On Tue, 14 Jan 2025 15:02:37 +0100 Jiri Olsa <jolsa@xxxxxxxxxx> wrote: > hi, > while checking on similar code for uprobes I was wondering if we > can merge first 2 steps of instruction update in text_poke_bp_batch > function. > > Basically the first step now would be to write int3 byte together > with the rest of the bytes of the new instruction instead of doing > that separately. And the second step would be to overwrite int3 > byte with first byte of the new instruction. > > Would that work or do I miss some x86 detail that could lead to crash? I agree with Peterz and David. My original idea is that the putting int3 is safe anyway because it is just 1 byte. Then we can update following bytes (only after we ensure no one executing(e.g. interrupted) that part). The another good point of int3 is that can avoid writing over cache-line boundary because it is 1 byte. Without this int3 detour, it is possible to see half-way updated instruction from some other CPU cores :( Thank you, -- Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
