Q.
Can you provide some quick GDB commands for a newbie?
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A.
This is a quick FAQ written in a typical debug sequence and is only meant for beginners. I just extracted the contents of the uploaded file in Doc Site:
http://docs.blackfin.uclinux.org/lib/exe/fetch.php?media=presentations:toolchain:gdb_for_dummies.pdf
Fact Sheet
What is GDB? http://shop.fsf.org/product/debugging-gdb-gnu-source-level-debugger/
“GDB, the GNU Project debugger, allows you to see what is going on `inside' another program while it executes -- or what another program was doing at the moment it crashed. GDB can do four main kinds of things (plus other things in support of these) to help you catch bugs in the act:
- Start your program, specifying anything that might affect its behavior.
- Make your program stop on specified conditions.
- Examine what has happened, when your program has stopped.
- Change things in your program, so you can experiment with correcting the effects of one bug and go on to learn about another. ”
What is GDB Server? http://en.wikipedia.org/wiki/Gdbserver
“gdb-server is a computer program that makes it possible to remotely debug other programs.Running on the same system as the program to be debugged, it allows the GNU Debugger to connect from another system; that is, only the executable to be debugged needs to be resident on the target system, while the source code and a copy of the binary file to be debugged reside on the developer’s local computer. The connection can be either TCP or a serial line”
What is GDB Proxy? https://docs.blackfin.uclinux.org/doku.php?id=toolchain:debug:gdbproxy
When debugging under the gdb environment, the debugger needs to know what target to connect to. This target is a tiny server daemon, typically running on the host computer. It is equivalent to a gdbserver, although it does not run on the target hardware. This server is called gdbproxy and is derived from rproxy-0.7.
What is Eclipse? http://en.wikipedia.org/wiki/Eclipse_(software)
Eclipse is a multi-language software development environment comprising an integrated development environment (IDE) and an extensible plug-in system. It is written mostly in Java and can be used to develop applications in Java and, by means of various plug-ins, other programming languages including Ada, C, C++, COBOL, Perl, PHP, Python, R. Ruby (including Ruby on Rails framework), Scala, Clojure, and Scheme.
What is GDB/mi Interface? http://sourceware.org/gdb/onlinedocs/gdb/GDB_002fMI.html#GDB_002fMI
GDB/MI is a line based machine oriented text interface to GDB and is activated by specifying using the --interpreter command line option (see Mode Options). It is specifically intended to support the development of systems which use the debugger as just one small component as a larger system {Eclipse}.
Lets learn from a simple no-hardware code as below. All following gdb commands are sequentially tested…
| Sample code for debugging |
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int global_data = 1111; void func1(); void func2(); int main(void); int main(void) { func1(); return 0; } void func1() { int local_data = 1234; global_data = 5678; func2(); } void func2() { } |
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Start the GDB first: |
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C:\Program Files\Analog Devices\GNU Toolchain\2010R1\elf\bin>bfin-elf-gdb.exe gdb_debugging GNU gdb 6.6 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 "--host=i386-mingw32msvc --target=bfin-elf"... (gdb) target remote localhost:2000 Remote debugging using localhost:2000 main () at ../src/gdb_debugging.c:9 9 func1(); (gdb) load Loading section .rodata, size 0x8 lma 0xff800000 Loading section .eh_frame, size 0x4 lma 0xff800008 Loading section .ctors, size 0x8 lma 0xff80000c Loading section .dtors, size 0x8 lma 0xff800014 Loading section .jcr, size 0x4 lma 0xff80001c Loading section .data, size 0x40c lma 0xff800020 Loading section .text, size 0x510 lma 0xffa00000 Loading section .init, size 0x12 lma 0xffa00510 Loading section .fini, size 0xe lma 0xffa00522 Start address 0xffa00000, load size 2396 Transfer rate: 140941 bits/sec, 266 bytes/write. |
