EABI Linux, breakpoints cause SIGILL and target dies
Date: Fri, 20 Jan 2012 10:45:00 -0000 [thread overview]
Message-ID: <201201201044.q0KAimIE006755@d06av02.portsmouth.uk.ibm.com> (raw)
In-Reply-To: <CADwwazYxTvu4Qf=a+x2Ot4nXBuJNxOCdKw7mZcNHtgCZLtUZzw@mail.gmail.com> from "Nicholas Sherlock" at Jan 20, 2012 03:45:11 PM
Nicholas Sherlock wrote:
> Running a.out alone or with GDB works fine, but any operation that
> causes GDB to set a breakpoint results in the target being killed by
> SIGILL:
[snip]
> So I would expect that this would work. Another piece of the puzzle, I
> have a different phone here running a different Linux kernel, but the
> same Ubuntu usermode binaries, where GDB breakpoints work perfectly:
[snip]
> How do I begin to debug this problem? I have the source code available
> for both kernels if there is something to investigate there.
So there's two issues here:
- The kernel is supposed to recognize the special undefined instructions
use to implement breakpoints, and deliver SIGTRAP instead of SIGILL if
execution hits one of those. It may be that the older of the two kernels
does not properly handle this, in particular for Thumb-2 breakpoints
which were added only recently.
If you have the kernel sources, you might want to compare the routines
installed via register_undef_hook in arch/arm/kernel/ptrace.c.
- Even on old kernels that return SIGILL, there is apparently some code
in GDB that tries to recognize breakpoints anyway. It may well be
that this code does not (any longer) work correctly; it is never
exercised on recent kernels, so a bug might have crept in ...
Can you do a run with "set debug infrun 1" in the case where you
get the SIGILL?
Bye,
Ulrich
--
Dr. Ulrich Weigand
GNU Toolchain for Linux on System z and Cell BE
Ulrich.Weigand@de.ibm.com
next prev parent reply other threads:[~2012-01-20 10:45 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CADwwazYuWuicgqL=4JyxbdoN+6MmVg354bD6UTzC=Ew-po8JzA@mail.gmail.com>
2012-01-20 2:45 ` Nicholas Sherlock
2012-01-20 10:45 ` Ulrich Weigand [this message]
2012-01-22 23:34 ` Nicholas Sherlock
2012-01-23 1:29 ` Nicholas Sherlock
2012-01-23 13:29 ` Ulrich Weigand
2012-01-24 2:44 ` Nicholas Sherlock
2012-01-24 3:02 ` Nicholas Sherlock
2012-01-24 13:37 ` Ulrich Weigand
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