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Remote Debugging with GDB Print

 

Note: Using this application note on SmartFusion2 targets requires disabling cache in the kernel. Please turn off the CONFIG_M2S_CACHE kernel configuration option. This is done in the kernel build-time configuration, specifically: System Type -> M2S I/O Configuration -> Enable SmartFusion2 cache.

Step through the following procedure in order to start remote debugging with gdbserver:

  1. Go to the top of your Linux Cortex-M installation and activate a Linux Cortex-M development session:
  2. [psl@pvr linux-cortexm-x.x.x]$ . ACTIVATE.sh

  3. Make sure your target board has TCP/IP configured and up in Linux:
  4. ~ # ifconfig eth0
    eth0 Link encap:Ethernet HWaddr C0:B1:3C:83:83:83
    inet addr:172.17.5.100 Bcast:172.17.255.255 Mask:255.255.0.0
    UP BROADCAST MULTICAST MTU:1500 Metric:1
    RX packets:0 errors:0 dropped:0 overruns:0 frame:0
    TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
    collisions:0 txqueuelen:1000
    RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
    Interrupt:12

  5. It is recommended to rebuild your application with special GCC options. If your target is Cortex-M3, use the following options:
  6. [psl@pvr app]$ arm-uclinuxeabi-gcc -o app app.c -mcpu=cortex-m3 -mthumb -O0 -g

    If your target is Cortex-M4, do the following instead:

    [psl@pvr app]$ arm-uclinuxeabi-gcc -o app app.c -mcpu=cortex-m4 -mthumb -O0 -g

  7. Make your application binary (app, not app.gdb) and the gdbserver binary
    (${INSTALL_ROOT}/A2F/root/usr/bin/gdbserver) accessible from the target. You can NFS-mount some host directory from the target for that purpose or put these binaries to the initramfs list of your kernel image.
  8. Run gdbserver on the target (assuming /mnt is NFS-mounted to the host):
  9. ~ # /mnt/gdbserver :1234 /mnt/app

  10. Run GDB on the development host:
  11. [psl@pvr app]$ arm-uclinuxeabi-gdb ./app.gdb
    GNU gdb (GDB) 7.2.50.20100908-cvs
    Copyright (C) 2010 Free Software Foundation, Inc.
    License GPLv3+: GNU GPL version 3 or later
    <http://www.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 "--host=i686-linux --target=arm-uclinuxeabi".
    For bug reporting instructions, please see:
    <http://www.gnu.org/software/gdb/bugs/>
    ...
    Reading symbols from /home/work/psl/SF/devel/linux-cortexm-1.4.0/projects/gdbtest/app/app.gdb...done.
    (gdb)

  12. Establish a connection to the target:
  13. (gdb) target remote 172.17.5.100:1234
    Remote debugging using 172.17.5.100:1234 0x64030044 in _stext ()

  14. Debug your application using the standard GDB commands. Here is a sample debug session:
  15. (gdb) b main
    Breakpoint 1 at 0x640300ee: file app.c, line 16.
    (gdb) c
    Continuing.

    Breakpoint 1, main () at app.c:16
    16 a = 10;
    (gdb) n
    18 b = 20;
    (gdb) p a
    $1 = 10
    (gdb) n
    20 ret = func(a,b);
    (gdb) p b
    $2 = 20
    (gdb) s
    func (a=10, b=20) at app.c:5
    5 int c = (a+b)/2;
    (gdb) n
    7 printf("%s: (%d + %d)/2 = %d\n", __func__, a, b, c);
    (gdb) p c
    $3 = 15
    (gdb) bt
    #0 func (a=10, b=20) at app.c:7
    #1 0x64030102 in main () at app.c:20
    (gdb) n
    9 return c;
    (gdb) n
    10 }
    (gdb) fini
    Run till exit from #0 func (a=10, b=20) at app.c:10
    0x64030102 in main () at app.c:20
    20 ret = func(a,b);
    Value returned is $4 = 15
    (gdb)