How Can I Monitor Variable Access and Memory Reads/Writes in GDB Using Breakpoints?

Monitoring Variable Access in GDB: Breakpoints on 'Memory Access'

In GDB, you can set breakpoints to monitor specific variables and identify when they are accessed or modified. Here's a breakdown of GDB commands and techniques for this purpose:

Watchpoint Commands:

• watch: Breaks on variable writes
• rwatch: Breaks on variable reads
• awatch: Breaks on variable reads/writes

Setting Watchpoints on Memory Locations:

You can set watchpoints on memory locations using the rwatch command:

gdb$ rwatch *0xfeedface

This will trigger a breakpoint whenever the memory address 0xfeedface is read.

Limitations of Watchpoints on Expressions:

Note that GDB watchpoints cannot be set on expressions involving variables:

gdb$ rwatch $ebx+0xec1a04f
Expression cannot be implemented with read/access watchpoint.

To work around this, manually expand the expression:

gdb$ print $ebx
 = 0x135700
gdb$ rwatch *0x135700+0xec1a04f

Hardware vs. Software Support:

Hardware watchpoints offer faster performance than software watchpoints. To check if your OS supports hardware watchpoints, run the following command:

gdb$ show can-use-hw-watchpoints

If the output is 1, hardware watchpoints are available.

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