Re: kernel core debugging

On Nov 6, 2024, at 09:28, [email protected] <[email protected]> wrote:

>> On 6. Nov 2024, at 15:12, Mark Millard <[email protected]> wrote:
>> 
>> On Nov 6, 2024, at 01:44, [email protected] <[email protected]> wrote:
>> 
>>> is debugging a kernel panic by using kgdb or lldb on a core file
>>> supposed to work? At least it is not right now for me...
>> 
>> # kgdb /boot/kernel.GENERIC-NODEBUG/kernel /var/crash/vmcore.2
>> GNU gdb (GDB) 15.1 [GDB v15.1 for FreeBSD]
>> Copyright (C) 2024 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 "aarch64-portbld-freebsd15.0".
>> Type "show configuration" for configuration details.
>> For bug reporting instructions, please see:
>> <https://www.gnu.org/software/gdb/bugs/>.
>> 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 /boot/kernel.GENERIC-NODEBUG/kernel...
>> Reading symbols from /usr/lib/debug//boot/kernel.GENERIC-NODEBUG/kernel.debug...
>> 
>> Unread portion of the kernel message buffer:
>> KDB: enter: manual escape to debugger
>> 
>> Reading symbols from /boot/kernel.GENERIC-NODEBUG/uhid.ko...
>> Reading symbols from /usr/lib/debug//boot/kernel.GENERIC-NODEBUG/uhid.ko.debug...
>> Reading symbols from /boot/kernel.GENERIC-NODEBUG/wmt.ko...
>> Reading symbols from /usr/lib/debug//boot/kernel.GENERIC-NODEBUG/wmt.ko.debug...
>> Reading symbols from /boot/kernel.GENERIC-NODEBUG/ums.ko...
>> Reading symbols from /usr/lib/debug//boot/kernel.GENERIC-NODEBUG/ums.ko.debug...
>> Reading symbols from /boot/kernel.GENERIC-NODEBUG/zfs.ko...
>> Reading symbols from /usr/lib/debug//boot/kernel.GENERIC-NODEBUG/zfs.ko.debug...
>> 0xffff00000050f3f0 in doadump (textdump=0, textdump@entry=212431136) at /home/pkgbuild/worktrees/main/sys/kern/kern_shutdown.c:404
>> warning: 404 /home/pkgbuild/worktrees/main/sys/kern/kern_shutdown.c: No such file or directory
>> (kgdb) bt
>> #0  0xffff00000050f3f0 in doadump (textdump=0, textdump@entry=212431136) at /home/pkgbuild/worktrees/main/sys/kern/kern_shutdown.c:404
>> #1  0xffff0000000ee6a8 in db_dump (dummy=<optimized out>, dummy2=<optimized out>, dummy3=<optimized out>, dummy4=<optimized out>) at /home/pkgbuild/worktrees/main/sys/ddb/db_command.c:596
>> #2  0xffff0000000ee478 in db_command (last_cmdp=<optimized out>, cmd_table=<optimized out>, dopager=true) at /home/pkgbuild/worktrees/main/sys/ddb/db_command.c:508
