KGDB problem at first breakpoint

[Nuno Martins]

On Wed, May 18, 2011 at 12:23 PM, Prabhu nath <gprabhunath at gmail.com> wrote:
> Dear All,
>        There is a problem with the KGDB at the very first break point after
> executing the gdb command "target remote /dev/ttyS0" from the host.
>        I have verbatim, followed the KGDB
> document http://kernel.org/pub/linux/kernel/people/jwessel/kdb/
> Problem Logs:
> ---------------------
> Details  of my hardware and system software:
> -------------------------------------------------------------------
> Host (Development machine):
>                       Intel Pentium IV Machine with Fedora Core 12
>                       Linux Version : 2.6.31.5-127.fc12.i686.PAE
>                       gdb version : GNU gdb (GDB) Fedora (7.0-3.fc12)
> Target:
>                  Intel Pentium IV Machine with Fedora Core 12
>                  Customized Linux Version :  2.6.38
> Host is connected to Target via a null modem cable
> Snapshot of .config of linux version 2.6.38 on the target
> # CONFIG_DEBUG_RODATA is not set
> CONFIG_HAVE_ARCH_KGDB=y
> CONFIG_FRAME_POINTER=y
> CONFIG_DEBUG_INFO=y
> CONFIG_KGDB=y
> CONFIG_KGDB_SERIAL_CONSOLE=y
> CONFIG_KGDB_LOW_LEVEL_TRAP=y
> Grub config on the target machine
> title Fedora (2.6.38)
>         root (hd0,0)
>         kernel /boot/vmlinuz-2.6.38 ro
> root=UUID=fb7800fb-cfe7-438d-bc7f-c153ba4353d1  LANG=en_US.UTF-8
> SYSFONT=latarcyrheb-sun16 KEYBOARDTYPE=pc KEYTABLE=usconsole=ttyS0,115200n8
> kgdboc=ttyS0 kgdbwait
>         initrd /boot/initrd-2.6.38.img
Do you have other serial line that you can connect to ? If you have
you could try to connect the console or the kgdboc to other serial
line.
This way you can have each on it's private serial line. I don't know
if it can multiplex the signal.

>
> On power on of the target, linux kernel boots and the logs are seen on the
> minicom console of the host and it will wait for the gdb on the host to
> connect. Here is the last 4 lines of the logs seen on the minicom
> Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
> serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
> 00:06: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
> kgdb: Registered I/O driver kgdboc.
> kgdb: Waiting for connection from remote gdb..
> --- Now I close the minicom console (Ctrl-A X) and start the gdb on the
> host. Here is the steps I follow.
> On the host machine:
>
> [root at localhost kgdb]# gdb vmlinux
> GNU gdb (GDB) Fedora (7.0-3.fc12)
> Copyright (C) 2009 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 "i686-redhat-linux-gnu".
> For bug reporting instructions, please see:
> <http://www.gnu.org/software/gdb/bugs/>...
> Reading symbols from /root/kgdb/vmlinux...done.
> (gdb) set remotebaud 115200
> (gdb) set debug remote 1
> (gdb) target remote /dev/ttyS0
> Remote debugging using /dev/ttyS0
> Sending packet: $qSupported#37...Ack
> Packet received:
> Packet qSupported (supported-packets) is NOT supported
> Sending packet: $Hg0#df...Ack
> Packet received: OK
> Sending packet: $?#3f...Ack
> Packet received: S05
> Sending packet: $Hc-1#09...Ack
> Packet received: OK
> Sending packet: $qC#b4...Ack
> Packet received: QC01
> Sending packet: $qAttached#8f...Ack
> Packet received:
> Packet qAttached (query-attached) is NOT supported
> Sending packet: $qOffsets#4b...Ack
> Packet received:
> Sending packet: $g#67...Ack
> Packet received:
> 36000000ffffffff0abaffff20d98bc06c3f86de783f86de803ac8dd803f86de885747c00202000060000000680000007b00c8dd7b0086deffff0000ffff0000
> Sending packet: $mc0475788,1#a4...Ack
> Packet received: 0f
> Sending packet: $mc0475788,8#ab...Ack
> Packet received: 0faef889f6ff0d08
> Sending packet: $mc0475788,7#aa...Ack
> Packet received: 0faef889f6ff0d
> 0xc0475788 in ?? ()
> Sending packet: $qSymbol::#5b...Ack
> Packet received:
> Packet qSymbol (symbol-lookup) is NOT supported
> (gdb) s
> Cannot find bounds of current function
> (gdb)
>
> Observation:
>                      1. Ideally the kernel being debugged should break at
> legitimate address and the corresponding line number should
>                          be displayed instead of " 0xc0475788 in ?? ()".
>                      2. On inspecting section header in vmlinux executable,
> I found the .text section address range is from
>                          0xC1000000 to 0xC1326e58  and no section's contents
> associate with the address 0xC0475788.
>                      3. Hence on single stepping, gdb logs the error
> as "Cannot find bounds of current function"
>  Humbly request you to help me in addressing this issue.
> Thanks and Regards,
> Prabhu
>
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>



-- 
Nuno Martins