close

參考來源
http://www.denx.de/wiki/publish/DULG/DULG-tqm8xxl.html

 

10. Debugging

The purpose of this document is not to provide an introduction into programming and debugging in general. We assume that you know how to use the GNU debugger gdb and probably it's graphical frontends like ddd. We also assume that you have access to adequate tools for your work, i. e. a BDI2000 BDM/JTAG debugger. The following discussion assumes that the host name of your BDI2000 is bdi.

Please note that there are several limitations in earlier versions of GDB. The version of GDB as distributed with the ELDK contains several bug fixes and extensions. If you find that your GDB behaves differently, have a look at the GDB sources and patches that come with the ELDK source.

10.1. Debugging of U-Boot

When U-Boot starts it is running from ROM space. Running from flash would make it nearly impossible to read from flash while executing code from flash not to speak of updating the U-Boot image in flash itself. To be able to do just that, U-Boot relocates itself to RAM. We therefore have two phases with different program addresses. The following sections show how to debug U-Boot in both phases.

10.1.1. Debugging of U-Boot Before Relocation

Before relocation, the addresses in the ELF file can be used without any problems, so debugging U-Boot in this phase with the BDI2000 is quite easy: 

bash[0]$ ${CROSS_COMPILE}gdb u-boot
GNU gdb 5.1.1
Copyright 2002 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 "--host=i386-redhat-linux --target=ppc-linux"...

(gdb) target remote bdi:2001
Remote debugging using bdi:2001
0xfffffffc in ?? ()
(gdb) b cpu_init_f
Breakpoint 1 at 0xfffd3310: file cpu_init.c, line 136.
(gdb) c
Continuing.
 
Breakpoint 1, cpu_init_f () at cpu_init.c:136
136             asm volatile("  bl      0f"             ::: "lr");
(gdb) s
137             asm volatile("0:        mflr    3"              ::: "r3");
(gdb)
138             asm volatile("  addi    4, 0, 14"       ::: "r4");
(gdb)

cpu_init_f is the first C function called from the code in start.C.

10.1.2. Debugging of U-Boot After Relocation

For debugging U-Boot after relocation we need to know the address to which U-Boot relocates itself to. When no exotic features like PRAM are used, this address usually is <MAXMEM> - CFG_MONITOR_LEN. In our example with 16MB RAM and CFG_MONITOR_LEN = 192KB this yields the address 0x1000000 - 0x30000 = 0xFD0000. With this knowledge, we can instruct gdb to forget the old symbol table and reload the symbols with our calculated offset: 

(gdb) symbol-file
Discard symbol table from `/home/dzu/denx/cvs-trees/u-boot/u-boot'? (y or n) y
No symbol file now.
(gdb) add-symbol-file u-boot 0xfd0000
add symbol table from file "u-boot" at
        .text_addr = 0xfd0000
(y or n) y
Reading symbols from u-boot...done.
(gdb) b board_init_r
Breakpoint 2 at 0xfd?99ac: file board.c, line 533.
(gdb) c
Continuing.

Breakpoint 2, board_init_r (id=0xfbb1f0, dest_addr=16495088) at board.c:533
533     {
(gdb)

board_init_r is the first C routine running in the newly relocated C friendly RAM environment.

The simple example above relocates the symbols of only one section, .text. Other sections of the executable image (like .data, .bss, etc.) are not relocated and this prevents gdb from accessing static and global variables by name. See more sophisticated examples in section 10.3. GDB Startup File and Utility Scripts.

10.2. Linux Kernel Debugging

10.2.1. Linux Kernel and Statically Linked Device Drivers

10.2.2. Dynamically Loaded Device Drivers (Modules)

First start GDB in the root directory of your Linux kernel, using the vmlinux kernel image as file to debug: 

bash$ cd <linux-root>
bash$ ${CROSS_COMPILE}gdb vmlinux 
GNU gdb 5.1.1
Copyright 2002 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 "--host=i386-redhat-linux --target=ppc-linux".
(gdb)

Now attach to the target and start execution with the commands: 

(gdb) target remote bdi:2001
Remote debugging using bdi:2001
0x00000100 in ?? ()
(gdb) c
Continuing.

