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Date: Sun, 10 Jun 2018 23:19:47 +0900
From: Masahiro Yamada <yamada.masahiro@...ionext.com>
To: Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Kees Cook <keescook@...omium.org>,
Nicholas Piggin <npiggin@...il.com>,
"Luis R . Rodriguez" <mcgrof@...e.com>,
Randy Dunlap <rdunlap@...radead.org>,
Ulf Magnusson <ulfalizer@...il.com>,
Sam Ravnborg <sam@...nborg.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Masahiro Yamada <yamada.masahiro@...ionext.com>
Subject: Re: [PATCH v5 27/31] kcov: test compiler capability in Kconfig and
correct dependency
2018-05-28 18:22 GMT+09:00 Masahiro Yamada <yamada.masahiro@...ionext.com>:
> 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@...ionext.com>
> Reviewed-by: Kees Cook <keescook@...omium.org>
> ---
>
> Changes in v5: None
> Changes in v4: None
> Changes in v3:
> - Replace the previous 'select -> imply' patch with
> a new approach
>
> Changes in v2:
> - Drop depends on GCC_VERSION
>
> Makefile | 2 +-
> lib/Kconfig.debug | 11 +++++++----
> scripts/Makefile.gcc-plugins | 6 +-----
> scripts/Makefile.kcov | 10 ++++++----
> 4 files changed, 15 insertions(+), 14 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index 80e0800..4b5a17a 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -626,7 +626,7 @@ all: vmlinux
> CFLAGS_GCOV := -fprofile-arcs -ftest-coverage \
> $(call cc-option,-fno-tree-loop-im) \
> $(call cc-disable-warning,maybe-uninitialized,)
> -export CFLAGS_GCOV CFLAGS_KCOV
> +export CFLAGS_GCOV
>
> # The arch Makefile can set ARCH_{CPP,A,C}FLAGS to override the default
> # values of the respective KBUILD_* variables
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index c40c7b7..b76cab2 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -736,12 +736,15 @@ config ARCH_HAS_KCOV
> 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
> config KCOV_ENABLE_COMPARISONS
> bool "Enable comparison operands collection by KCOV"
> depends on KCOV
> - default n
> + depends on $(cc-option,-fsanitize-coverage=trace-cmp)
> help
> KCOV also exposes operands of every comparison in the instrumented
> code along with operand sizes and PCs of the comparison instructions.
> @@ -765,7 +768,7 @@ config KCOV_ENABLE_COMPARISONS
> config KCOV_INSTRUMENT_ALL
> bool "Instrument all code by default"
> depends on KCOV
> - default y if KCOV
> + default y
> help
> If you are doing generic system call fuzzing (like e.g. syzkaller),
> then you will want to instrument the whole kernel and you should
> diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins
> index 7f5c862..0ce3802 100644
> --- a/scripts/Makefile.gcc-plugins
> +++ b/scripts/Makefile.gcc-plugins
> @@ -14,16 +14,12 @@ ifdef CONFIG_GCC_PLUGINS
> endif
>
> ifdef CONFIG_GCC_PLUGIN_SANCOV
> - ifeq ($(strip $(CFLAGS_KCOV)),)
> # It is needed because of the gcc-plugin.sh and gcc version checks.
> gcc-plugin-$(CONFIG_GCC_PLUGIN_SANCOV) += sancov_plugin.so
>
> - ifneq ($(PLUGINCC),)
> - CFLAGS_KCOV := $(SANCOV_PLUGIN)
> - else
> + ifeq ($(PLUGINCC),)
> $(warning warning: cannot use CONFIG_KCOV: -fsanitize-coverage=trace-pc is not supported by compiler)
> endif
> - endif
> endif
>
> gcc-plugin-$(CONFIG_GCC_PLUGIN_STRUCTLEAK) += structleak_plugin.so
> diff --git a/scripts/Makefile.kcov b/scripts/Makefile.kcov
> index 5cc7203..d71ba73 100644
> --- a/scripts/Makefile.kcov
> +++ b/scripts/Makefile.kcov
> @@ -1,7 +1,9 @@
> ifdef CONFIG_KCOV
> -CFLAGS_KCOV := $(call cc-option,-fsanitize-coverage=trace-pc,)
> -ifeq ($(CONFIG_KCOV_ENABLE_COMPARISONS),y)
> -CFLAGS_KCOV += $(call cc-option,-fsanitize-coverage=trace-cmp,)
> -endif
> +
> +kcov-flags-$(CONFIG_CC_HAS_SANCOV_TRACE_PC) += -fsanitize-coverage=trace-pc
> +kcov-flags-$(CONFIG_KCOV_ENABLE_COMPARISONS) += -fsanitize-coverage=trace-cmp
> +kcov-flags-$(CONFIG_GCC_PLUGIN_SANKOV) += -fplugin=$(objtree)/scripts/gcc-plugins/sancov_plugin.so
> +
This is my mistake.
SANKOV -> SANCOV
I fixed it locally.
> +export CFLAGS_KCOV := $(kcov-flags-y)
>
> endif
> --
> 2.7.4
>
> --
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--
Best Regards
Masahiro Yamada
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