>> #3  0xffff0000000ee150 in db_command_loop () at /home/pkgbuild/worktrees/main/sys/ddb/db_command.c:555
>> #4  0xffff0000000f1ff4 in db_trap (type=<optimized out>, code=<optimized out>) at /home/pkgbuild/worktrees/main/sys/ddb/db_main.c:267
>> #5  0xffff000000568b0c in kdb_trap (type=60, code=0, tf=<optimized out>) at /home/pkgbuild/worktrees/main/sys/kern/subr_kdb.c:790
>> #6  <signal handler called>
>> #7  kdb_enter (why=<optimized out>, msg=<optimized out>) at /home/pkgbuild/worktrees/main/sys/kern/subr_kdb.c:556
>> #8  0xffff0000003625cc in vt_machine_kbdevent (vd=<optimized out>, c=<optimized out>) at /home/pkgbuild/worktrees/main/sys/dev/vt/vt_core.c:761
>> #9  vt_processkey (kbd=0xffffa000803caa80, vd=0xffff000000d24360 <vt_consdev>, c=-2147483514) at /home/pkgbuild/worktrees/main/sys/dev/vt/vt_core.c:903
>> #10 vt_kbdevent (kbd=0xffffa000803caa80, event=<optimized out>, arg=0xffff000000d24360 <vt_consdev>) at /home/pkgbuild/worktrees/main/sys/dev/vt/vt_core.c:1030
>> #11 0xffff0000001ea048 in kbdmux_intr (kbd=0xffffa000803caa80, arg=<optimized out>) at /home/pkgbuild/worktrees/main/sys/dev/kbdmux/kbdmux.c:565
>> #12 0xffff0000005839ac in taskqueue_run_locked (queue=queue@entry=0xffffa000803c9c00) at /home/pkgbuild/worktrees/main/sys/kern/subr_taskqueue.c:517
>> #13 0xffff000000583714 in taskqueue_run (queue=0xffffa000803c9c00) at /home/pkgbuild/worktrees/main/sys/kern/subr_taskqueue.c:532
>> #14 0xffff0000004bc114 in intr_event_execute_handlers (ie=0xffffa0008028ec00, p=<optimized out>) at /home/pkgbuild/worktrees/main/sys/kern/kern_intr.c:1183
>> #15 ithread_execute_handlers (ie=0xffffa0008028ec00, p=<optimized out>) at /home/pkgbuild/worktrees/main/sys/kern/kern_intr.c:1196
>> #16 ithread_loop (arg=<optimized out>, arg@entry=0xffffa000803de5a0) at /home/pkgbuild/worktrees/main/sys/kern/kern_intr.c:1289
>> #17 0xffff0000004b700c in fork_exit (callout=0xffff0000004bbd78 <ithread_loop>, arg=0xffffa000803de5a0, frame=0xffff00010ca97a00) at /home/pkgbuild/worktrees/main/sys/kern/kern_fork.c:1151
>> #18 <signal handler called>
>> 
>> The context here was from an official PkgBase kernel and world
>> installation.
>> 
>> . . . (deletion) . . .
>> 
>> You may have to be more explicit about the specific of the
>> problem(s) you are seeing.
> OK. Here is what I am referring to:
> 
> tuexen@head:~ % sudo kgdb -c /var/crash/vmcore.last /boot/kernel/kernel

