Can I set a breakpoint on 'memory access' in GDB?

What you're looking for is called a watchpoint.

Usage

(gdb) watch foo: watch the value of variable foo

(gdb) watch *(int*)0x12345678: watch the value pointed by an address, casted to whatever type you want

(gdb) watch a*b + c/d: watch an arbitrarily complex expression, valid in the program's native language

Watchpoints are of three kinds:

• watch: gdb will break when a write occurs
• rwatch: gdb will break wnen a read occurs
• awatch: gdb will break in both cases

You may choose the more appropriate for your needs.

For more information, check this out.

watch only breaks on write, rwatch let you break on read, and awatch let you break on read/write.

You can set read watchpoints on memory locations:

gdb$ rwatch *0xfeedface
Hardware read watchpoint 2: *0xfeedface

but one limitation applies to the rwatch and awatch commands; you can't use gdb variables in expressions:

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

So you have to expand them yourself:

gdb$ print $ebx 
$13 = 0x135700
gdb$ rwatch *0x135700+0xec1a04f
Hardware read watchpoint 3: *0x135700 + 0xec1a04f
gdb$ c
Hardware read watchpoint 3: *0x135700 + 0xec1a04f

Value = 0xec34daf
0x9527d6e7 in objc_msgSend ()

Edit: Oh, and by the way. You need either hardware or software support. Software is obviously much slower. To find out if your OS supports hardware watchpoints you can see the can-use-hw-watchpoints environment setting.

gdb$ show can-use-hw-watchpoints
Debugger's willingness to use watchpoint hardware is 1.