As I mentioned earlier this year, it's a bad idea to call _mcount from MMU helper functions (e.g. hash_page...), when the profiling/tracing/ live-patching/whatever framewok might in turn cause another such fault. Jikos suggested to use fine-grained control of these functions with the "notrace" keyword in the Linux kernel. It is mapped to GCC's (4.8, FWIW) __attribute__((no_instrument_function)), which, to my surprise, works for -p and -pg nicely, but does not affect -mprofile-kernel at all! Should we consider this a bug? IMHO it is. I can see in the GCC sources that -mprofile-kernel is more like a low-level hack in rs6000.c, quite far below the RTL code generator, so the no_instrument_function attribute is probably hard to check for. What is -mprofile-kernel good for, if it bears such a risk of crashing the kernel? Is it the right hook for ppc64 live patching? How to protect those critical functions? Filter -mprofile-kernel for those object files? Ask the GCC experts to fix this? Any ideas welcome! 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
