On Sat, Sep 26, 2015 at 04:30:08PM +0200, Torsten Duwe wrote: > 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! That is surprising; please file a GCC bug. > 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? It didn't work when combined with other fringe functionality. It happens. > Is it the right hook for ppc64 live patching? How to protect > those critical functions? Filter -mprofile-kernel for those object files? That might work. > Ask the GCC experts to fix this? Yes please. You probably need a workaround for released compilers though. Segher -- 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