Now the target should boot Linux as usual. Next you need to load your kernel module on the target: 

bash# insmod -m ex_sw.o
Sections:       Size      Address   Align
.this           00000060  cf030000  2**2
.text           000002f4  cf030060  2**2
.rodata         00000134  cf030354  2**2
.data           00000000  cf030488  2**0
.sdata          0000000c  cf030488  2**2
.kstrtab        00000085  cf030494  2**0
.bss            00000000  cf030519  2**0
.sbss           00000008  cf03051c  2**2
...

The option -m prints out the addresses of the various code and data segments ( .text, .data, .sdata, .bss, .sbss ) after relocation. GDB needs these addresses to know where all the symbols are located. We now interrupt GDB to load the symbol table of the module as follows: 

(gdb) ^C
Program received signal SIGSTOP, Stopped (signal).
...
(gdb) add-symbol-file <path-to-module-dir>/ex_sw.o 0xcf030060\
 -s .rodata 0xcf030354\
 -s .data   0xcf030488\
 -s .sdata  0xcf030488\
 -s .bss    0xcf030519\
 -s .sbss   0xcf03051c
add symbol table from file "<path-to-module-dir>/ex_sw.o" at
        .text_addr = 0xcf030060
        .rodata_addr = 0xcf030354
        .data_addr = 0xcf030488
        .sdata_addr = 0xcf030488
        .bss_addr = 0xcf030519
        .sbss_addr = 0xcf03051c
(y or n) y
Reading symbols from <path-to-module-dir>/ex_sw.o...done.

Now you can list the source code of the module, set break points or inspect variables as usual: 

(gdb) l fun
61      static RT_TASK *thread;
62
63      static int cpu_used[NR_RT_CPUS];
64
65      static void fun(int t)
66      {
67              unsigned int loops = LOOPS;
68              while(loops--) {
69                      cpu_used[hard_cpu_id()]++;
70                      rt_leds_set_mask(1,t);
(gdb)
(gdb) b ex_sw.c:69
Breakpoint 1 at 0xcf03007c: file ex_sw.c, line 69.
(gdb) c
Continuing.
Breakpoint 1, fun (t=1) at ex_sw.c:69
69                      cpu_used[hard_cpu_id()]++;
(gdb) p ntasks
$1 = 16
(gdb) p stack_size
$2 = 3000

The next section demonstrates a way to automate the symbol table loading procedure.

10.2.3. GDB Macros to Simplify Module Loading

The following GDB macros and scripts help you to load kernel modules into GDB in a half-automatic way. It assumes, that the module on the target has been installed with the command: 

bash# insmod -m my_module.o > my_module.o.map

In your $HOME directory you need the scripts add-symbol-file.sh and the GDB startup file .gdbinit, which are listed in 10.3. GDB Startup File and Utility Scripts below.

Now you can include the symbol definition into GDB with: 

bash$ ${CROSS_COMPILE}gdb vmlinux 
GNU gdb 5.1.1
Copyright 2002 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 "--host=i386-redhat-linux --target=ppc-linux".
0x00000100 in ?? ()
c
Continuing.
^C
Program received signal SIGSTOP, Stopped (signal).
0xcf02a91c in ?? ()
(gdb) add-module rtai4/examples/sw/ex_sw.o
add symbol table from file "/HHL/8xx/target/home/wolf/rtai4/examples/sw/ex_sw.o" at
        .text_addr = 0xcf030060
        .rodata_addr = 0xcf030340
        .data_addr = 0xcf030464
        .sdata_addr = 0xcf030464
        .bss_addr = 0xcf0304f5
        .sbss_addr = 0xcf0304f8
(gdb) b ex_sw.c:69
Breakpoint 1 at 0xcf03007c: file ex_sw.c, line 69.
(gdb) c
Continuing.

Breakpoint 1, fun (t=0x1) at ex_sw.c:69
69                      cpu_used[hard_cpu_id()]++;
(gdb) p/d loops
$2 = 999986939
(gdb) p t
$3 = 0x1
(gdb) d b
Delete all breakpoints? (y or n) y
(gdb) c
Continuing.

