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SubjectRe: [PATCH v2 16/21] kcov: imply GCC_PLUGINS and GCC_PLUGIN_SANCOV instead of select'ing them
On Mon, Mar 26, 2018 at 10:29 PM, Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
> As Documentation/kbuild/kconfig-language.txt notes, 'select' should be
> used with care - it forces a lower limit of another symbol, ignoring
> the dependency. In this case, KCOV can select GCC_PLUGINS even if
> 'depends on HAVE_GCC_PLUGINS' is unmet.
>
> 'imply' is modest enough to observe the dependency, and this makes
> sense. If you enable KCOV, you will probably want to enable
> GCC_PLUGIN_SANCOV, but it should not break the dependency.
>
> I also remove unneeded code, I just happened to notice.
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> - Drop depends on GCC_VERSION
>
> ---
>
> Changes in v2: None
>
> lib/Kconfig.debug | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 5be22e4..8243c9d 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -743,8 +743,8 @@ config KCOV
> bool "Code coverage for fuzzing"
> depends on ARCH_HAS_KCOV
> select DEBUG_FS
> - select GCC_PLUGINS if !COMPILE_TEST
> - select GCC_PLUGIN_SANCOV if !COMPILE_TEST
> + imply GCC_PLUGINS
> + imply GCC_PLUGIN_SANCOV
> help
> KCOV exposes kernel code coverage information in a form suitable
> for coverage-guided fuzzing (randomized testing).

Actually, I think this can be improved, as KCOV should depend on either:

-fsanitize-coverage=trace-pc support (in gcc 6+, see scripts/Makefile.kcov)

or

GCC_PLUGIN_SANCOV (which provides the trace-pc support via the plugin
for gcc before 6)

> @@ -758,7 +758,6 @@ config KCOV
> 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.

Similarly, this depends on -fsanitize-coverage=trace-cmp

> @@ -768,7 +767,7 @@ 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
> --
> 2.7.4
>

-Kees

--
Kees Cook
Pixel Security

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