linux-kernel - Re: [PATCH v2 2/2] selftests/fchmodat2: fix clang build failure due to -static-libasan

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Date: Mon, 3 Jun 2024 15:39:36 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: John Hubbard <jhubbard@...dia.com>
Cc: Shuah Khan <shuah@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>,
	Ryan Roberts <ryan.roberts@....com>,
	Christian Brauner <brauner@...nel.org>,
	Muhammad Usama Anjum <usama.anjum@...labora.com>,
	Alexey Gladkov <legion@...nel.org>,
	Valentin Obst <kernel@...entinobst.de>,
	linux-kselftest@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>, llvm@...ts.linux.dev
Subject: Re: [PATCH v2 2/2] selftests/fchmodat2: fix clang build failure due
 to -static-libasan

On Fri, May 31, 2024 at 06:45:34PM -0700, John Hubbard wrote:
> gcc requires -static-libasan in order to ensure that Address Sanitizer's
> library is the first one loaded. However, this leads to build failures
> on clang, when building via:
> 
>     make LLVM=1 -C tools/testing/selftests
> 
> However, clang already does the right thing by default: it statically
> links the Address Sanitizer if -fsanitize is specified. Therefore,
> simply omit -static-libasan for clang builds. And leave behind a
> comment, because the whole reason for static linking might not be
> obvious.
> 
> Cc: Ryan Roberts <ryan.roberts@....com>
> Signed-off-by: John Hubbard <jhubbard@...dia.com>

Assuming that $(LLVM) is the correct conditional to test for:

Reviewed-by: Nathan Chancellor <nathan@...nel.org>

> ---
>  tools/testing/selftests/fchmodat2/Makefile | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/fchmodat2/Makefile b/tools/testing/selftests/fchmodat2/Makefile
> index 71ec34bf1501..4373cea79b79 100644
> --- a/tools/testing/selftests/fchmodat2/Makefile
> +++ b/tools/testing/selftests/fchmodat2/Makefile
> @@ -1,6 +1,15 @@
>  # SPDX-License-Identifier: GPL-2.0-or-later
>  
> -CFLAGS += -Wall -O2 -g -fsanitize=address -fsanitize=undefined -static-libasan $(KHDR_INCLUDES)
> +CFLAGS += -Wall -O2 -g -fsanitize=address -fsanitize=undefined $(KHDR_INCLUDES)
> +
> +# gcc requires -static-libasan in order to ensure that Address Sanitizer's
> +# library is the first one loaded. However, clang already statically links the
> +# Address Sanitizer if -fsanitize is specified. Therefore, simply omit
> +# -static-libasan for clang builds.
> +ifeq ($(LLVM),)
> +    CFLAGS += -static-libasan
> +endif
> +
>  TEST_GEN_PROGS := fchmodat2_test
>  
>  include ../lib.mk
> -- 
> 2.45.1
> 
>