On Wed, Aug 30, 2017 at 8:23 PM, Mark Rutland <mark.rutl...@arm.com> wrote: > Hi, > > On Wed, Aug 30, 2017 at 06:23:29PM +0200, Dmitry Vyukov wrote: >> From: Victor Chibotaru <tch...@google.com> >> >> Enables kcov to collect comparison operands from instrumented code. >> This is done by using Clang's -fsanitize=trace-cmp instrumentation >> (currently not available for GCC). > > What's needed to build the kernel with Clang these days? > > I was under the impression that it still wasn't possible to build arm64 > with clang due to a number of missing features (e.g. the %a assembler > output template). > >> The comparison operands help a lot in fuzz testing. E.g. they are >> used in Syzkaller to cover the interiors of conditional statements >> with way less attempts and thus make previously unreachable code >> reachable. >> >> To allow separate collection of coverage and comparison operands two >> different work modes are implemented. Mode selection is now done via >> a KCOV_ENABLE ioctl call with corresponding argument value. >> >> Signed-off-by: Victor Chibotaru <tch...@google.com> >> Cc: Andrew Morton <a...@linux-foundation.org> >> Cc: Mark Rutland <mark.rutl...@arm.com> >> Cc: Alexander Popov <alex.po...@linux.com> >> Cc: Andrey Ryabinin <aryabi...@virtuozzo.com> >> Cc: Kees Cook <keesc...@chromium.org> >> Cc: Vegard Nossum <vegard.nos...@oracle.com> >> Cc: Quentin Casasnovas <quentin.casasno...@oracle.com> >> Cc: syzkal...@googlegroups.com >> Cc: linux...@kvack.org >> Cc: linux-kernel@vger.kernel.org >> --- >> Clang instrumentation: >> https://clang.llvm.org/docs/SanitizerCoverage.html#tracing-data-flow > > How stable is this? > > The comment at the end says "This interface is a subject to change."
The intention is that this is not subject to change anymore (since we are using it in kernel). I've mailed change to docs: https://reviews.llvm.org/D37303 FWIW, there is patch in flight that adds this instrumentation to gcc: https://groups.google.com/forum/#!topic/syzkaller/CSLynn6nI-A It seems to be stalled on review phase, though.
