linux-kernel - Re: [PATCH v3 5/7] selftests/x86: avoid -no-pie warnings from clang during compilation

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Date: Fri, 7 Jun 2024 15:23:11 -0700
From: John Hubbard <jhubbard@...dia.com>
To: Shuah Khan <shuah@...nel.org>
CC: angquan yu <angquan21@...il.com>, "Kirill A . Shutemov"
	<kirill.shutemov@...ux.intel.com>, Ingo Molnar <mingo@...nel.org>, Binbin Wu
	<binbin.wu@...ux.intel.com>, Alexey Dobriyan <adobriyan@...il.com>, "Rick
 Edgecombe" <rick.p.edgecombe@...el.com>, Sohil Mehta <sohil.mehta@...el.com>,
	Yu-cheng Yu <yu-cheng.yu@...el.com>, Dave Hansen
	<dave.hansen@...ux.intel.com>, Muhammad Usama Anjum
	<usama.anjum@...labora.com>, Valentin Obst <kernel@...entinobst.de>,
	<linux-kselftest@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
	<llvm@...ts.linux.dev>, <x86@...nel.org>
Subject: Re: [PATCH v3 5/7] selftests/x86: avoid -no-pie warnings from clang
 during compilation

On 5/31/24 12:38 PM, John Hubbard wrote:
...
> diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile
> index d0bb32bd5538..5c8757a25998 100644
> --- a/tools/testing/selftests/x86/Makefile
> +++ b/tools/testing/selftests/x86/Makefile
> @@ -40,6 +40,13 @@ CFLAGS := -O2 -g -std=gnu99 -pthread -Wall $(KHDR_INCLUDES)
>   # call32_from_64 in thunks.S uses absolute addresses.
>   ifeq ($(CAN_BUILD_WITH_NOPIE),1)
>   CFLAGS += -no-pie
> +
> +ifneq ($(LLVM),)
> +# clang only wants to see -no-pie during linking. Here, we don't have a separate
> +# linking stage, so a compiler warning is unavoidable without (wastefully)
> +# restructuring the Makefile. Avoid this by simply disabling that warning.
> +CFLAGS += -Wno-unused-command-line-argument
> +endif
>   endif
>   
>   define gen-target-rule-32

This actually can be improved slightly, as per our latest tentative
decision about how to handle both LLVM=1 and CC=clang cases [1].

If this series goes via Shuah's next tree, then I can put the
CC_IS_CLANG fix from [1] on top of previous patches, that will work
nicely.

In other words, I think we can use this series as-is, and let the
CC_IS_CLANG fix proceed just after that. Because it gets better a piece
at a time: first we get rid of the warning for most cases, then we get
rid of it for the odd "make CC=clang" case as well.

[1] https://lore.kernel.org/6b32399f-d9c6-4df5-b1e5-755ef4acf25d@nvidia.com

thanks,
-- 
John Hubbard
NVIDIA