gnu/60732: [PATCH] unbreak kgdb backtraces through traps
Peter Edwards
pmedwards at eircom.net
Tue Dec 30 09:00:59 PST 2003
>Number: 60732
>Category: gnu
>Synopsis: [PATCH] unbreak kgdb backtraces through traps
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Tue Dec 30 09:00:38 PST 2003
>Closed-Date:
>Last-Modified:
>Originator: Peter Edwards
>Release: 5.2-CURRENT
>Organization:
>Environment:
FreeBSD hippo 5.2-CURRENT FreeBSD 5.2-CURRENT #0: Mon Dec 29 21:20:38 GMT 2003 petere at hippo:/scratch/obj/scratch/src/sys/HIPPO i386
>Description:
This has been bugging the hell out of me for ages: I finally cleaned up
my local patch enough to consider submitting it.
The usr/src/gnu/usr.bin/binutils/gdb directory contains some freebsd-specific code to enable kernel debugging, uthread manipulation
etc.
There's a set of files, fbsd-kgdb-${GDB_CPU}.h, that are supposed to
provide hooks to the gdb base code. However, these are never included.
For i386, the main loss is the definition of "FRAME_SAVED_PC", which
is designed to aid gdb unwind through a stack frame. Without this
definition, the topmost frame of a core from kernel panic under the actual trap() frame is lost: This is normally the most interesting frame
>How-To-Repeat:
Find a way to kill your machine with a page fault (some available on request :-)) As an example, here's a backtrace for a panic I can reproduce at will: (note "calltrap" appears in frame 5)
#0 doadump () at /scratch/src/sys/kern/kern_shutdown.c:240
#1 0xc04c0489 in boot (howto=260) at /scratch/src/sys/kern/kern_shutdown.c:372
#2 0xc04c0868 in panic () at /scratch/src/sys/kern/kern_shutdown.c:550
#3 0xc05dc326 in trap_fatal (frame=0xd72e7c40, eva=0)
at /scratch/src/sys/i386/i386/trap.c:821
#4 0xc05db903 in trap (frame=
{tf_fs = 24, tf_es = -684851184, tf_ds = -1067712496, tf_edi = 0, tf_esi = -1067086800, tf_ebp = -684819296, tf_isp = -684819348, tf_ebx = -1000238144, tf_edx = -1050979712, tf_ecx = -1050979712, tf_eax = 20, tf_trapno = 12, tf_err = 0, tf_eip = -1068595426, tf_cs = 8, tf_eflags = 65683, tf_esp = -1050982468, tf_ss = 131})
at /scratch/src/sys/i386/i386/trap.c:250
#5 0xc05c9898 in calltrap () at {standard input}:94
#6 0xc04e8fa4 in turnstile_wait (ts=0x0, lock=0xc06560e0, owner=0x0)
at /scratch/src/sys/kern/subr_turnstile.c:510
#7 0xc04b5af5 in _mtx_lock_sleep (m=0xc06560e0, opts=0, file=0x0, line=0)
at /scratch/src/sys/kern/kern_mutex.c:476
#8 0xc04aa4a4 in ithread_loop (arg=0xc15aa600) at /scratch/src/sys/kern/kern_intr.c:543
#9 0xc04a9130 in fork_exit (callout=0xc04aa2e0 <ithread_loop>, arg=0x0, frame=0x0)
at /scratch/src/sys/kern/kern_fork.c:793
With the fix in place, I get this stack trace:
#0 doadump () at /scratch/src/sys/kern/kern_shutdown.c:240
#1 0xc04c0489 in boot (howto=260) at /scratch/src/sys/kern/kern_shutdown.c:372
#2 0xc04c0868 in panic () at /scratch/src/sys/kern/kern_shutdown.c:550
#3 0xc05dc326 in trap_fatal (frame=0xd72e7c40, eva=0)
at /scratch/src/sys/i386/i386/trap.c:821
#4 0xc05db903 in trap (frame=
{tf_fs = 24, tf_es = -684851184, tf_ds = -1067712496, tf_edi = 0, tf_esi = -1067086800, tf_ebp = -684819296, tf_isp = -684819348, tf_ebx = -1000238144, tf_edx = -1050979712, tf_ecx = -1050979712, tf_eax = 20, tf_trapno = 12, tf_err = 0, tf_eip = -1068595426, tf_cs = 8, tf_eflags = 65683, tf_esp = -1050982468, tf_ss = 131})
at /scratch/src/sys/i386/i386/trap.c:250
#5 0xc04e871e in propagate_priority (td=0xc46193c0)
at /scratch/src/sys/kern/subr_turnstile.c:230
#6 0xc04e8fa4 in turnstile_wait (ts=0xc438a640, lock=0xc06560e0, owner=0x0)
at /scratch/src/sys/kern/subr_turnstile.c:510
#7 0xc04b5af5 in _mtx_lock_sleep (m=0xc06560e0, opts=0, file=0x0, line=0)
at /scratch/src/sys/kern/kern_mutex.c:476
#8 0xc04aa4a4 in ithread_loop (arg=0xc15aa600) at /scratch/src/sys/kern/kern_intr.c:543
#9 0xc04a9130 in fork_exit (callout=0xc04aa2e0 <ithread_loop>, arg=0x0, frame=0x0)
at /scratch/src/sys/kern/kern_fork.c:793
(This time frame 5 actually shows me the faulting code.)
>Fix:
I rejigged the makefile to create a tm.h that included the stock gdb version, and the freebsd kgdb-specific code (the target for nm.h sets a precident for this). For i386, this just envolved ripping out the bits that were not used anyway, and leaving in a working definition of FRAME_SAVED_PC.
For alpha, the existing version should work fine. The other platforms don't seem to have any support for FRAME_SAVED_PC yet anyway, so they shouldn't be affected. Here's the patch:
begin 644 gdb-frame-patch.txt
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`
end
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>Audit-Trail:
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