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From: Hui Zhu on 3 Aug 2010 03:50
On Tue, Aug 3, 2010 at 15:37, Eric W. Biederman <ebiederm(a)xmission.com> wrote:
> Hui Zhu <teawater(a)gmail.com> writes:
>
>> Hi,
>>
>> I found that from gdb 7.1 to gdb-cvs-head cannot analyze the core file
>> that get from kdump.
>> What I got:
>> [New <main task>]
>> [New Thread 2719]
>> ../../src/gdb/thread.c:884: internal-error: switch_to_thread:
>> Assertion `inf != NULL' failed.
>> A problem internal to GDB has been detected,
>> further debugging may prove unreliable.
>> Quit this debugging session? (y or n)
>> That is because:
>> �objdump -h ./vmcore
>>
>> ./vmcore: � � file format elf64-x86-64
>>
>> Sections:
>> Idx Name � � � � �Size � � �VMA � � � � � � � LMA � � � � � � � File off �Algn
>> � 0 note0 � � � � 00000a48 �0000000000000000 �0000000000000000 �00000238 �2**0
>> � � � � � � � � � CONTENTS, READONLY
>> � 1 .reg/0 � � � �000000d8 �0000000000000000 �0000000000000000 �000002bc �2**2
>> � � � � � � � � � CONTENTS
>> � 2 .reg � � � � �000000d8 �0000000000000000 �0000000000000000 �000002bc �2**2
>> � � � � � � � � � CONTENTS
>> � 3 .reg/2719 � � 000000d8 �0000000000000000 �0000000000000000 �00000420 �2**2
>> � � � � � � � � � CONTENTS
>> � 4 .reg/0 � � � �000000d8 �0000000000000000 �0000000000000000 �00000584 �2**2
>> � � � � � � � � � CONTENTS
>> � 5 .reg/0 � � � �000000d8 �0000000000000000 �0000000000000000 �000006e8 �2**2
>> � � � � � � � � � CONTENTS
>> Each of reg/n is a cpu core note. �It will be a GDB thread. �n is the
>> prstatus.pr_pid that will be the thread lwpid. �Because the 3 threads
>> pid is same, so GDB get error.
>>
>> current->pid is 0 because this cpu is in idle. �So I add a check, set
>> prstatus.pr_pid to cpu id when current->pid is 0. �Then GDB work OK
>> with the core.
>
> That is a gdb limitation. �It looks to me like applying this patch will
> loose information, and give you no guarantee that prstatus.pr_pid will
> not equal 0.
>
> If you want to change something please do it in a post processing tool.
>
> Eric

Equal 0 is not a bug, the trouble is a lot of core's pid is same.

This is what gdb say:
/* Found an old thread with the same id. It has to be dead,
otherwise we wouldn't be adding a new thread with the same id.
The OS is reusing this id --- delete it, and recreate a new
one. */

Hui

>
>
>> Thanks,
>> Hui
>>
>> Signed-off-by: Hui Zhu <teawater(a)gmail.com>
>> ---
>> �kernel/kexec.c | � �5 ++++-
>> �1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> --- a/kernel/kexec.c
>> +++ b/kernel/kexec.c
>> @@ -1191,7 +1191,10 @@ void crash_save_cpu(struct pt_regs *regs
>> � � � if (!buf)
>> � � � � � � � return;
>> � � � memset(&prstatus, 0, sizeof(prstatus));
>> - � � prstatus.pr_pid = current->pid;
>> + � � if (current->pid)
>> + � � � � � � prstatus.pr_pid = current->pid;
>> + � � else
>> + � � � � � � prstatus.pr_pid = cpu;
>> � � � elf_core_copy_kernel_regs(&prstatus.pr_reg, regs);
>> � � � buf = append_elf_note(buf, KEXEC_CORE_NOTE_NAME, NT_PRSTATUS,
>> � � � � � � � � � � � � � � &prstatus, sizeof(prstatus));
>
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