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From: Marco Elver <elver@google.com>
Date: Fri, 2 Feb 2024 10:57:11 +0100
Message-ID: <CANpmjNMCBvdM7Ni+vWCQwtJbbVskOdjSA+gjhgh6R3dKRqjXnA@mail.gmail.com>
Subject: Re: [PATCH] ubsan: Silence W=1 warnings in self-test
To: Kees Cook <keescook@chromium.org>
Cc: kernel test robot <lkp@intel.com>, linux-kernel@vger.kernel.org, 
	linux-hardening@vger.kernel.org
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On Fri, 2 Feb 2024 at 10:46, Kees Cook <keescook@chromium.org> wrote:
>
> Silence a handful of W=1 warnings in the UBSan selftest, which set
> variables without using them. For example:
>
>    lib/test_ubsan.c:101:6: warning: variable 'val1' set but not used [-Wunused-but-set-variable]
>      101 |         int val1 = 10;
>          |             ^

This is the shift_out_of_bounds test? It looks like the neg and wrap
variables are volatile but the written-to variables aren't.
Technically the compiler just has to emit the reads to neg and wrap,
and can entirely omit the writes to val1 and val2.

Does making it volatile fix the warning?

>
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202401310423.XpCIk6KO-lkp@intel.com/
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  lib/Makefile | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/lib/Makefile b/lib/Makefile
> index 6b09731d8e61..bc36a5c167db 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -69,6 +69,7 @@ obj-$(CONFIG_HASH_KUNIT_TEST) += test_hash.o
>  obj-$(CONFIG_TEST_IDA) += test_ida.o
>  obj-$(CONFIG_TEST_UBSAN) += test_ubsan.o
>  CFLAGS_test_ubsan.o += $(call cc-disable-warning, vla)
> +CFLAGS_test_ubsan.o += $(call cc-disable-warning, unused-but-set-variable)
>  UBSAN_SANITIZE_test_ubsan.o := y
>  obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
>  obj-$(CONFIG_TEST_LIST_SORT) += test_list_sort.o
> --
> 2.34.1
>