On Fri, Oct 06, 2017 at 11:27:42AM +0530, Kamalesh Babulal wrote: > > Consider the livepatch sequence[1]. Where function A calls B, B is the > function which has been livepatched and the call to function B is > redirected to patched version P. P calls the function C in M2, whereas > C was local to the function B and have became SHN_UNDEF in function P. > Local call becoming global. > > +--------+ +--------+ +--------+ +--------+ > | | +--------+--------+--->| | +-->| | > | A | | | B | | F | | | P | > | | | | | | +--+ | | > | +---+ | | | |<-+ | | > | |<--+ +----+ C | | | | | | > | | | | +->| | | | | | |<---+ > | K / M1 | | | | | K / M2 | +-+ Kernel | +---+ Mod3 +--+ | > +--------+ | | | +--------+ | +--------+ +--------+ | | > | | | | | | > +---+-+--------------+ | | > | | | | > | +--------------------------------------------+ | > +------------------------------------------------+ > > > Handling such call with regular stub, triggers another error: > > module_64: kpatch_meminfo: Expect noop after relocate, got 3d220000 > > Every branch to SHN_UNDEF is followed by a nop instruction, that gets > overwritten by an instruction to restore TOC with r2 value that get > stored onto the stack, before calling the function via global entry > point. > > Given that C was local to function B, it does not store/restore TOC as > they are not expected to be clobbered for functions called via local > entry point. Can you please provide example source code of Mod3 and C? If P calls C, this is a regular global call, the TOC is saved by the stub and restored after the call instruction. Why do you think this is not the case? Torsten -- 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
