Stack unwinding produces large amounts of uninteresting coverage.
It's called from KASAN kmalloc/kfree hooks, fault injection, etc.
It's not particularly useful and is not a function of system call args.
Ignore that code.
Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: syzkaller@googlegroups.com
---
arch/x86/kernel/Makefile | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 20a0dd51700a..cd49ebfae984 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -39,6 +39,14 @@ KMSAN_SANITIZE_sev.o := n
# first second.
KCOV_INSTRUMENT_head$(BITS).o := n
KCOV_INSTRUMENT_sev.o := n
+# These are called from save_stack_trace() on debug paths,
+# and produce large amounts of uninteresting coverage.
+KCOV_INSTRUMENT_stacktrace.o := n
+KCOV_INSTRUMENT_dumpstack.o := n
+KCOV_INSTRUMENT_dumpstack_$(BITS).o := n
+KCOV_INSTRUMENT_unwind_orc.o := n
+KCOV_INSTRUMENT_unwind_frame.o := n
+KCOV_INSTRUMENT_unwind_guess.o := n
CFLAGS_irq.o := -I $(src)/../include/asm/trace
--
2.45.2.505.gda0bf45e8d-googOn Tue, Jun 11, 2024 at 09:50:33AM +0200, Dmitry Vyukov wrote: > Stack unwinding produces large amounts of uninteresting coverage. > It's called from KASAN kmalloc/kfree hooks, fault injection, etc. > It's not particularly useful and is not a function of system call args. > Ignore that code. This stems from KCOV's purpose being guiding syzkaller as opposed to it being a more general coverage tool, right? Is that spelled out anywhere? Anyway, Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> > Signed-off-by: Dmitry Vyukov <dvyukov@google.com> > Reviewed-by: Alexander Potapenko <glider@google.com> > Reviewed-by: Marco Elver <elver@google.com> > Cc: x86@kernel.org > Cc: linux-kernel@vger.kernel.org > Cc: syzkaller@googlegroups.com > --- > arch/x86/kernel/Makefile | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile > index 20a0dd51700a..cd49ebfae984 100644 > --- a/arch/x86/kernel/Makefile > +++ b/arch/x86/kernel/Makefile > @@ -39,6 +39,14 @@ KMSAN_SANITIZE_sev.o := n > # first second. > KCOV_INSTRUMENT_head$(BITS).o := n > KCOV_INSTRUMENT_sev.o := n > +# These are called from save_stack_trace() on debug paths, > +# and produce large amounts of uninteresting coverage. > +KCOV_INSTRUMENT_stacktrace.o := n > +KCOV_INSTRUMENT_dumpstack.o := n > +KCOV_INSTRUMENT_dumpstack_$(BITS).o := n > +KCOV_INSTRUMENT_unwind_orc.o := n > +KCOV_INSTRUMENT_unwind_frame.o := n > +KCOV_INSTRUMENT_unwind_guess.o := n > > CFLAGS_irq.o := -I $(src)/../include/asm/trace > > -- > 2.45.2.505.gda0bf45e8d-goog >
On Wed, 19 Jun 2024 at 13:23, Peter Zijlstra <peterz@infradead.org> wrote: > > On Tue, Jun 11, 2024 at 09:50:33AM +0200, Dmitry Vyukov wrote: > > Stack unwinding produces large amounts of uninteresting coverage. > > It's called from KASAN kmalloc/kfree hooks, fault injection, etc. > > It's not particularly useful and is not a function of system call args. > > Ignore that code. > > This stems from KCOV's purpose being guiding syzkaller as opposed to it > being a more general coverage tool, right? > > Is that spelled out anywhere? It may be used for other similar purposes as well, e.g. collecting unit test coverage (not the whole kernel, but a single specific test provided that even other tests can run and collect their own coverage in parallel). It's spelled explicitly in the docs: https://elixir.bootlin.com/linux/latest/source/Documentation/dev-tools/kcov.rst """ KCOV collects and