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SubjectRe: [PATCH 07/43] compiler_attributes.h: add __disable_sanitizer_instrumentation
On Tue, Dec 14, 2021 at 05:20:14PM +0100, Alexander Potapenko wrote:
> The new attribute maps to
> __attribute__((disable_sanitizer_instrumentation)), which will be
> supported by Clang >= 14.0. Future support in GCC is also possible.
>
> This attribute disables compiler instrumentation for kernel sanitizer
> tools, making it easier to implement noinstr. It is different from the
> existing __no_sanitize* attributes, which may still allow certain types
> of instrumentation to prevent false positives.

When you say the __no_sanitize* attributes allow some instrumentation, does
that apply to any of the existing KASAN/KCSAN/KCOV support, or just for KMSAN?

The documentation just says the same as the commit message:

| This is not the same as __attribute__((no_sanitize(...))), which depending on
| the tool may still insert instrumentation to prevent false positive reports.

... which implies the other instrumentation might not be suprressed.

I ask because architectures which select ARCH_WANTS_NO_INSTR *need* to be able
to suppress all instrumentation. It's fine if that means they need a new
version of clang for KMSAN, but if there's latent instrumentation we have more
bugs to fix first...

Thanks,
Mark.

> Signed-off-by: Alexander Potapenko <glider@google.com>
> ---
> Link: https://linux-review.googlesource.com/id/Ic0123ce99b33ab7d5ed1ae90593425be8d3d774a
> ---
> include/linux/compiler_attributes.h | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
> index b9121afd87331..37e2600202216 100644
> --- a/include/linux/compiler_attributes.h
> +++ b/include/linux/compiler_attributes.h
> @@ -308,6 +308,24 @@
> # define __compiletime_warning(msg)
> #endif
>
> +/*
> + * Optional: only supported since clang >= 14.0
> + *
> + * clang: https://clang.llvm.org/docs/AttributeReference.html#disable-sanitizer-instrumentation
> + *
> + * disable_sanitizer_instrumentation is not always similar to
> + * no_sanitize((<sanitizer-name>)): the latter may still let specific sanitizers
> + * insert code into functions to prevent false positives. Unlike that,
> + * disable_sanitizer_instrumentation prevents all kinds of instrumentation to
> + * functions with the attribute.
> + */
> +#if __has_attribute(disable_sanitizer_instrumentation)
> +# define __disable_sanitizer_instrumentation \
> + __attribute__((disable_sanitizer_instrumentation))
> +#else
> +# define __disable_sanitizer_instrumentation
> +#endif
> +
> /*
> * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-weak-function-attribute
> * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-weak-variable-attribute
> --
> 2.34.1.173.g76aa8bc2d0-goog
>

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