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GDB Cheat Sheet

GNU Debugger (GDB) Cheat Sheet

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$ g++ -g source.cpp -o program
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$ gdb program.exe

-g option embeds symbolic debug information into the output file program. This debug info includes:

• Function names

• Variable names and types

• Line numbers in source code

• Mapping between binary instructions and source code

Sample Program to Practice GDB

Source (gdb.cpp)

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#include <iostream>
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using namespace std;
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void f3()
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{
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    int f3_var = 30;
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    cout << f3_var << end;
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}
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void f2()
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{
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    int f2_var = 20;
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    cout << f2_var << end;
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    f3();
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}
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void f1()
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{
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    int f1_var = 10;
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    cout << f1_var << end;
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    f2();
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}
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int main(int argc, char *argv[])
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{
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    int main_var = 50;
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    cout << main_var << endl;
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    f1();
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    return 0;
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}

Compile the program:

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g++ -g gdb.cpp

Attach GDB:

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gdb .\a.exe

Set breakpoints:

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(gdb) break main
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Breakpoint 1 at 0x14000152c: file gdb.cpp, line 26.
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(gdb) b f3
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Breakpoint 2 at 0x140001468: file gdb.cpp, line 6.

View breakpoints:

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(gdb) info breakpoints
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Num     Type           Disp Enb Address            What
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1       breakpoint     keep y   0x000000014000152c in main(int, char**) at gdb.cpp:26
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2       breakpoint     keep y   0x0000000140001468 in f3() at gdb.cpp:6

Run the program:

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(gdb) run
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Starting program: D:\workspace\cpp\a.exe 
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[New Thread 23204.0x21f4]
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[New Thread 23204.0x1ef0]
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[New Thread 23204.0x34e4]
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Thread 1 hit Breakpoint 1, main (argc=1, argv=0xf2080) at gdb.cpp:26
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26              int main_var = 50;

Continue to the next breakpoint:

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(gdb) continue
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Continuing.
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50
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10
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20
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Thread 1 hit Breakpoint 2, f3 () at gdb.cpp:6
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6           int f3_var = 30;

View call stack:

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(gdb) backtrace
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#0  f3 () at gdb.cpp:6
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#1  0x00007ff677a314d2 in f2 () at gdb.cpp:14
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#2  0x00007ff677a31511 in f1 () at gdb.cpp:21
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#3  0x00007ff677a3155c in main (argc=1, argv=0xf2080) at gdb.cpp:28

#n refers to each stack frame number.

View local variables:

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(gdb) info locals
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f3_var = 0

View the value of a local variable in a different stack frame:

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(gdb) frame 2
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#2  0x00007ff677a31511 in f1 () at gdb.cpp:21
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21          f2();
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(gdb) print f1_var
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$1 = 10

First, you need to go to the stack frame in which the variable you want to print is declared.

View the source code near the current line:

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(gdb) list
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17      void f1()
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18      {
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19          int f1_var = 10;
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20          cout << f1_var << endl;
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21          f2();
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22      }
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24      int main(int argc, char *argv[])
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25      {

View the current line:

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(gdb) frame
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#2  0x00007ff677a31511 in f1 () at gdb.cpp:21
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21          f2();

Return to the top stack frame:

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(gdb) f 0 
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#0  f3 () at gdb.cpp:6
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6           int f3_var = 30;

Run until the current function returns:

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(gdb) finish
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Run till exit from #0  f3 () at gdb.cpp:6
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30[New Thread 23204.0x2738]
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f2 () at gdb.cpp:15
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15      }