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

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Date:	Wed, 17 Sep 2008 17:40:34 +0200
From:	Denis Joseph Barrow <D.Barow@...ion.com>
To:	Jason Wessel <jason.wessel@...driver.com>
CC:	"Amit S. Kale" <amitkale@...syssoft.com>,
	Tom Rini <trini@...nel.crashing.org>,
	David Grothe <dave@...m.com>, linux-kernel@...r.kernel.org
Subject: Re: getting false SIGTRAP breakpoints in kernel i.e. kernel hung
 unless gdb remotely attached on x86 & cont is issued

Hi Jason,
Just to be complete the kernel config might be useful in reproducing the bug.
I'm running Ubuntu 8.04 - the Hardy Heron - released in April 2008.
				
Jason Wessel wrote:
> Denis Joseph Barrow wrote:
>> 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
>>
>>   
> 
> Your example does not indicate how or why you setup kgdb.  kgdb can be
> compiled into the kernel, but it should not have any effect what so ever
> unless it is configured for use because it will not register to receive
> any of the breakpoint or single stepping traps.
> 
> Perhaps there is more to the description of your problem?
> 
> Jason.
> 
>> 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 "config-2.6.27-rc4" of type "text/plain" (89014 bytes)