exposes kernel code coverage information in a form suitable for coverage-guided fuzzing .... Coverage collection is enabled on a task basis, and thus KCOV can capture precise coverage of a single system call. Note that KCOV does not aim to collect as much coverage as possible. It aims to collect more or less stable coverage that is a function of syscall inputs. To achieve this goal, it does not collect coverage in soft/hard interrupts... """ > Anyway, > > Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Thanks for your reviews, Peter! > > Signed-off-by: Dmitry Vyukov <dvyukov@google.com> > > Reviewed-by: Alexander Potapenko <glider@google.com> > > Reviewed-by: Marco Elver <elver@google.com> > > Cc: x86@kernel.org > > Cc: linux-kernel@vger.kernel.org > > Cc: syzkaller@googlegroups.com > > --- > > arch/x86/kernel/Makefile | 8 ++++++++ > > 1 file changed, 8 insertions(+) > > > > diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile > > index 20a0dd51700a..cd49ebfae984 100644 > > --- a/arch/x86/kernel/Makefile > > +++ b/arch/x86/kernel/Makefile > > @@ -39,6 +39,14 @@ KMSAN_SANITIZE_sev.o := n > > # first second. > > KCOV_INSTRUMENT_head$(BITS).o := n > > KCOV_INSTRUMENT_sev.o := n > > +# These are called from save_stack_trace() on debug paths, > > +# and produce large amounts of uninteresting coverage. > > +KCOV_INSTRUMENT_stacktrace.o := n > > +KCOV_INSTRUMENT_dumpstack.o := n > > +KCOV_INSTRUMENT_dumpstack_$(BITS).o := n > > +KCOV_INSTRUMENT_unwind_orc.o := n > > +KCOV_INSTRUMENT_unwind_frame.o := n > > +KCOV_INSTRUMENT_unwind_guess.o := n > > > > CFLAGS_irq.o := -I $(src)/../include/asm/trace > > > > -- > > 2.45.2.505.gda0bf45e8d-goog > > > > -- > You received this message because you are subscribed to the Google Groups "syzkaller" group. > To unsubscribe from this group and stop receiving emails from it, send an email to syzkaller+unsubscribe@googlegroups.com. > To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller/20240619112332.GL31592%40noisy.programming.kicks-ass.net.
On Tue, Jun 11, 2024 at 9:50 AM 'Dmitry Vyukov' via syzkaller <syzkaller@googlegroups.com> wrote: > > Stack unwinding produces large amounts of uninteresting coverage. > It's called from KASAN kmalloc/kfree hooks, fault injection, etc. > It's not particularly useful and is not a function of system call args. > Ignore that code. > > Signed-off-by: Dmitry Vyukov <dvyukov@google.com> > Reviewed-by: Alexander Potapenko <glider@google.com> > Reviewed-by: Marco Elver <elver@google.com> > Cc: x86@kernel.org > Cc: linux-kernel@vger.kernel.org > Cc: syzkaller@googlegroups.com > --- > arch/x86/kernel/Makefile | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile > index 20a0dd51700a..cd49ebfae984 100644 > --- a/arch/x86/kernel/Makefile > +++ b/arch/x86/kernel/Makefile > @@ -39,6 +39,14 @@ KMSAN_SANITIZE_sev.o := n > # first second. > KCOV_INSTRUMENT_head$(BITS).o := n > KCOV_INSTRUMENT_sev.o := n > +# These are called from save_stack_trace() on debug paths, > +# and produce large amounts of uninteresting coverage. > +KCOV_INSTRUMENT_stacktrace.o := n > +KCOV_INSTRUMENT_dumpstack.o := n > +KCOV_INSTRUMENT_dumpstack_$(BITS).o := n > +KCOV_INSTRUMENT_unwind_orc.o := n > +KCOV_INSTRUMENT_unwind_frame.o := n > +KCOV_INSTRUMENT_unwind_guess.o := n > > CFLAGS_irq.o := -I $(src)/../include/asm/trace > > -- Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
© 2016 - 2026 Red Hat, Inc.