10.3. GDB Startup File and Utility Scripts

In addition to the add-module macro, the followin example GDB startup file contains a few other useful settings and macros, which you may want to adjust to your local environment: 

set output-radix 16

target remote bdi:2001

define reset
        detach
        target remote bdi:2001
end

define add-module
        shell ~/add-symbol-file.sh $arg0
        source ~/add-symbol-file.gdb
end
document add-module
        Usage: add-module <module>

        Do add-symbol-file for module <module> automatically.
        Note: A map file with the extension ".map" must have
        been created with "insmod -m <module> > <module>.map"
        in advance.
end

The following shell script ~/add-symbol-file.sh is used to run the GDB add-symbol-file command automatically: 

#!/bin/sh
#
# Constructs the GDB "add-symbol-file" command string
# from the map file of the specified kernel module.

add_sect() {
    ADDR=`awk '/^'$1' / {print $3}' $MAPFILE`
    if [ "$ADDR" != "" ]; then
        echo "-s $1 0x`awk '/^'$1' / {print $3}' $MAPFILE`"
    fi
}

[ $# == 1 ] && [ -r "$1" ] || { echo "Usage: $0 <module>" >&2 ; exit 1 ; }

MAPFILE=$1.map

ARGS="0x`awk '/^.text / {print $3}' $MAPFILE`\
 `add_sect .rodata`\
 `add_sect .data`\
 `add_sect .sdata`\
 `add_sect .bss`\
 `add_sect .sbss`\
"

echo "add-symbol-file $1 $ARGS" > ~/add-symbol-file.gdb

10.4. Tips and Tricks

  • To prevent GDB from jumping around in the code when trying to single step, i. e. when it seems as if the code is not executing line by line, you can recompile your code with the following additional compiler options: 
    -fno-schedule-insns -fno-schedule-insns2
  • On some systems (like the MPC8xx or MPC8260) you can only define one hardware breakpoint. Therefore you must delete an existing breakpoint before you can define a new one: 
    (gdb) d b
Delete all breakpoints? (y or n) y
(gdb) b ex_preempt.c:63
Breakpoint 2 at 0xcf030080: file ex_preempt.c, line 63.

10.5. Application Debugging

10.5.1. Local Debugging

In case there is a native GDB available for your target you can use it for application debugging as usual: 

bash$ gcc -Wall -g -o hello hello.c 
bash$ gdb hello
...
(gdb) l
1       #include <stdio.h>
2
3       int main(int argc, char* argv[])
4       {
5               printf ("Hello world\n");
6               return 0;
7       }
(gdb) break 5
Breakpoint 1 at 0x8048466: file hello.c, line 5.
(gdb) run
Starting program: /opt/eldk/ppc_8xx/tmp/hello

Breakpoint 1, main (argc=0x1, argv=0xbffff9f4) at hello.c:5
5               printf ("Hello world\n");
(gdb) c
Continuing.
Hello world

Program exited normally.

10.5.2. Remote Debugging

gdbserver allows you to connect your program with a remote GDB using the "target remote" command. On the target machine, you need to have a copy of the program you want to debug. gdbserver does not need your program's symbol table, so you can strip the program if necessary to save space. GDB on the host system does all the symbol handling. Here is an example: 

bash$ ${CROSS_COMPILE}gcc -Wall -g -o hello hello.c
bash$ cp -p hello <directory-shared-with-target>/hello-stripped
bash$ ${CROSS_COMPILE}strip <directory-shared-with-target>/hello-stripped

To use the server, you must tell it how to communicate with GDB, the name of your program, and the arguments for your program. To start a debugging session via network type on the target: 

bash$ cd <directory-shared-with-host>
bash$ gdbserver 192.168.1.1:12345 hello-stripped
Process hello-stripped created; pid = 353

And then on the host: 

bash$ ${CROSS_COMPILE}gdb hello
...
(gdb) set solib-absolute-prefix /opt/eldk/$CROSS_COMPILE
(gdb) dir /opt/eldk/$CROSS_COMPILE
Source directories searched:
/opt/eldk/$CROSS_COMPILE:$cdir:$cwd
(gdb) target remote 192.168.1.99:12345
Remote debugging using 192.168.1.99:12345
0x30012748 in ?? ()
...
(gdb) l
1       #include <stdio.h>
2
3       int main(int argc, char* argv[])
4       {
5               printf ("Hello world\n");
6               return 0;
7       }
(gdb) break 5
Breakpoint 1 at 0x10000498: file hello.c, line 5.
(gdb) continue
Continuing.

