remote kernel gdb stack frames corrupted after breakpoint or step

Stephan Uphoff ups at tree.com
Wed Sep 15 15:18:07 PDT 2004


I wrote a patch that should fix the problem for i386.

	http://www.freebsd.org/cgi/query-pr.cgi?pr=71715

Stephan

On Wed, 2004-09-15 at 17:52, Andrew Gallatin wrote:
> Kip McAtee writes:
>  > Greetings-
>  >
>  > I'm building on 5.3-BETA4 (and 6.0 current)
>  > with gdb (and kgdb) 6.1.1.
>  >
>  > I can get into the remote kernel debugger with
>  > sysctl debug.kdb.enter=1
>  >
>  > I can set a breakpoint and continue.
>  > When it hits the breakpoint I get:
>  >
>  > Breakpoint 2, wakeup (ident=0xc0c0f9e8) at ../../../kern/kern_synch.c:253
>  > 253             sleepq_broadcast(ident, SLEEPQ_MSLEEP, -1);
>  > (kgdb) c
>  > Continuing.
>  >
>  > Program received signal SIGSEGV, Segmentation fault.
>  >
>  > Looking at the backtrace implies that the stack frames
>  > are not displayed correctly. I'm setting:
>  >
> 
> FWIW, I see the same thing when continuing from breakpoints in
> RELENG_5 via ddb.  I've appended a log from my serial console.
> 
> Interestingly, dropping into the debugger via break on console works
> like a charm, its only inserted breakpoints which don't work.
> I think this started happening after the ddb->kdb conversion.
> 
> Drew
> 
> [send halt on serial console]
> db> break sched_switch
> db> c
> [thread 100004]
> Stopped at      sched_switch+0x1:       movl    %esp,%ebp
> db> tr
> sched_switch(1,0,0,0,0) at sched_switch+0x1
> idle_proc(0,e3f78d48,10e90,10e98,10ea0) at idle_proc+0x143
> fork_exit(c04fa329,0,e3f78d48) at fork_exit+0x80
> fork_trampoline() at fork_trampoline+0x8
> --- trap 0x1, eip = 0, esp = 0xe3f78d7c, ebp = 0 ---
> db> c
> 
> 
> kernel trap 12 with interrupts disabled
> 
> 
> Fatal trap 12: page fault while in kernel mode
> cpuid = 0; apic id = 00
> fault virtual address   = 0x0
> fault code              = supervisor read, page not present
> instruction pointer     = 0x8:0xc0527256
> stack pointer           = 0x10:0xe3f78c8c
> frame pointer           = 0x10:0xe3f78c9c
> code segment            = base 0x0, limit 0xfffff, type 0x1b
>                         = DPL 0, pres 1, def32 1, gran 1
> processor eflags        = resume, IOPL = 0
> current process         = 12 (idle: cpu0)
> [thread 100004]
> Stopped at      sched_switch+0xe:       movl    0(%ebx),%edx
> db> tr
> sched_switch(0,10,44096318,47c326eb,ffc00014) at sched_switch+0xe
> end(74c085d0,b816,a3640000,c,89d0558b) at 0xc1562640
> db> call cpu_reset
> cpu_reset called on cpu#0
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