That command does not match the parameter order in the man page or
in my example.

man kgdb output shows kernel first, then core:

SYNOPSIS
     kgdb [-a | -f | -fullname] [-b rate] [-q | -quiet] [-v] [-w]
          [-d crashdir] [-c core | -n dumpnr | -r device] [kernel [core]]

My example: # kgdb /boot/kernel.GENERIC-NODEBUG/kernel /var/crash/vmcore.2

You might want to see if using the other order makes a difference.

> Password:
> GNU gdb (GDB) 15.1 [GDB v15.1 for FreeBSD]
> Copyright (C) 2024 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 "aarch64-portbld-freebsd15.0".
> Type "show configuration" for configuration details.
> For bug reporting instructions, please see:
> <https://www.gnu.org/software/gdb/bugs/>.
> 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 /boot/kernel/kernel...
> Reading symbols from /usr/lib/debug//boot/kernel/kernel.debug...
> 
> Unread portion of the kernel message buffer:
> panic: tcp_do_segment: sent too much
> cpuid = 1
> time = 1730910226
> KDB: stack backtrace:
> db_trace_self() at db_trace_self
> db_trace_self_wrapper() at db_trace_self_wrapper+0x38
> vpanic() at vpanic+0x1a0
> panic() at panic+0x48
> tcp_do_segment() at tcp_do_segment+0x2794
> tcp_input_with_port() at tcp_input_with_port+0xcbc
> tcp_input() at tcp_input+0x10
> ip_input() at ip_input+0x35c
> netisr_dispatch_src() at netisr_dispatch_src+0xd8
> tunwrite() at tunwrite+0x2a8
> devfs_write_f() at devfs_write_f+0x108
> dofilewrite() at dofilewrite+0x7c
> kern_writev() at kern_writev+0x4c
> sys_writev() at sys_writev+0x40
> do_el0_sync() at do_el0_sync+0x60c
> handle_el0_sync() at handle_el0_sync+0x4c
> --- exception, esr 0x56000000
> KDB: enter: panic
> 
> Reading symbols from /boot/kernel/tcp_rack.ko...
> Reading symbols from /usr/lib/debug//boot/kernel/tcp_rack.ko.debug...
> Reading symbols from /boot/kernel/tcphpts.ko...
> Reading symbols from /usr/lib/debug//boot/kernel/tcphpts.ko.debug...
> Reading symbols from /boot/kernel/if_bridge.ko...
> Reading symbols from /usr/lib/debug//boot/kernel/if_bridge.ko.debug...
> Reading symbols from /boot/kernel/bridgestp.ko...
> Reading symbols from /usr/lib/debug//boot/kernel/bridgestp.ko.debug...
> Reading symbols from /boot/kernel/uhid.ko...
> Reading symbols from /usr/lib/debug//boot/kernel/uhid.ko.debug...
> Reading symbols from /boot/kernel/wmt.ko...
> Reading symbols from /usr/lib/debug//boot/kernel/wmt.ko.debug...
> Reading symbols from /boot/kernel/cc_newreno.ko...
> Reading symbols from /usr/lib/debug//boot/kernel/cc_newreno.ko.debug...
> 0xffff0000004b5644 in doadump (textdump=0) at /usr/home/tuexen/freebsd-src/sys/kern/kern_shutdown.c:404
> 404 dump_savectx();
> (kgdb) up
> #1  0x3fdb0000000e99f0 in ?? ()
> (kgdb)  Initial frame selected; you cannot go up.
> (kgdb)  Initial frame selected; you cannot go up.
> (kgdb) quit
> tuexen@head:~ % pkg info gdb  gdb-15.1
> Name           : gdb
> Version        : 15.1
> Installed on   : Thu Oct 24 10:32:17 2024 CEST
> Origin         : devel/gdb
> Architecture   : FreeBSD:15:aarch64
> Prefix         : /usr/local
> Categories     : devel
> Licenses       : GPLv3
> Maintainer     : [email protected]
> WWW            : https://www.gnu.org/software/gdb/
> Comment        : GNU Project Debugger
> Options        :
> BUNDLED_READLINE: off
> BUNDLED_ZLIB   : off
> DEBUGINFOD     : off
> GDB_LINK       : on
> GUILE          : off
> KGDB           : on
> NLS            : on
> PORT_ICONV     : on
> PORT_READLINE  : on
> PYTHON         : on
> SOURCE_HIGHLIGHT: on
> SYSTEM_ICONV   : off
> SYSTEM_ZLIB    : on
> TUI            : on
> XXHASH         : on
> Shared Libs required:
> libzstd.so.1
> libxxhash.so.0
> libsource-highlight.so.4
> libreadline.so.8
> libpython3.11.so.1.0
> libmpfr.so.6
> libintl.so.8
> libiconv.so.2
> libgmp.so.10
> libexpat.so.1
> libboost_regex.so.1.85.0
> Annotations    :
> FreeBSD_version: 1500025
> build_timestamp: 2024-10-16T20:27:27+0000
> built_by       : poudriere-git-3.4.2
> cpe            : cpe:2.3:a:gnu:gdb:15.1:::::freebsd15:aarch64
> flavor         : py311
> port_checkout_unclean: no
> port_git_hash  : 82beca9e630
> ports_top_checkout_unclean: no
> ports_top_git_hash: 94c4ac6b071
> repo_type      : binary
> repository     : FreeBSD
> Flat size      : 58.5MiB
> Description    :
> GDB is a source-level debugger for Ada, C, C++, Objective-C, Pascal and
> many other languages.  GDB can target (i.e., debug programs running on)
> more than a dozen different processor architectures, and GDB itself can
> run on most popular GNU/Linux, Unix and Microsoft Windows variants.
> tuexen@head:~ % 
> 
> Using kgdb from "pkg install gdb" and locally built world and kernel.
> 
> Best regards
> Michael
>> 
>> For reference:
>> 
>> . . . (deletion) . . .



===
Mark Millard
marklmi at yahoo.com