Breakpoint 1, main (argc=1, argv=0x7ffffbe4) at hello.c:5
5               printf ("Hello world\n");
(gdb) p argc
$1 = 1
(gdb) continue
Continuing.

Program exited normally.

If the target program you want to debug is linked against shared libraries, you must tell GDB where the proper target libraries are located. This is done using the set solib-absolute-prefix GDB command. If this command is omitted, then, apparently, GDB loads the host versions of the libraries and gets crazy because of that.

10.6. Debugging with Graphical User Interfaces

It is convenient to use DDD, a Graphical User Interface to GDB, for debugging as it allows to define and execute frequently used commands via buttons. You can start DDD with the command: 

bash$ ddd --debugger ${CROSS_COMPILE}gdb &

If DDD is not already installed on your Linux system, have a look at your distribution media.

11. Simple Embedded Linux Framework

12. Books, Mailing Lists, Links, etc.

This section provides references on where to find more information

Contents:

12.1. Application Notes

A collection of Application Notes relevant for embedded computing can be found on the DENX web server.

12.2. Books

12.2.1. Linux kernel

  • Karim Yaghmour: "Building Embedded Linux Systems", Paperback: 400 pages, O'Reilly & Associates; (May 2003); ISBN 059600222X - IMHO the best book about Embedded Linux so far. An absolute must have.
  • Greg Kroah-Hartman: "Linux Kernel in a Nutshell", 198 pages, O'Reilly ("In Nutshell" series), (December 2006), ISBN 10: 0-596-10079-5; ISBN 13: 9780596100797
    - Tarball of PDF files (3 MB): http://www.kernel.org/pub/linux/kernel/people/gregkh/lkn/lkn_pdf.tar.bz2
    - Tarball of DocBook files (1 MB): http://www.kernel.org/pub/linux/kernel/people/gregkh/lkn/lkn_xml.tar.bz2
  • Craig Hollabaugh: "Embedded Linux: Hardware, Software, and Interfacing", Paperback: 432 pages; Addison Wesley Professional; (March 7, 2002); ISBN 0672322269
  • Christopher Hallinan: "Embedded Linux Primer: A Practical Real-World Approach", 576 pages, Prentice Hall, September 2006, ISBN-10: 0-13-167984-8; ISBN-13: 978-0-13-167984-9
  • The Linux Kernel - describing most aspects of the Linux Kernel. Probably, the first reference for beginners. Lots of illustrations explaining data structures use and relationships. In short: a must have.
  • Linux Kernel Module Programming Guide - Very nice 92 pages GPL book on the topic of modules programming. Lots of examples.
  • Jonathan Corbet, Alessandro Rubini, Greg Kroah-Hartman: "Linux Device Drivers", 3rd Edition ; Paperback: 636 pages; O'Reilly & Associates; 3rd edition (February 2005); ISBN: 0-596-00590-31 - The reference book for writing Linux device drivers. An absolute must have. => Read online
  • Jgen Quade, Eva-Katharina Kunst: "Linux-Treiber entwickeln"; Broschur: 436 pages; dpunkt.verlag, Juni 2004; ISBN 3898642380 - focused on kernel 2.6, unfortunately German only - => Read online
  • LWN: Porting device drivers to the 2.6 kernel - Series of articles (37) in Linux Weekly News: http://lwn.net/Articles/driver-porting/

12.2.2. General Linux / Unix programming

  • W. Richard Stevens: "Advanced Programming in the UNIX Environment", Addision Wesley, ISBN 0-201-56317-7
  • Eric S. Raymond: "The Art of Unix Programming", Addision Wesley, ISBN 0131429019 => Read online
  • David R. Butenhof: "Programming with POSIX Threads", Addision Wesley, ISBN 0-201-63392-2.
  • Bradford Nichols, Dick Buttlar and Jacqueline Proulx Farrell: "Pthreads Programming", O'Reilly & Associates

12.2.3. Network Programming

  • W. Richard Stevens: "TCP/IP Illustrated, Volume 1 - The Protocols", Addision Wesley, ISBN 0-201-63346-9
  • Gary R. Wright, W. Richard Stevens: "TCP/IP Illustrated, Volume 2 - The Implementation", Addision Wesley, ISBN 0-201-63354-X
  • W. Richard Stevens: "TCP/IP Illustrated, Volume 3 - TCP for Transactions", Addision Wesley, ISBN 0-201-63495-3
  • W. Richard Stevens: "UNIX Network Programming, Volume 1 - Networking APIs: Sockets and XTI", 2nd ed., Prentice Hall, ISBN-0-13-490012-X
  • W. Richard Stevens: "UNIX Network Programming, Volume 2 - Interprocess Communication", 2nd ed., Prentice Hall, ISBN-0-13-081081-9

12.2.4. PowerPC Programming

12.3. Mailing Lists

These are some mailing lists of interest. If you are new to mailing lists then please take the time to read at least RFC 1855.

