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Next: kexec: set prstatus.pr_pid to cpu id when current->pid is 0
From: Eric W. Biederman on 3 Aug 2010 03:40
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


> 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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