linux-kernel - Re: [PATCH] [v2] ubsan, kcsan: don't combine sanitizer with kcov on clang

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Date:   Wed, 13 May 2020 13:02:18 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Marco Elver <elver@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH] [v2] ubsan, kcsan: don't combine sanitizer with kcov on
 clang

On Thu, May 07, 2020 at 06:25:31PM +0200, Arnd Bergmann wrote:
> Clang does not allow -fsanitize-coverage=trace-{pc,cmp} together
> with -fsanitize=bounds or with ubsan:
> 
> clang: error: argument unused during compilation: '-fsanitize-coverage=trace-pc' [-Werror,-Wunused-command-line-argument]
> clang: error: argument unused during compilation: '-fsanitize-coverage=trace-cmp' [-Werror,-Wunused-command-line-argument]
> 
> To avoid the warning, check whether clang can handle this correctly
> or disallow ubsan and kcsan when kcov is enabled.
> 
> Link: https://bugs.llvm.org/show_bug.cgi?id=45831
> Link: https://lore.kernel.org/lkml/20200505142341.1096942-1-arnd@arndb.de
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Applied for v5.9 and pushed, thank you!

							Thanx, Paul

> ---
> v2: this implements Marco's suggestion to check what the compiler
> actually supports, and references the bug report I now opened.
> 
> Let's wait for replies on that bug report before this gets applied,
> in case the feedback there changes the conclusion.
> ---
>  lib/Kconfig.kcsan | 11 +++++++++++
>  lib/Kconfig.ubsan | 11 +++++++++++
>  2 files changed, 22 insertions(+)
> 
> diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
> index ea28245c6c1d..a7276035ca0d 100644
> --- a/lib/Kconfig.kcsan
> +++ b/lib/Kconfig.kcsan
> @@ -3,9 +3,20 @@
>  config HAVE_ARCH_KCSAN
>  	bool
>  
> +config KCSAN_KCOV_BROKEN
> +	def_bool KCOV && CC_HAS_SANCOV_TRACE_PC
> +	depends on CC_IS_CLANG
> +	depends on !$(cc-option,-Werror=unused-command-line-argument -fsanitize=thread -fsanitize-coverage=trace-pc)
> +	help
> +	  Some versions of clang support either KCSAN and KCOV but not the
> +	  combination of the two.
> +	  See https://bugs.llvm.org/show_bug.cgi?id=45831 for the status
> +	  in newer releases.
> +
>  menuconfig KCSAN
>  	bool "KCSAN: dynamic data race detector"
>  	depends on HAVE_ARCH_KCSAN && DEBUG_KERNEL && !KASAN
> +	depends on !KCSAN_KCOV_BROKEN
>  	select STACKTRACE
>  	help
>  	  The Kernel Concurrency Sanitizer (KCSAN) is a dynamic
> diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
> index 929211039bac..a5ba2fd51823 100644
> --- a/lib/Kconfig.ubsan
> +++ b/lib/Kconfig.ubsan
> @@ -26,9 +26,20 @@ config UBSAN_TRAP
>  	  the system. For some system builders this is an acceptable
>  	  trade-off.
>  
> +config UBSAN_KCOV_BROKEN
> +	def_bool KCOV && CC_HAS_SANCOV_TRACE_PC
> +	depends on CC_IS_CLANG
> +	depends on !$(cc-option,-Werror=unused-command-line-argument -fsanitize=bounds -fsanitize-coverage=trace-pc)
> +	help
> +	  Some versions of clang support either UBSAN or KCOV but not the
> +	  combination of the two.
> +	  See https://bugs.llvm.org/show_bug.cgi?id=45831 for the status
> +	  in newer releases.
> +
>  config UBSAN_BOUNDS
>  	bool "Perform array index bounds checking"
>  	default UBSAN
> +	depends on !UBSAN_KCOV_BROKEN
>  	help
>  	  This option enables detection of directly indexed out of bounds
>  	  array accesses, where the array size is known at compile time.
> -- 
> 2.26.0
>