  • linuxppc-embedded - Communications among developers and users of Linux on embedded PowerPC?boards
  • linuxppc-dev - Communications among active developers of Linux on 32 bit PowerPC plattforms. Not intended for user support.
  • linuxppc64-dev - Communications among active developers of Linux on 64 bit PowerPC plattforms. Not intended for user support.
  • u-boot-users - Support for "U-Boot" Universal Bootloader
  • u-boot-cvs - This mailing list tracks CVS commits. Not intended for discussions.

12.4. Links

Linux Kernel Resources:

RTAI:

U-Boot:

Cross Development Tools:

Programming:

Standards:

12.5. More Links

12.6. Tools

  • http://lxr.linux.no/source/ - Cross-Referencing the Linux Kernel - using a versatile hypertext cross-referencing tool for the Linux Kernel source tree (the Linux Cross-Reference project)
  • ftp://ftp.denx.de/pub/tools/backtrace - Decode Stack Backtrace - Perl script to decode the Stack Backtrace printed by the Linux Kernel when it panics
  • ftp://ftp.denx.de/pub/tools/clone_tree - "Clone" a Source Tree - Perl script to create a working copy of a source tree (for example the Linux Kernel) which contains mainly symbolic links (and automagically omits "unwanted" files like CVS repository data, etc.) 

; bdiGDB configuration file for TQM8xxL Module
; --------------------------------------------
;
[INIT]
; init core register
WREG    MSR             0x00001002      ;MSR  : ME,RI
WSPR    27              0x00001002      ;SRR1 : ME,RI
WSPR    149             0x2002000F      ;DER  : set debug enable register
;;WSPR  149             0x2006000F      ;DER  : enable SYSIE for BDI flash progr.
WSPR    638             0xFFF00000      ;IMMR : internal memory at 0xFFF00000
WSPR    158             0x00000007      ;ICTRL:
 
; init SIU register
;;;WM32 0xFFF00000      0x00610400      ;SIUMCR
WM32    0xFFF00000      0x00010400      ;SIUMCR - for use with PCMCIA
WM32    0xFFF00004      0xFFFFFF89      ;SYPCR
 
WSPR    796             0x00000000      ;M_TWB: invalidate TWB
 
[TARGET]
MMU         XLAT        ; support virtual addresses (for Linux!)
PTBASE      0x000000F0  ; ptr to page table pointers
CPUCLOCK    45000000    ;the CPU clock rate after processing the init list
BDIMODE     AGENT       ;the BDI working mode (LOADONLY | AGENT)
BREAKMODE   HARD        ;SOFT or HARD, HARD uses PPC hardware breakpoints
                                                                                
[HOST]
IP          192.168.3.1
FILE        /tftpboot/TQM8xxL/u-boot.bin
FORMAT      BIN
LOAD        MANUAL      ;load code MANUAL or AUTO after reset
DEBUGPORT   2001
START       0x0100
                                                                                
[FLASH]
CHIPTYPE    AM29BX16    ;Flash type (AM29LV160B)
CHIPSIZE    0x200000    ;The size of one flash chip in bytes
BUSWIDTH    32          ;The width of the flash memory bus in bits (8 | 16 | 32)
WORKSPACE   0xFFF02000          ; RAM buffer for fast flash programming
FILE        /tftpboot/TQM8xxL/u-boot.bin        ;The file to program
FORMAT      BIN  0x00000000
ERASE       0x00000000 BLOCK
ERASE       0x00008000 BLOCK
ERASE       0x0000C000 BLOCK
ERASE       0x00010000 BLOCK
ERASE       0x00020000 BLOCK
                                                                                
[REGS]
DMM1    0xFFF00000
FILE    /tftpboot/reg860.def
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