X86 debug registers (DR0-3, DR6, DR7) are also useful. They don't require code changes. As an added bonus, you can set a breakpoint for a variable access, which

X86 debug registers (DR0-3, DR6, DR7) are also useful. They don't require code changes. As an added bonus, you can set a breakpoint for a variable access, which triggers whenever a certain variable is accessed. Although unfortunately debug registers are limited to just 4 simultaneous breakpoints in the same time. http://wiki.osdev.org/CPU_Registers_x86#Debug_Registers http://wiki.osdev.org/CPU_Registers_x86#Debug_Registers