On Thu, Mar 31, 2016 at 7:14 PM, Mark Rutland <mark.rutl...@arm.com> wrote: > On Thu, Mar 31, 2016 at 06:33:24PM +0200, Alexander Potapenko wrote: >> On Thu, Mar 31, 2016 at 6:00 PM, Mark Rutland <mark.rutl...@arm.com> wrote: >> > On Thu, Mar 31, 2016 at 05:09:29PM +0200, Alexander Potapenko wrote: >> >> Currently kcov instrumentation is disabled for the following files: >> > >> >> arch/x86/boot/* >> >> arch/x86/boot/compressed/* >> >> arch/x86/entry/vdso/* >> >> arch/x86/realmode/rm/* >> > >> > These are executed outside of the usual kernel context / address space, >> > so excluding these makes sense to me. >> > >> >> arch/x86/kernel/* >> >> arch/x86/kernel/apic/* >> >> arch/x86/kernel/cpu/common.c >> >> arch/x86/kernel/cpu/perf_event.c >> >> arch/x86/lib/delay.c >> >> arch/x86/mm/tlb.c >> > >> > For these, it's not immediately clear to me why instrumentation is >> > disabled, so I don't know whether or not we can instrument the analogous >> > arm64 code. >> According to the comments in >> https://github.com/torvalds/linux/commit/5c9a8750a6409c63a0f01d51a9024861022f6593, >> instrumentation of arch/x86/kernel/apic/* and arch/x86/lib/delay.c >> leads to non-deterministic coverage, > > To what extent does determinism matter? Are we just ruling out the worst > cases, or is this likely to turn into a whack-a-mole game? I guess we'd better ask Dmitry who excluded these files on x86 and experimented with coverage a lot. Dmitry, can you clarify this, please? > Do we exclude clocksources and other driver code? > > Looking at the arm64 delay timer code, it looks like everything will be > inlined (and therefore coverage should be deterministic so long as the > delay functions are called deterministically). That said, the same looks > basically true of the x86 code, so I guess I've misunderstood. > >> instrumenting others prevent the kernel from booting. > > I haven't been able to come up with a scenario whereby kcov would be > fatal for the above, so it's difficult to say if we have equivalent > problems. > > For reference, do we have any examples as to why any of these prevent > booting? Not sure there's any documentation so far except for the comments in the original kcov patch.
>> >> Only a handful of the above have corresponding files in arch/arm64: >> >> arch/arm64/boot/* >> >> arch/arm64/kernel/* >> >> arch/arm64/lib/delay.c >> > >> > We have arch/arm64/kernel/perf_event.c, and a couple of other files that >> > are directly analogous, even if the paths don't quite line up. >> Ok, it makes sense to also disable arch/arm64/kernel/perf_event.c then. > > Potentially, though it really depends on why it was excluded on x86. > > Some of the arm64 perf code lives in drivers/perf/arm_pmu.c, also. > > Thanks, > Mark. -- Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Straße, 33 80636 München Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg