linux-kernel - Re: [PATCH] x86/boot: clean up headers

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Date:   Fri, 1 Mar 2019 17:13:08 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     bp@...en8.de, niravd@...gle.com,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/boot: clean up headers

On Fri, Mar 01, 2019 at 04:07:14PM -0800, Nick Desaulniers wrote:
> The inclusion of <linux/kernel.h> was causing issue as the definition of
> __arch_hweight64 from arch/x86/include/asm/arch_hweight.h eventually gets
> included. The definition is problematic when compiled with -m16 (all code
> in arch/x86/boot/ is) as the "D" inline assembly constraint is rejected
> by both compilers when passed an argument of type long long (regardless
> of signedness, anything smaller is fine).
> 
> Because GCC performs inlining before semantic analysis, and
> __arch_hweight64 is dead in this translation unit, GCC does not report
> any issues at compile time.  Clang does the semantic analysis in the
> front end, before inlining (run in the middle) can determine the code is
> dead. I consider this another case of PR33587, which I think we can do
> more work to solve.
> 
> It turns out that arch/x86/boot/string.c doesn't actually need
> linux/kernel.h, simply linux/limits.h and linux/compiler.h. Include them,
> and sort the headers alphabetically.
> 
> Link: https://bugs.llvm.org/show_bug.cgi?id=33587
> Link: https://github.com/ClangBuiltLinux/linux/issues/347
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>

Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
Tested-by: Nathan Chancellor <natechancellor@...il.com>

> ---
> Note that this only regresses for us on linux-next (not mainline).
> 
>  arch/x86/boot/string.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/boot/string.c b/arch/x86/boot/string.c
> index 315a67b8896b..f149316116d0 100644
> --- a/arch/x86/boot/string.c
> +++ b/arch/x86/boot/string.c
> @@ -12,10 +12,11 @@
>   * Very basic string functions
>   */
>  
> -#include <linux/types.h>
> -#include <linux/kernel.h>
> -#include <linux/errno.h>
>  #include <asm/asm.h>
> +#include <linux/compiler.h>
> +#include <linux/errno.h>
> +#include <linux/limits.h>
> +#include <linux/types.h>
>  #include "ctype.h"
>  #include "string.h"
>  
> -- 
> 2.21.0.352.gf09ad66450-goog
>