Messages in this thread Patch in this message | | | Date | Thu, 31 Mar 2016 17:09:29 +0200 | Subject | Re: [PATCH v1] arm64: allow building with kcov coverage on ARM64 | From | Alexander Potapenko <> |
| |
On Thu, Mar 31, 2016 at 4:29 PM, Mark Rutland <mark.rutland@arm.com> wrote: > Hi, > > On Thu, Mar 31, 2016 at 03:54:45PM +0200, Alexander Potapenko wrote: >> Add ARCH_HAS_KCOV to ARM64 config. Disable instrumentation of >> arch/arm64/lib/delay.c > > Why do we disable instrumentation of delay.c? The main purpose of kcov is collecting coverage from syscalls. As far as I understand, coverage of functions from delay.c doesn't deterministically depend on the syscalls being called and their arguments. The initial kcov implementation (https://github.com/torvalds/linux/commit/5c9a8750a6409c63a0f01d51a9024861022f6593) disabled instrumentation of arch/x86/lib/delay.c, so I just copied that chunk.
> What exactly does kcov instrumentation imply? Does it require certain > data to be mapped or certain functions to be callable while instrumented > functions are called? Yes, there is __sanitizer_cov_trace_pc() that must be callable. At boot time |current->kcov_mode| zero, so it virtually does nothing.
Currently kcov instrumentation is disabled for the following files:
arch/x86/boot/* arch/x86/boot/compressed/* arch/x86/entry/vdso/* 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 arch/x86/realmode/rm/*
Only a handful of the above have corresponding files in arch/arm64: arch/arm64/boot/* arch/arm64/kernel/* arch/arm64/lib/delay.c
My patch explicitly disables instrumentation for arch/arm64/lib/delay.c. I never had problems with arch/arm64/boot/* and arch/arm64/kernel/* in the 3.18 kernel, although instrumentation of the corresponding x86 code is claimed to cause boot-time hangs. We can act conservatively and still disable instrumentation for these two dirs just to make sure nothing breaks in the future.
> We have some C code that is run outside of the normal kernel context > (e.g. EFI stub, KVM hyp code), and I suspect it may be necessary to > disable instrumentation for those also. EFI stub and a number of other files is already disabled by the initial kcov patch. I understand there might be some code specific to ARM64 that I may have overlooked, so I'd be grateful if someone could try the patch out with the upstream kernel.
WBR, Alex
> Thanks, > Mark. > >> Signed-off-by: Alexander Potapenko <glider@google.com> >> --- >> arch/arm64/Kconfig | 1 + >> arch/arm64/lib/Makefile | 3 +++ >> 2 files changed, 4 insertions(+) >> >> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig >> index 4f43622..c52aa61 100644 >> --- a/arch/arm64/Kconfig >> +++ b/arch/arm64/Kconfig >> @@ -7,6 +7,7 @@ config ARM64 >> select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE >> select ARCH_HAS_ELF_RANDOMIZE >> select ARCH_HAS_GCOV_PROFILE_ALL >> + select ARCH_HAS_KCOV >> select ARCH_HAS_SG_CHAIN >> select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST >> select ARCH_USE_CMPXCHG_LOCKREF >> diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile >> index c86b790..b407bc1 100644 >> --- a/arch/arm64/lib/Makefile >> +++ b/arch/arm64/lib/Makefile >> @@ -1,3 +1,6 @@ >> +# Produces uninteresting flaky coverage. >> +KCOV_INSTRUMENT_delay.o := n >> + >> lib-y := bitops.o clear_user.o delay.o copy_from_user.o \ >> copy_to_user.o copy_in_user.o copy_page.o \ >> clear_page.o memchr.o memcpy.o memmove.o memset.o \ >> -- >> 2.8.0.rc3.226.g39d4020 >> >> >> _______________________________________________ >> linux-arm-kernel mailing list >> linux-arm-kernel@lists.infradead.org >> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >>
-- 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
| |