3:33 p.m.
I am trying to use gcore to generate a user application core from a kernel dump file. I
compiled the latest crash-7.1.6 and crash-gcore-command-1.3.1 from
https://people.redhat.com/anderson/. I installed a debug kernel
(vmlinux-4.1.34-33-debug.gz from openSUSE Leap 42.1) and did a controlled (sysrq-trigger)
crash. When I attempt to use gcore on the process in question, after reading
<https://people.redhat.com/anderson/extensions/gcore_help_gcore.html>;, I get a
segmentation fault:
eje-code:~ # crash /boot/vmlinux-4.1.34-33-debug.gz
/var/crash/2016-10-31-17\:01//vmcore
crash 7.1.6
Copyright (C) 2002-2016 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 "x86_64-unknown-linux-gnu"...
KERNEL: /boot/vmlinux-4.1.34-33-debug.gz
DUMPFILE: /var/crash/2016-10-31-17:01//vmcore
CPUS: 4
DATE: Mon Oct 31 13:01:36 2016
UPTIME: 02:12:08
LOAD AVERAGE: 0.00, 0.00, 0.00
TASKS: 204
NODENAME: eje-code
RELEASE: 4.1.34-33-debug
VERSION: #1 SMP Thu Oct 20 08:03:29 UTC 2016 (fe18aba)
MACHINE: x86_64 (2094 Mhz)
MEMORY: 4 GB
PANIC: "sysrq: SysRq : Trigger a crash"
PID: 3260
COMMAND: "crashtest"
TASK: ffff88011a020550 [THREAD_INFO: ffff8800bcd98000]
CPU: 3
STATE: TASK_RUNNING (SYSRQ)
crash> extend /usr/lib64/crash/extensions/gcore.so
/usr/lib64/crash/extensions/gcore.so: shared object loaded
crash> gcore -f 0 -v 7 3260
gcore: Opening file core.3260.crashtest ...
gcore: done.
gcore: Writing ELF header ...
gcore: done.
gcore: Retrieving and writing note information ...
Segmentation fault
Sixty-four bytes of core get written before the segmentation fault (I'm guessing
that's the ELF header). I can gcore some other processes (although I get many
"gcore: WARNING: page fault at 7ffca6a5d000" errors). I tried this both with an
echo from bash from the command line and a custom test program that just does a controlled
crash in a function nested four deep. The segmentation fault sometimes causes a hang
(which I can end with Ctrl-C).
It does the same thing if I specify the task address (in this case, "gcore
ffff88011a020550"). I've tried it without any options, too, and with different
combinations.
I obtained a core dump of gcore and this is my debugging session:
eje-code:~ # gdb /usr/lib64/crash/extensions/gcore.so /var/core/core.eje-code-crash-3074
GNU gdb (GDB; openSUSE Leap 42.1) 7.11.1
Copyright (C) 2016 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 "x86_64-suse-linux".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://bugs.opensuse.org/>;.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>;.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from /usr/lib64/crash/extensions/gcore.so...done.
warning: core file may not match specified executable file. [Not sure why ...]
[New LWP 3074]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
Core was generated by `crash /boot/vmlinux-4.1.34-33-debug.gz
/var/crash/2016-10-31-17:01//vmcore'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0 0x0000000000000000 in ?? ()
Missing separate debuginfos, use: zypper install glibc-debuginfo-2.19-17.4.x86_64
liblzma5-debuginfo-5.0.5-3.5.x86_64 libncurses5-debuginfo-5.9-53.4.x86_64
libz1-debuginfo-1.2.8-6.4.x86_64
(gdb) bt
#0 0x0000000000000000 in ?? ()
#1 0x00007f1235eed4e4 in restore_regs_syscall_context (target=0x6939df8, regs=0xf6f280,
active_regs=0x7ffefa968880)
at libgcore/gcore_x86.c:1656
#2 0x00007f1235eedcb6 in genregs_get (target=0x6939df8, regset=0x7f12360f6460
<x86_64_regsets>, size=216,
buf=0xf6f280) at libgcore/gcore_x86.c:1795
#3 0x00007f1235ee6438 in fill_write_thread_core_info (fp=0x59efb10, tc=0x6939df8,
dump_tc=0x6939df8, info=0xf6ee80,
view=0x7f12360f5d80 <x86_64_regset_view>, offset=0x7ffefa968ab0, total=0xf6ee98)
at libgcore/gcore_coredump.c:469
#4 0x00007f1235ee682c in fill_write_note_info (fp=0x59efb10, info=0xf6ee80, phnum=20,
offset=0x7ffefa968ab0)
at libgcore/gcore_coredump.c:566
#5 0x00007f1235ee4dd1 in gcore_coredump () at libgcore/gcore_coredump.c:112
#6 0x00007f1235eeeb8b in do_gcore (arg=0x0) at gcore.c:317
#7 0x00007f1235eee926 in cmd_gcore () at gcore.c:253
#8 0x0000000000472b8c in ?? ()
#9 0x0000000000000000 in ?? ()
(gdb) bt
#0 0x0000000000000000 in ?? ()
#1 0x00007f1235eed4e4 in restore_regs_syscall_context (target=0x6939df8, regs=0xf6f280,
active_regs=0x7ffefa968880)
at libgcore/gcore_x86.c:1656
#2 0x00007f1235eedcb6 in genregs_get (target=0x6939df8, regset=0x7f12360f6460
<x86_64_regsets>, size=216,
buf=0xf6f280) at libgcore/gcore_x86.c:1795
#3 0x00007f1235ee6438 in fill_write_thread_core_info (fp=0x59efb10, tc=0x6939df8,
dump_tc=0x6939df8, info=0xf6ee80,
view=0x7f12360f5d80 <x86_64_regset_view>, offset=0x7ffefa968ab0, total=0xf6ee98)
at libgcore/gcore_coredump.c:469
#4 0x00007f1235ee682c in fill_write_note_info (fp=0x59efb10, info=0xf6ee80, phnum=20,
offset=0x7ffefa968ab0)
at libgcore/gcore_coredump.c:566
#5 0x00007f1235ee4dd1 in gcore_coredump () at libgcore/gcore_coredump.c:112
#6 0x00007f1235eeeb8b in do_gcore (arg=0x0) at gcore.c:317
#7 0x00007f1235eee926 in cmd_gcore () at gcore.c:253
#8 0x0000000000472b8c in ?? ()
#9 0x0000000000000000 in ?? ()
(gdb) up
#1 0x00007f1235eed4e4 in restore_regs_syscall_context (target=0x6939df8, regs=0xf6f280,
active_regs=0x7ffefa968880)
at libgcore/gcore_x86.c:1656
1656 regs->sp = gxt->get_old_rsp(target->processor);
(gdb) print gxt
$1 = (struct gcore_x86_table *) 0x215ea0 <gcore_x86_table>
(gdb) print *target
$2 = {task = 18446612137045525840, thread_info = 18446612135482589184, pid = 3260, comm =
"crashtest\000@XI\215u H",
processor = 3, ptask = 18446612137046565648, mm_struct = 18446612137048351232, tc_next =
0x0}
(gdb) print *regs
$3 = {r15 = 0, r14 = 2, r13 = 2, r12 = 34324496, bp = 2, bx = 4196186, r11 = 582, r10 =
140728806957456,
r9 = 140048302249728, r8 = 34324720, ax = 18446744073709551578, cx = 140048297135408, dx
= 2, si = 140048302292992,
di = 3, orig_ax = 1, ip = 140048297135408, cs = 51, flags = 582, sp = 140728806957864,
ss = 43, fs_base = 0,
gs_base = 0, ds = 0, es = 0, fs = 0, gs = 0}
(gdb) print *gxt
$4 = {get_old_rsp = 0x0, get_thread_struct_fpu = 0x0, get_thread_struct_fpu_size = 0x0,
is_special_syscall = 0x0,
is_special_ia32_syscall = 0x0, tsk_used_math = 0x0}
=============================
So not only is get_old_rsp zero, all the fields in gxt are zero.
Looks like a kernel support issue. This field is filled in by
gcore_x86_table_register_get_old_rsp() which looks up four symbols in various forms, none
of which exist in my kernel:
eje-code:~ # fgrep old_rsp /proc/kallsyms
eje-code:~ # fgrep cpu_pda /proc/kallsyms
eje-code:~ #
old_rsp did exist in openSUSE 12.1 and 13.1 (3.11.10-29 for the latter).
According to http://lists.openwall.net/linux-kernel/2015/03/17/766 old_rsp was renamed
rsp_scratch. I don't know if the semantics changed -- it doesn't appear so -- but
I added code to accept this symbol as an alternative and the core dump generates and works
(I can see a correct backtrace). I do not warrant the work though. :-) Someone may want
to review my work, and check the other functions and see if they are supposed to be zero.
Since they haven't been invoked I don't know if they are supposed to be non-zero
or not.
Here is the diff:
--- gcore_x86.c~ 2014-11-06 04:58:47.000000000 -0500
+++ gcore_x86.c 2016-10-31 16:01:00.989025841 -0400
@@ -1351,6 +1351,26 @@ static ulong gcore_x86_64_get_old_rsp(in
}
/**
+ * gcore_x86_64_get_rsp_scratch() - get rsp at per-cpu area
+ *
+ * @cpu target CPU's CPU id
+ *
+ * Given a CPU id, returns a RSP value saved at per-cpu area for the
+ * CPU whose id is the given CPU id.
+ */
+static ulong gcore_x86_64_get_rsp_scratch(int cpu)
+{
+ ulong old_rsp;
+
+ readmem(symbol_value("rsp_scratch") + kt->__per_cpu_offset[cpu],
+ KVADDR, &old_rsp, sizeof(old_rsp),
+ "gcore_x86_64_get_rsp_scratch: rsp_scratch",
+ gcore_verbose_error_handle());
+
+ return old_rsp;
+}
+
+/**
* gcore_x86_64_get_per_cpu__old_rsp() - get rsp at per-cpu area
*
* @cpu target CPU's CPU id
@@ -1834,6 +1854,11 @@ static void gcore_x86_table_register_get
else if (symbol_exists("_cpu_pda"))
gxt->get_old_rsp = gcore_x86_64_get_cpu__pda_oldrsp;
+
+ else if (symbol_exists("rsp_scratch"))
+ gxt->get_old_rsp = gcore_x86_64_get_rsp_scratch;
+
+ if (!gxt->get_old_rsp) printf ("Warning: NO gxt->get_old_rsp\n");
}
#endif