Not printf exactly, but I've found bugs with a combination of mprotect, userfaultfd and backtrace_symbols when I couldn't use HW breakpoints.
Basically, mark a set of pages as non-writable so that any writes trigger a pagefault, then register yourself as a pagefault handler for those and see who is doing the write, apply the write and move on. You can do this with LD_PRELOAD without even recompiling the debugee.
Not printf exactly, but I've found bugs with a combination of mprotect, userfaultfd and backtrace_symbols when I couldn't use HW breakpoints.
Basically, mark a set of pages as non-writable so that any writes trigger a pagefault, then register yourself as a pagefault handler for those and see who is doing the write, apply the write and move on. You can do this with LD_PRELOAD without even recompiling the debugee.