kcov: test compiler capability in Kconfig and correct dependency
As Documentation/kbuild/kconfig-language.txt notes, 'select' should be
be used with care - it forces a lower limit of another symbol, ignoring
the dependency. Currently, KCOV can select GCC_PLUGINS even if arch
does not select HAVE_GCC_PLUGINS. This could cause the unmet direct
dependency.
Now that Kconfig can test compiler capability, let's handle this in a
more sophisticated way.
There are two ways to enable KCOV; use the compiler that natively
supports -fsanitize-coverage=trace-pc, or build the SANCOV plugin if
the compiler has ability to build GCC plugins. Hence, the correct
dependency for KCOV is:
depends on CC_HAS_SANCOV_TRACE_PC || GCC_PLUGINS
You do not need to build the SANCOV plugin if the compiler already
supports -fsanitize-coverage=trace-pc. Hence, the select should be:
select GCC_PLUGIN_SANCOV if !CC_HAS_SANCOV_TRACE_PC
With this, GCC_PLUGIN_SANCOV is selected only when necessary, so
scripts/Makefile.gcc-plugins can be cleaner.
I also cleaned up Kconfig and scripts/Makefile.kcov as well.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index eb885942..d543c65 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -736,12 +736,15 @@
only for x86_64. KCOV requires testing on other archs, and most likely
disabling of instrumentation for some early boot code.
+config CC_HAS_SANCOV_TRACE_PC
+ def_bool $(cc-option,-fsanitize-coverage=trace-pc)
+
config KCOV
bool "Code coverage for fuzzing"
depends on ARCH_HAS_KCOV
+ depends on CC_HAS_SANCOV_TRACE_PC || GCC_PLUGINS
select DEBUG_FS
- select GCC_PLUGINS if !COMPILE_TEST
- select GCC_PLUGIN_SANCOV if !COMPILE_TEST
+ select GCC_PLUGIN_SANCOV if !CC_HAS_SANCOV_TRACE_PC
help
KCOV exposes kernel code coverage information in a form suitable
for coverage-guided fuzzing (randomized testing).
@@ -755,7 +758,7 @@
config KCOV_ENABLE_COMPARISONS
bool "Enable comparison operands collection by KCOV"
depends on KCOV
- default n
+ depends on $(cc-option,-fsanitize-coverage=trace-cmp)
help
KCOV also exposes operands of every comparison in the instrumented
code along with operand sizes and PCs of the comparison instructions.
@@ -765,7 +768,7 @@
config KCOV_INSTRUMENT_ALL
bool "Instrument all code by default"
depends on KCOV
- default y if KCOV
+ default y
help
If you are doing generic system call fuzzing (like e.g. syzkaller),
then you will want to instrument the whole kernel and you should
