Re: [PATCH v4 27/31] kcov: test compiler capability in Kconfig and correct dependency

[Kees Cook]

On Wed, May 16, 2018 at 11:17 PM, Masahiro Yamada
<yamada.masahiro@xxxxxxxxxxxxx> wrote:
> 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@xxxxxxxxxxxxx>

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-Kees

-- 
Kees Cook
Pixel Security