Using gdb to convert addresses to lines

When using GDB for debugging, it is frequently necessary to map specific memory addresses to line numbers in the source code. This capability is particularly useful when analyzing program crashes, for example, when you obtain a stack trace, which typically provides only memory addresses rather than source code line information. Below, I will detail how to convert addresses to their corresponding source code lines within GDB.

Steps

1. Start GDB: Ensure your program was compiled with debugging symbols. This usually requires adding the -g flag during compilation. For instance, for a C or C++ program, the compilation command could be:

bash
 gcc -g myprogram.c -o myprogram

1. Load the program into GDB:

bash
 gdb ./myprogram

1. Use the list command: In GDB, you can use the list command to associate a specific address with a line in the source code. The syntax is:

gdb
 list *address

For example, to locate the line for address 0x4005d4:

gdb
 list *0x4005d4

Example

Assume we are debugging a simple program that crashes due to an error in a function. When the error occurs, the stack trace obtained from GDB appears as:

shell
Program received signal SIGSEGV, Segmentation fault.
0x00000000004005d4 in mystery_function () at example.c:8

Here, 0x00000000004005d4 represents the program counter address at the crash point. To find the corresponding source code line in GDB, proceed as follows:

1. Launch GDB and load the program:

bash
 gdb ./myprogram

1. Enter the command to locate the address:

gdb
 list *0x4005d4

GDB will output information similar to the following, showing the corresponding line in the source code:

shell
8       int x = *nullptr;  // The statement causing the crash

Conclusion

Using the list *address command effectively assists developers in mapping addresses back to specific lines in the source code, which is essential for debugging and understanding program behavior. This approach proves particularly valuable when handling complex programs or investigating unexpected crashes.