linux-kernel - getting false SIGTRAP breakpoints in kernel i.e. kernel hung unless gdb remotely attached on x86 & cont is issued

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Message-ID: <48D10A70.8050202@option.com>
Date:	Wed, 17 Sep 2008 15:47:28 +0200
From:	Denis Joseph Barrow <D.Barow@...ion.com>
To:	"Amit S. Kale" <amitkale@...syssoft.com>,
	Tom Rini <trini@...nel.crashing.org>,
	Jason Wessel <jason.wessel@...driver.com>,
	David Grothe <dave@...m.com>, Tigran Aivazian <tigran@....com>,
	linux-kernel@...r.kernel.org
Subject: getting false SIGTRAP breakpoints in kernel i.e. kernel hung unless
 gdb remotely attached on x86 & cont is issued

Hi ladies/gentlemen,
The kernel I'm running gdb with is 2.6.27-rc4
The false sigtrap is occuring in ia32_sysenter_target in arch/x86/kernel/entry_32.S:303
when gdb is stepped from the user process as described below

To reproduce
compile kernel with kgdb support 
compile my randsleep program attached using the .mk script
as root
attach randsleep to an idle serial port e.g. /dev/ttyS0 by typing
randsleep /dev/ttyS0
from another bash shell type
ps -aux | grep randsleep

gdb ./randsleep
attach <pid of randsleep>

You should get messages from gdb like
Attaching to program: /home/djbarrow/devel2/randsleep/randsleep, process 6397
Reading symbols from /lib/tls/i686/cmov/libc.so.6...done.
Loaded symbols for /lib/tls/i686/cmov/libc.so.6
Reading symbols from /lib/ld-linux.so.2...done.
Loaded symbols for /lib/ld-linux.so.2
0xb7fda430 in __kernel_vsyscall ()

Now type step.

The machine is now hung until gdb attaches remotely.

-- 
best regards,
D.J. Barrow

View attachment "randsleep.c" of type "text/x-csrc" (1647 bytes)

View attachment "mk" of type "text/plain" (31 bytes)