[PATCH 2/3] Makefile: support flag -fsanitizer-coverage=trace-cmp

[Dmitry Vyukov]

From: Victor Chibotaru <tchibo@xxxxxxxxxx>

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@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Alexander Popov <alex.popov@xxxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Cc: Quentin Casasnovas <quentin.casasnovas@xxxxxxxxxx>
Cc: syzkaller@xxxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
Clang instrumentation:
https://clang.llvm.org/docs/SanitizerCoverage.html#tracing-data-flow
---
 Makefile              | 5 +++--
 lib/Kconfig.debug     | 8 ++++++++
 scripts/Makefile.kcov | 6 ++++++
 scripts/Makefile.lib  | 6 ++++++
 4 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index f9703f3223eb..bb117c42a785 100644
--- a/Makefile
+++ b/Makefile
@@ -374,7 +374,7 @@ 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,)
-
+CFLAGS_KCOV_COMPS := $(call cc-option,-fsanitize-coverage=trace-cmp,)
 
 # Use USERINCLUDE when you must reference the UAPI directories only.
 USERINCLUDE    := \
@@ -420,7 +420,7 @@ export MAKE AWK GENKSYMS INSTALLKERNEL PERL PYTHON UTS_MACHINE
 export HOSTCXX HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS
 
 export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS LDFLAGS
-export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE CFLAGS_GCOV CFLAGS_KCOV CFLAGS_KASAN CFLAGS_UBSAN
+export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE CFLAGS_GCOV CFLAGS_KCOV CFLAGS_KCOV_COMPS CFLAGS_KASAN CFLAGS_UBSAN
 export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE
 export KBUILD_AFLAGS_MODULE KBUILD_CFLAGS_MODULE KBUILD_LDFLAGS_MODULE
 export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL
@@ -822,6 +822,7 @@ KBUILD_CFLAGS   += $(call cc-option,-Werror=designated-init)
 KBUILD_ARFLAGS := $(call ar-option,D)
 
 include scripts/Makefile.kasan
+include scripts/Makefile.kcov
 include scripts/Makefile.extrawarn
 include scripts/Makefile.ubsan
 
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index d7e3f0bfe91e..85fc0db2e8af 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -777,6 +777,14 @@ 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 instrumented code.
+	  Note: currently only available if compiled with Clang.
+
 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..5d6e644cefed
--- /dev/null
+++ b/scripts/Makefile.kcov
@@ -0,0 +1,6 @@
+ifeq ($(CONFIG_KCOV_ENABLE_COMPARISONS),y)
+ifneq ($(cc-name),clang)
+  $(warning Cannot use CONFIG_KCOV_ENABLE_COMPARISONS: \
+            -fsanitize=trace-cmp is not supported by compiler)
+endif
+endif
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 58c05e5d9870..bb38cd33e15c 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 '/').
 
-- 
2.14.1.581.gf28d330327-goog