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Insert some break points – at the entry of each function: |
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(gdb) break main Breakpoint 1 at 0xffa00274: file ../src/gdb_debugging.c, line 9. (gdb) break func1 Breakpoint 2 at 0xffa00284: file ../src/gdb_debugging.c, line 17. (gdb) break func2 Breakpoint 3 at 0xffa002ac: file ../src/gdb_debugging.c, line 28. |
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Run the code and it should hit breakpoints. |
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(gdb) continue Continuing. Breakpoint 1, main () at ../src/gdb_debugging.c:9 9 func1(); (gdb) continue Continuing. Breakpoint 2, func1 () at ../src/gdb_debugging.c:17 17 int local_data = 1234; |
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Let’s play with breakpoints. See the information of the breakpoints, how it can be disabled. |
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(gdb) info breakpoints Num Type Disp Enb Address What 1 breakpoint keep y 0xffa00274 in main at ../src/gdb_debugging.c:9 breakpoint already hit 1 time 2 breakpoint keep y 0xffa00284 in func1 at ../src/gdb_debugging.c:17 breakpoint already hit 1 time 3 breakpoint keep y 0xffa002ac in func2 at ../src/gdb_debugging.c:28 (gdb) disable 2 (gdb) info breakpoints Num Type Disp Enb Address What 1 breakpoint keep y 0xffa00274 in main at ../src/gdb_debugging.c:9 breakpoint already hit 1 time 2 breakpoint keep n 0xffa00284 in func1 at ../src/gdb_debugging.c:17 breakpoint already hit 1 time 3 breakpoint keep y 0xffa002ac in func2 at ../src/gdb_debugging.c:28 |
| Where are we now? |
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| gdb) where
#0 func1 () at ../src/gdb_debugging.c:17 #1 0xffa00278 in main () at ../src/gdb_debugging.c:9 |
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Single stepping the code… |
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(gdb) step 19 global_data = 5678; |
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Let’s print the local variable.. |
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(gdb) info local local_data = 1234 |
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And the global variable… |
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(gdb) print/x global_data $1 = 0x457 |
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Check out the dis-assembly |
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(gdb) disassemble 0xffa00280 0xffa002a0 Dump of assembler code from 0xffa00280 to 0xffa002a0: 0xffa00280 <func1+0>: LINK 0x10; /* (16) */ 0xffa00284 <func1+4>: R0 = 0x4d2 (X); /* R0=0x0x4d2(1234) */ 0xffa00288 <func1+8>: [FP -0x4] = R0; 0xffa0028a <func1+10>: P2.H = 0xff80; /* (-128) P2=0x0xff800000<_global_impure_ptr> */ 0xffa0028e <func1+14>: P2.L = 0x24; /* ( 36) P2=0x0xff800024<global_data> */ 0xffa00292 <func1+18>: R0 = 0x162e (X); /* R0=0x0x162e(5678) */ 0xffa00296 <func1+22>: [P2] = R0; 0xffa00298 <func1+24>: CALL 0x0xffa002a4 <func2>; 0xffa0029c <func1+28>: UNLINK; End of assembler dump. |
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We run again… |
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(gdb) continue Continuing. Breakpoint 3, func2 () at ../src/gdb_debugging.c:28 28 } |
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Look at the back-trace info of function calls and frame info. |
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(gdb) bt #0 func2 () at ../src/gdb_debugging.c:28 #1 0xffa0029c in func1 () at ../src/gdb_debugging.c:21 #2 0xffa00278 in main () at ../src/gdb_debugging.c:9 (gdb) backtrace full #0 func2 () at ../src/gdb_debugging.c:28 No locals. #1 0xffa0029c in func1 () at ../src/gdb_debugging.c:21 local_data = 1234 #2 0xffa00278 in main () at ../src/gdb_debugging.c:9 No locals. (gdb) frame #0 func2 () at ../src/gdb_debugging.c:28 28 } |
