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(Created page with '== References == * [http://www.unknownroad.com/rtfm/gdbtut/gdbsegfault.html 7.2 Example Debugging Session: Segmentation Fault Example] * == Compile with debug symbols == * Opti…') |
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<source lang="bash"> |
<source lang="bash"> |
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gcc -g program.c # -g : debug symbols |
gcc -g program.c # -g : debug symbols |
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</source> |
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== GDB invocation == |
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<source lang="bash"> |
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gdb a.out |
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gdb a.out core.1234 |
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</source> |
</source> |
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;next |
;next |
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:Step to next instruction |
:Step to next instruction |
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== GDB examples == |
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=== Simple Segmentation Fault Example === |
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(From [http://www.unknownroad.com/rtfm/gdbtut/gdbsegfault.html]) |
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{| class="wikitable" width=100% |
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|- |
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|width=50%|Example program <tt>segfault.c</tt>: |
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<source lang="c"> |
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#include <stdio.h> |
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#include <stdlib.h> |
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int main(int argc, char **argv) |
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{ |
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char *buf; |
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buf = malloc(1<<31); |
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fgets(buf, 1024, stdin); |
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printf("%s\n", buf); |
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return 1; |
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} |
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</source> |
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|Compile and launch gdb: |
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<source lang="bash"> |
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gcc -g segfault.c |
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gdb a.out |
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</source> |
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The debug session |
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<source lang="gdb"> |
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run |
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backtrace |
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frame 3 |
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print buf |
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kill |
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break segfault.c:8 |
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run |
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print buf |
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next |
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print buf |
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</source> |
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Revision as of 11:03, 22 July 2011
References
Compile with debug symbols
- Option -g:
gcc -g program.c # -g : debug symbols
GDB invocation
gdb a.out
gdb a.out core.1234
GDB commands
- help
- Get help on commands
- run [ARGS]
- Start debugged program. Arguments may include wildcards (*) and redirections (<, <<...)
- backtrace [COUNT]
- bt [COUNT]
- where [COUNT]
- Print backtrace of all stack frames, or innermost (outermost) COUNT frames if COUNT>0 (COUNT<0)
- frame [FRAME]
- Select and print stack frame
- print VAR
- Print value of variable VAR
- kill
- Kill current program
- break FILELINE
- Insert a breakpoint at file FILE, line LINE
- next
- Step to next instruction
GDB examples
Simple Segmentation Fault Example
(From [1])
Example program segfault.c:
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char **argv)
{
char *buf;
buf = malloc(1<<31);
fgets(buf, 1024, stdin);
printf("%s\n", buf);
return 1;
}
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Compile and launch gdb:
gcc -g segfault.c
gdb a.out
The debug session run
backtrace
frame 3
print buf
kill
break segfault.c:8
run
print buf
next
print buf |