[Qemu-devel] Re: How to debug Linux kernel on qemu with kgdb?

["Neo Jia" <neojia@gmail.com>]

On 4/25/07, Jan Kiszka <jan.kiszka@web.de> wrote:
> Neo Jia wrote:
> > On 4/25/07, Jan Kiszka <jan.kiszka@web.de> wrote:
> >> Neo Jia wrote:
> >> > On 4/25/07, Jan Kiszka <jan.kiszka@web.de> wrote:
> >> >> Neo Jia wrote:
> >> >> > On 4/25/07, Jan Kiszka <jan.kiszka@web.de> wrote:
> >> >> >> Neo Jia wrote:
> >> >> >> > hi,
> >> >> >> >
> >> >> >> > I am trying to use debug kgdb patched linux kernel on my qemu.
> >> Both
> >> >> >> > the native and target platform are IA32. I am wondering if
> >> there is
> >> >> >> > anyone can show me the procedure?
> >> >> >>
> >> >> >> Yep, see
> >> >> https://mail.gna.org/public/xenomai-core/2006-09/msg00202.html
> >> >> >>
> >> >> >> (BTW, I think that kgdb bug is still unfixed - I never got a
> >> >> feedback.)
> >> >> >
> >> >> > I can connect gdb through /dev/pts/XX. My qemu is lanuched by
> >> >> >
> >> >> > qemu -nographic -hda linux.img -kernel
> >> >> > ./2.6.15.5-kgdb/vmlinuz-2.6.15.5-kgdb -serial pty -append "kgdbwait
> >> >> > console=ttyS0 root=/dev/hda sb=0x220,5,1,5 ide2=noprobe ide3=noprobe
> >> >> > ide4=noprobe ide5=noprobe"
> >> >> >
> >> >> > Do you know where can I get the console output?
> >> >> >
> >> >>
> >> >> Use "... -serial stdio -serial pty ..." and attached kgdb to the
> >> second
> >> >> serial port (I think to recall that is default anyway). The first
> >> one is
> >> >> then used for the kernel console.
> >> >>
> >> >> > I would like to work out kgdb + qemu to debug linux kernel.
> >> >>
> >> >> ??? So you really want to debug the kernel when kgdb is applied, ie.
> >> >> actually debug kgdb? If you only intend to debug the kernel itself,
> >> qemu
> >> >> -s + gdb is enough.
> >> >
> >> > Jan,
> >> >
> >> > I just would like to debug kernel itself. I have tried qemu -s + gdb
> >> > but it keeps
> >> > getting "apic_timer_interrupt" when I am using "n" command.
> >> >
> >> > The following is the output:
> >> >
> >> >> gdb vmlinux
> >> > GNU gdb 6.5.50.20060621-cvs
> >> > Copyright (C) 2006 Free Software Foundation, Inc.
> >> > GDB 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.
> >> > Type "show copying" to see the conditions.
> >> > There is absolutely no warranty for GDB.  Type "show warranty" for
> >> details.
> >> > This GDB was configured as "i686-pc-linux-gnu"...Using host
> >> > libthread_db library "/lib/tls/libthread_db.so.1".
> >> >
> >> > (gdb) target remote localhost:1234
> >> > Remote debugging using localhost:1234
> >> > 0x0000fff0 in ?? ()
> >> > warning: shared library handler failed to enable breakpoint
> >> > (gdb) c
> >> > Continuing.
> >> >
> >> > Program received signal SIGINT, Interrupt.
> >> > default_idle () at include/asm/bitops.h:252
> >> > 252             return ((1UL << (nr & 31)) & (addr[nr >> 5])) != 0;
> >> > (gdb) b sys_ex
> >> > sys_execve      sys_exit        sys_exit_group
> >> > (gdb) b sys_execve
> >> > Breakpoint 1 at 0xc0101ac1: file arch/i386/kernel/process.c, line 791.
> >> > (gdb) c
> >> > Continuing.
> >> >
> >> > Breakpoint 1, sys_execve (regs=
> >> >      {ebx = 135197704, ecx = 135197864, edx = 135244936, esi =
> >> > 135197704, edi = 135197704, ebp = -1079176984, eax = 11, xds = 123,
> >> > xes = 123, orig_eax = 11, eip = -1208835017, xcs = 115, eflags = 582,
> >> > esp = -1079177012, xss = 123})
> >> >    at arch/i386/kernel/process.c:791
> >> > 791             filename = getname((char __user *) regs.ebx);
> >> > (gdb) n
> >> > 0xc0103666 in apic_timer_interrupt () at include/asm/current.h:9
> >> > 9       {
> >>
> >> That's normal. You stopped the kernel in sys_execve with interrupts
> >> enabled. When continuing, qemu replays any pending interrupts, here the
> >> timer. Thus your next instruction is not in sys_execve, but in the
> >> interrupt handler. You can try finish then and hope that you will return
> >> to the next line in sys_execve, or you put another breakpoint at the
> >> next interesting spot and just issue continue.
> >>
> >> Jan
> >>
> >>
> >> PS: Using kgdb from inside qemu should work (at least it once did for
> >> me), but it is really sloooow.
> >>
> >
> > Could you show me the procedure you did? I just want to use this to
> > learn kernel code.
>
> Did you redirect kgdb to ttyS1?

Yes, I just redirect kgdb to ttyS1 but still nothing. But if I
compiled with "CONFIG_KGDB_CONSOLE=y", it will show on the gdb
console.

Is a bug or wrong configuration?

Thanks,
Neo

>
> Jan
>
>
>


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