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Subject[PATCH v3 2/3] Makefile: support flag -fsanitizer-coverage=trace-cmp
Date
From: Victor Chibotaru <tchibo@google.com>

The flag enables Clang instrumentation of comparison operations
(currently not supported by GCC). This instrumentation is needed by the
new KCOV device to collect comparison operands.

Signed-off-by: Victor Chibotaru <tchibo@google.com>
Signed-off-by: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Alexander Popov <alex.popov@linux.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Vegard Nossum <vegard.nossum@oracle.com>
Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Cc: syzkaller@googlegroups.com
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
---
Clang instrumentation:
https://clang.llvm.org/docs/SanitizerCoverage.html#tracing-data-flow

v3: - Andrey Ryabinin's comments: reinstated scripts/Makefile.kcov
and moved CFLAGS_KCOV there, dropped CFLAGS_KCOV_COMPS
- allow building with GCC
v2: - updated KCOV_ENABLE_COMPARISONS description
---
Makefile | 3 +--
lib/Kconfig.debug | 10 ++++++++++
scripts/Makefile.kcov | 7 +++++++
scripts/Makefile.lib | 6 ++++++
4 files changed, 24 insertions(+), 2 deletions(-)
create mode 100644 scripts/Makefile.kcov

diff --git a/Makefile b/Makefile
index 2835863bdd5a..43f642167d68 100644
--- a/Makefile
+++ b/Makefile
@@ -373,8 +373,6 @@ CFLAGS_KERNEL =
AFLAGS_KERNEL =
LDFLAGS_vmlinux =
CFLAGS_GCOV := -fprofile-arcs -ftest-coverage -fno-tree-loop-im $(call cc-disable-warning,maybe-uninitialized,)
-CFLAGS_KCOV := $(call cc-option,-fsanitize-coverage=trace-pc,)
-

# Use USERINCLUDE when you must reference the UAPI directories only.
USERINCLUDE := \
@@ -657,6 +655,7 @@ ifeq ($(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-goto.sh $(CC) $(KBUILD_CFLA
KBUILD_AFLAGS += -DCC_HAVE_ASM_GOTO
endif

+include scripts/Makefile.kcov
include scripts/Makefile.gcc-plugins

ifdef CONFIG_READABLE_ASM
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 2689b7c50c52..a10eb4e34719 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -759,6 +759,16 @@ config KCOV

For more details, see Documentation/dev-tools/kcov.rst.

+config KCOV_ENABLE_COMPARISONS
+ bool "Enable comparison operands collection by KCOV"
+ depends on KCOV
+ default n
+ help
+ KCOV also exposes operands of every comparison in the instrumented
+ code along with operand sizes and PCs of the comparison instructions.
+ These operands can be used by fuzzing engines to improve the quality
+ of fuzzing coverage.
+
config KCOV_INSTRUMENT_ALL
bool "Instrument all code by default"
depends on KCOV
diff --git a/scripts/Makefile.kcov b/scripts/Makefile.kcov
new file mode 100644
index 000000000000..5cc72037e423
--- /dev/null
+++ b/scripts/Makefile.kcov
@@ -0,0 +1,7 @@
+ifdef CONFIG_KCOV
+CFLAGS_KCOV := $(call cc-option,-fsanitize-coverage=trace-pc,)
+ifeq ($(CONFIG_KCOV_ENABLE_COMPARISONS),y)
+CFLAGS_KCOV += $(call cc-option,-fsanitize-coverage=trace-cmp,)
+endif
+
+endif
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 5e975fee0f5b..7ddd5932c832 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -142,6 +142,12 @@ _c_flags += $(if $(patsubst n%,, \
$(CFLAGS_KCOV))
endif

+ifeq ($(CONFIG_KCOV_ENABLE_COMPARISONS),y)
+_c_flags += $(if $(patsubst n%,, \
+ $(KCOV_INSTRUMENT_$(basetarget).o)$(KCOV_INSTRUMENT)$(CONFIG_KCOV_INSTRUMENT_ALL)), \
+ $(CFLAGS_KCOV_COMPS))
+endif
+
# If building the kernel in a separate objtree expand all occurrences
# of -Idir to -I$(srctree)/dir except for absolute paths (starting with '/').

--
2.14.2.920.gcf0c67979c-goog
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