linux-kernel - Re: [PATCH v2] selftests/vDSO: fix clang build errors and warnings

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Date: Tue, 11 Jun 2024 18:30:00 +0000
From: Carlos Llamas <cmllamas@...gle.com>
To: John Hubbard <jhubbard@...dia.com>
Cc: Shuah Khan <shuah@...nel.org>, Mark Brown <broonie@...nel.org>,
	Vincenzo Frascino <vincenzo.frascino@....com>,
	Colin Ian King <colin.i.king@...il.com>,
	Valentin Obst <kernel@...entinobst.de>,
	linux-kselftest@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>, llvm@...ts.linux.dev
Subject: Re: [PATCH v2] selftests/vDSO: fix clang build errors and warnings

On Mon, May 27, 2024 at 02:16:22PM -0700, John Hubbard wrote:
> When building with clang, via:
> 
>     make LLVM=1 -C tools/testing/selftests
> 
> ...there are several warnings, and an error. This fixes all of those and
> allows these tests to run and pass.

It might be best to split the 4 _different_ fixes into separate patches.

> 
> 1. Fix linker error (undefined reference to memcpy) by providing a local
>    version of memcpy.
> 
> 2. clang complains about using this form:
> 
>     if (g = h & 0xf0000000)
> 
> ...so factor out the assignment into a separate step.

There has been multiple attempts to fix this. I can see these two:
https://lore.kernel.org/all/20211206102931.1433871-1-anders.roxell@linaro.org/
https://lore.kernel.org/all/20240501002150.1370861-1-edliaw@google.com/

... I guess we somehow missed those?

> 
> 3. The code is passing a signed const char* to elf_hash(), which expects
>    a const unsigned char *. There are several callers, so fix this at
>    the source by allowing the function to accept a signed argument, and
>    then converting to unsigned operations, once inside the function.
> 

There is also a v4 fix for this item that was sent out here:
https://lore.kernel.org/all/20240506181951.1804451-1-edliaw@google.com/

> 4. clang doesn't have __attribute__((externally_visible)) and generates
>    a warning to that effect. Fortunately, gcc 12 and gcc 13 do not seem
>    to require that attribute in order to build, run and pass tests here,
>    so remove it.
> 
> [1] https://lore.kernel.org/all/20240329-selftests-libmk-llvm-rfc-v1-1-2f9ed7d1c49f@valentinobst.de/

What is this about? Left over from v1 maybe?

> 
> Signed-off-by: John Hubbard <jhubbard@...dia.com>
> ---

I would prefer to pick up the fixes from folks who sent out the patches
first but I'm fine either way.

Reviewed-by: Carlos Llamas <cmllamas@...gle.com>