On Tue 2016-02-02 16:45:23, Torsten Duwe wrote: > On Tue, Feb 02, 2016 at 01:12:24PM +0100, Petr Mladek wrote: > > > > Hmm, the size of the offset is not a constant. In particular, leaf > > functions do not set TOC before the mcount location. > > To be slightly more precise, a leaf function that additionally uses > no global data. No global function calls, no global data access => > no need to load the TOC. Thanks for explanation. > > The result is that kernel crashes when trying to trace leaf function > > The trampoline *requires* a proper TOC pointer to find the remote function > entry point. If you jump onto the trampoline with the TOC from the caller's > caller you'll grab some address from somewhere and jump into nirvana. The dmesg messages suggested someting like this. > > By other words, it seems that the code generated with -mprofile-kernel > > option has been buggy in all gcc versions. > > Either that or we need bigger trampolines for everybody. > > Michael, should we grow every module trampoline to always load R2, > or fix GCC to recognise the generated bl _mcount as a global function call? > Anton, what do you think? BTW: Is the trampoline used also for classic probes? If not, we might need a trampoline for them as well. Note that TOC is not set only when the problematic functions are compiled with --mprofile-kernel. I still see the TOC stuff when compiling only with -pg. Best Regards, Petr -- 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
