Break anywhere when $r1 equals to string GDB

Question

Is there anyway to break on gdb where $r1 equals to a certain string I know there is :

break [addr] if ((int)strcmp($r1, "hello")) == 0

But what to set in addr when I just wanna break when the r1 is "hello" no matter the address?

Answer 1

Python api in GDB is very convenient to script such solutions. Although the api is a little "wild", I refer to pwndbg on how to use the api. I wrote the following for x86_64 to break only when the first param matches "pol". Full code here

import gdb

class MyBreakpoint (gdb.Breakpoint):
    def stop (self):
        rdi = int(gdb.parse_and_eval("$rdi").cast(gdb.lookup_type('uint64_t')))
        print("x(%x)" % (rdi)), 
        result = gdb.selected_inferior().read_memory(rdi, 10)
        if b'\x00' in result:
            result = bytearray(result).split(b'\x00')[0]
        if result == b'pol':
            return True
        return False

MyBreakpoint("x")