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Core register information... |
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(gdb) info registers r0 0x162e 5678 r1 0xff80042c -8387540 r2 0x0 0A r3 0x0 0 r4 0x8000 32768 r5 0x989680 10000000 r6 0x0 0 r7 0x0 0 p0 0xff800178 0xff800178 p1 0x1 0x1 p2 0xff800024 0xff800024 p3 0x3f1ff80 0x3f1ff80 p4 0x3f22148 0x3f22148 p5 0xffc03060 0xffc03060 sp 0xffb00f9c 0xffb00f9c fp 0xffb00f9c 0xffb00f9c i0 0xffe01300 -2092288 i1 0xffe00300 -2096384 i2 0x7d801048 2105544776 i3 0x7f900840 2140145728 m0 0x0 0 m1 0x0 0 m2 0xff807ffc -8355844 m3 0x0 0 b0 0x7fa7e73e 2141710142 b1 0xb5025ff6 -1258135562 b2 0x5b4597f7 1531287543 b3 0x4c3dac51 1279110225 l0 0x0 0 l1 0x0 0 l2 0x0 0 l3 0x0 0 a0x 0x0 0 a0w 0x3200000 52428800 a1x 0x0 0 a1w 0x2b53 11091 astat 0x2001025 33558565 rets 0xffa0029c 0xffa0029c <func1+28> lc0 0x0 0 lt0 0xffa0005c -6291364 lb0 0xffa0005d -6291363 lc1 0x0 0 lt1 0xffa00366 -6290586 lb1 0xffa00367 -6290585 cycles 0xa07d46a4 -1602402652 cycles2 0x0 0 usp 0xffb00ff4 0xffb00ff4 seqstat 0x0 0 syscfg 0x32 50 reti 0xffa000e8 -6291224 retx 0xffa004d6 -6290218 retn 0x986b21f 159822367 rete 0xffa002ac -6290772 pc 0xffa002ac 0xffa002ac <func2+8> cc 0x1 1 text_addr 0x0 0 text_end_addr 0x0 0 data_addr 0x0 0 fdpic_exec 0x0 0 fdpic_interp 0x0 0 ipend 0x0 0 |
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Set some global data |
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(gdb) set global_data = 9999 (gdb) print global_data $2 = 9999 |
GDB/MI interface is meant for IDDE such as Eclipse. There are of course some simple useful commands. But beware – the console out seems terribly bad, when these commands are invoked directly.
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Setting up as usual. |
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C:\Program Files\Analog Devices\GNU Toolchain\2010R1\elf\bin>bfin-elf-gdb.exe --interpreter=mi gdb_debugging ~"GNU gdb 6.6\n" ~"Copyright (C) 2006 Free Software Foundation, Inc.\n" ~"GDB is free software, covered by the GNU General Public License, and you are\n" ~"welcome to change it and/or distribute copies of it under certain conditions.\n" ~"Type \"show copying\" to see the conditions.\n" ~"There is absolutely no warranty for GDB. Type \"show warranty\" for details.\n" ~"This GDB was configured as \"--host=i386-mingw32msvc --target=bfin-elf\"...\n" (gdb) target remote localhost:2000 &"target remote localhost:2000\n" ~"Remote debugging using localhost:2000\n" ~"main () at ../src/gdb_debugging.c:9\n" ~"9\t\tfunc1();\n" ^done |
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Dis-assembly |
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(gdb) -data-disassemble -f gdb_debugging.c -l 15 -n 3 -- 0 ^done,asm_insns= [{address="0xffa00280",func-name="func1",offset="0",inst="LINK 0x10;\t\t/* (16) */"}, {address="0xffa00284",func-name="func1",offset="4",inst="R0 = 0x4d2 (X);\t\t/*\t\tR0=0x0x4d2(1234) */"}, {address="0xffa00288",func-name="func1",offset="8",inst="[FP -0x4] = R0;"}] |
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Reading and writing data |
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(gdb) -data-read-memory 0xff800000 x 1 3 3 ^done,addr="0xff800000",nr-bytes="9",total-bytes="9",next-row="0xff800003",prev-row="0xff7ffffd",next-page="0xff800009",prev-page="0xff7ffff7", memory=[{addr="0xff800000",data=["0x00","0x00","0x00"]}, {addr="0xff800003",data=["0x00","0x43","0x00"]}, {addr="0xff800006",data=["0x00","0x00","0xff"]}] (gdb) -data-write-memory 0xff800000 x 1 0x11 ^done (gdb) -data-write-memory 0xff800001 x 1 0x22 ^done (gdb) -data-write-memory 0xff800001 x 1 0x33 ^done (gdb) -data-read-memory 0xff800000 x 1 3 3 ^done,addr="0xff800000",nr-bytes="9",total-bytes="9",next-row="0xff800003",prev-row="0xff7ffffd",next-page="0xff800009",prev-page="0xff7ffff7", memory=[{addr="0xff800000",data=["0x11","0x33","0x00"]}, {addr="0xff800003",data=["0x00","0x43","0x00"]}, {addr="0xff800006",data=["0x00","0x00","0xff"]}] (gdb) |