[Crash-utility] [PATCH v3 2/2] arm/arm64: read elf notes for qemu generated cores
Dave Anderson
anderson at redhat.com
Fri Nov 20 19:31:37 UTC 2015
----- Original Message -----
> QEMU can generate both non-makedumpfile (just elf) and makedumpfile
> formatted kdumps. In neither case will crash_notes have prstatus, as
> crash_kexec doesn't run in the kernel, however the elf notes will
> contain the prstatus, and we can dig them out of there.
I don't have a lot of ARM and ARM64 dumpfiles, but just doing a
quick sanity test of your patch, I came across this ARM dumpfile,
which I believe may be a QEMU-generated ELF vmcore. I'm not sure,
but it only has 1 NT_PRSTATUS note for the 1 online cpu (of 5 cpus).
But anyway, note that as expected, it cannot find the registers in the
kernel's uninitialized crash_notes -- here without your patch:
$ crash vmcore.pae vmlinux.pae.gz
crash 7.1.4rc15
Copyright (C) 2002-2014 Red Hat, Inc.
Copyright (C) 2004, 2005, 2006, 2010 IBM Corporation
Copyright (C) 1999-2006 Hewlett-Packard Co
Copyright (C) 2005, 2006, 2011, 2012 Fujitsu Limited
Copyright (C) 2006, 2007 VA Linux Systems Japan K.K.
Copyright (C) 2005, 2011 NEC Corporation
Copyright (C) 1999, 2002, 2007 Silicon Graphics, Inc.
Copyright (C) 1999, 2000, 2001, 2002 Mission Critical Linux, Inc.
This program is free software, covered by the GNU General Public License,
and you are welcome to change it and/or distribute copies of it under
certain conditions. Enter "help copying" to see the conditions.
This program has absolutely no warranty. Enter "help warranty" for details.
GNU gdb (GDB) 7.6
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "--host=x86_64-unknown-linux-gnu --target=arm-elf-linux"...
WARNING: invalid note (n_type != NT_PRSTATUS)
WARNING: cannot retrieve registers for active tasks
KERNEL: vmlinux.pae.gz
DUMPFILE: vmcore.pae
CPUS: 5 [OFFLINE: 4]
DATE: Sun Jun 8 18:27:39 2014
UPTIME: 00:03:22
LOAD AVERAGE: 0.16, 0.16, 0.07
TASKS: 51
NODENAME: buildroot
RELEASE: 3.13.5
VERSION: #3 SMP Mon Jun 9 05:58:39 CST 2014
MACHINE: armv7l (unknown Mhz)
MEMORY: 256 MB
PANIC: "SysRq : Trigger a crash"
PID: 732
COMMAND: "sh"
TASK: 8bcead00 [THREAD_INFO: 8ad32000]
CPU: 0
STATE: TASK_RUNNING (SYSRQ)
crash> bt -a
PID: 732 TASK: 8bcead00 CPU: 0 COMMAND: "sh"
bt: WARNING: cannot determine starting stack frame for task 8bcead00
PID: 0 TASK: 8bc561c0 CPU: 1 COMMAND: "swapper/1"
bt: WARNING: cannot determine starting stack frame for task 8bc561c0
PID: 0 TASK: 8bc56580 CPU: 2 COMMAND: "swapper/2"
bt: WARNING: cannot determine starting stack frame for task 8bc56580
PID: 0 TASK: 8bc56940 CPU: 3 COMMAND: "swapper/3"
bt: WARNING: cannot determine starting stack frame for task 8bc56940
PID: 0 TASK: 8bc56d00 CPU: 4 COMMAND: "swapper/4"
bt: WARNING: cannot determine starting stack frame for task 8bc56d00
crash>
With your patch applied, it generates a SIGSEGV in arm_get_crash_notes():
$ ./crash /usr/dumps/ARM/vmcore.pae /usr/dumps/ARM/vmlinux.pae.gz
crash 7.1.4rc15
Copyright (C) 2002-2014 Red Hat, Inc.
Copyright (C) 2004, 2005, 2006, 2010 IBM Corporation
Copyright (C) 1999-2006 Hewlett-Packard Co
Copyright (C) 2005, 2006, 2011, 2012 Fujitsu Limited
Copyright (C) 2006, 2007 VA Linux Systems Japan K.K.
Copyright (C) 2005, 2011 NEC Corporation
Copyright (C) 1999, 2002, 2007 Silicon Graphics, Inc.
Copyright (C) 1999, 2000, 2001, 2002 Mission Critical Linux, Inc.
This program is free software, covered by the GNU General Public License,
and you are welcome to change it and/or distribute copies of it under
certain conditions. Enter "help copying" to see the conditions.
This program has absolutely no warranty. Enter "help warranty" for details.
GNU gdb (GDB) 7.6
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "--host=x86_64-unknown-linux-gnu --target=arm-elf-linux"...
Segmentation fault (core dumped)
$
I haven't debugged it other than determining that the "note" it looks to
have found the single note OK, but then upon continuation the next time
through the loop, the "note" pointer is valid at line 597, but your
function sets it back to NULL, and therefore it craps out at line 622:
597 note = (Elf32_Nhdr *)buf;
598 p = buf + sizeof(Elf32_Nhdr);
599
600 /*
601 * dumpfiles created with qemu won't have crash_notes, but there will
602 * be elf notes.
