On Thu, May 01, 2014 at 01:45:33PM -0700, Andi Kleen wrote: > Josh Poimboeuf <jpoim...@redhat.com> writes: > > > > kpatch checks the backtraces of all tasks in stop_machine() to ensure > > that no instances of the old function are running when the new function > > is applied. > > How does that work for tail calls? > > call foo > foo: > ... > jmp bar > > bar: > ... code executing ... > > When you backtrace you will see foo, but you are running in bar.
> Note that tail calls can be indirect, so they cannot be resolved > statically. > > CONFIG_DEBUG_INFO usually disables tail calls, but not supporting > it would seem like a large limitation, as the cost can be high. > > It wouldn't surprise me if there are some similar special cases that > can even happen with them disabled. > > In theory you could read LBRs, but even that may miss some extreme > cases. When bar returns, would it skip foo and go straight back to foo's caller? If so, then it should be safe to patch foo after it jumps to bar. -- Josh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
