On Fri, Mar 09, 2018 at 05:47:18PM +0100, Torsten Duwe wrote: > On Thu, 8 Mar 2018 10:26:16 -0600 > Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote: > > > This doesn't seem to address some of my previous concerns: > > You're right. That discussion quickly headed towards objtool > and I forgot about this one paragraph with the remarks. > > > - Bailing on interrupt/exception frames > > That is a good question. My current code keeps unwinding as long > as the trace looks sane. If the exception frame has a valid code > pointer in the LR slot it will continue. Couldn't there be cases > where this is desirable? I thought we established in the previous discussion that this could cause some functions to get skipped in the stack trace: https://lkml.kernel.org/r/20171219214652.u7qeb7fxov62ttke@treble > Should this be configurable? Not that > I have an idea how this situation could occur for a thread > that is current or sleeping... Page faults and preemption. > Michael, Balbir: is that possible? Any Idea how to reliably detect > an exception frame? My approach would be to look at the next return > address and compare it to the usual suspects (i.e. collect all > "b ret" addresses in the EXCEPTION_COMMON macro, for BookS). It looks like show_stack() already knows how to do this: /* * See if this is an exception frame. * We look for the "regshere" marker in the current frame. */ if (validate_sp(sp, tsk, STACK_INT_FRAME_SIZE) && stack[STACK_FRAME_MARKER] == STACK_FRAME_REGS_MARKER) { So you could do something similar. > > - Function graph tracing return address conversion > > > > - kretprobes return address conversion > > You mean like in arch/x86/kernel/unwind_frame.c the call to > ftrace_graph_ret_addr ? > > Forgive me my directness but I don't see why these should be handled in > arch-dependent code, other than maybe a hook, if inevitable, that calls > back into the graph tracer / kretprobes in order to get the proper > address, I don't really follow, where exactly would you propose calling ftrace_graph_ret_addr() from? > or simply call the trace unreliable in case it finds such a > return address. If you're going to make livepatch incompatible with function graph tracing, there needs to be a good justification for it (and we'd need to make sure existing users are fine with it). -- Josh -- To unsubscribe from this list: send the line "unsubscribe live-patching" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