603 */
604 if (note->n_namesz == 0 && (DISKDUMP_DUMPFILE() || KDUMP_DUMPFILE())) {
605 if (DISKDUMP_DUMPFILE())
606 note = diskdump_get_prstatus_percpu(i);
607 else if (KDUMP_DUMPFILE())
608 note = netdump_get_prstatus_percpu(i);
609 if (note) {
610 /*
611 * SIZE(note_buf) accounts for a "final note", which is a
612 * trailing empty elf note header.
613 */
614 long notesz = SIZE(note_buf) - sizeof(Elf32_Nhdr);
615
616 if (sizeof(Elf32_Nhdr) + roundup(note->n_namesz, 4) +
617 note->n_descsz == notesz)
618 BCOPY((char *)note, buf, notesz);
619 }
620 }
621
622 if (note->n_type != NT_PRSTATUS) {
623 error(WARNING, "invalid note (n_type != NT_PRSTATUS)\n");
624 goto fail;
625 }
Not sure how you want to handle that, probably just bail out the same way
if note becomes NULL?
Dave
> ---
> arm.c | 22 ++++++++++++++++++++++
> arm64.c | 22 ++++++++++++++++++++++
> defs.h | 1 +
> netdump.c | 21 +++++++++++++++++++++
> 4 files changed, 66 insertions(+)
>
> diff --git a/arm.c b/arm.c
> index ffc7c06d0f42c..8fc3d48a8ac89 100644
> --- a/arm.c
> +++ b/arm.c
> @@ -597,6 +597,28 @@ arm_get_crash_notes(void)
> note = (Elf32_Nhdr *)buf;
> p = buf + sizeof(Elf32_Nhdr);
>
> + /*
> + * dumpfiles created with qemu won't have crash_notes, but there will
> + * be elf notes.
> + */
> + if (note->n_namesz == 0 && (DISKDUMP_DUMPFILE() || KDUMP_DUMPFILE())) {
> + if (DISKDUMP_DUMPFILE())
> + note = diskdump_get_prstatus_percpu(i);
> + else if (KDUMP_DUMPFILE())
> + note = netdump_get_prstatus_percpu(i);
> + if (note) {
> + /*
> + * SIZE(note_buf) accounts for a "final note", which is a
> + * trailing empty elf note header.
> + */
> + long notesz = SIZE(note_buf) - sizeof(Elf32_Nhdr);
> +
> + if (sizeof(Elf32_Nhdr) + roundup(note->n_namesz, 4) +
> + note->n_descsz == notesz)
> + BCOPY((char *)note, buf, notesz);
> + }
> + }
> +
> if (note->n_type != NT_PRSTATUS) {
> error(WARNING, "invalid note (n_type != NT_PRSTATUS)\n");
> goto fail;
> diff --git a/arm64.c b/arm64.c
> index 9d03d1d54b574..b399d7a5c37fe 100644
> --- a/arm64.c
> +++ b/arm64.c
> @@ -1827,6 +1827,28 @@ arm64_get_crash_notes(void)
> note = (Elf64_Nhdr *)buf;
> p = buf + sizeof(Elf64_Nhdr);
>
> + /*
> + * dumpfiles created with qemu won't have crash_notes, but there will
> + * be elf notes.
> + */
> + if (note->n_namesz == 0 && (DISKDUMP_DUMPFILE() || KDUMP_DUMPFILE())) {
> + if (DISKDUMP_DUMPFILE())
> + note = diskdump_get_prstatus_percpu(i);
> + else if (KDUMP_DUMPFILE())
> + note = netdump_get_prstatus_percpu(i);
> + if (note) {
> + /*
> + * SIZE(note_buf) accounts for a "final note", which is a
> + * trailing empty elf note header.
> + */
> + long notesz = SIZE(note_buf) - sizeof(Elf64_Nhdr);
> +
> + if (sizeof(Elf64_Nhdr) + roundup(note->n_namesz, 4) +
> + note->n_descsz == notesz)
> + BCOPY((char *)note, buf, notesz);
> + }
> + }
> +
> if (note->n_type != NT_PRSTATUS) {
> error(WARNING, "invalid note (n_type != NT_PRSTATUS)\n");
> goto fail;
> diff --git a/defs.h b/defs.h
> index 3e5dbd99942b2..8a4045ec78c37 100644
> --- a/defs.h
> +++ b/defs.h
> @@ -5720,6 +5720,7 @@ void dump_registers_for_qemu_mem_dump(void);
> void kdump_backup_region_init(void);
> void display_regs_from_elf_notes(int, FILE *);
> void display_ELF_note(int, int, void *, FILE *);
> +void *netdump_get_prstatus_percpu(int);
> #define PRSTATUS_NOTE (1)
> #define QEMU_NOTE (2)
>
> diff --git a/netdump.c b/netdump.c
> index bfa818fdef8e1..3ff49f0577c23 100644
> --- a/netdump.c
> +++ b/netdump.c
> @@ -2345,6 +2345,27 @@ dump_Elf64_Nhdr(Elf64_Off offset, int store)
> return len;
> }
>
> +void *
> +netdump_get_prstatus_percpu(int cpu)
> +{
> + int online;
> +
> + if ((cpu < 0) || (cpu >= nd->num_prstatus_notes))
> + return NULL;
> +
> + /*
> + * If no cpu mapping was done, then there must be
> + * a one-to-one relationship between the number
> + * of online cpus and the number of notes.
> + */
> + if ((online = get_cpus_online()) &&
> + (online == kt->cpus) &&
> + (online != nd->num_prstatus_notes))
> + return NULL;
> +
> + return nd->nt_prstatus_percpu[cpu];
> +}
> +
> /*
> * Send the request to the proper architecture hander.
> */
> --
> 2.4.3
>
>
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