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Date:   Mon, 30 Nov 2020 20:51:46 -0700
From:   Nathan Chancellor <natechancellor@gmail.com>
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        David Woodhouse <dwmw2@infradead.org>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org,
        clang-built-linux@googlegroups.com
Subject: Re: [PATCH] x86, build: remove -m16 workaround for unsupported
 versions of GCC
Message-ID: <20201201035146.GA1469908@ubuntu-m3-large-x86>
References: <20201201011307.3676986-1-ndesaulniers@google.com>
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In-Reply-To: <20201201011307.3676986-1-ndesaulniers@google.com>
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On Mon, Nov 30, 2020 at 05:13:06PM -0800, 'Nick Desaulniers' via Clang Built Linux wrote:
> A revert of the following two commits.
> commit de3accdaec88 ("x86, build: Build 16-bit code with -m16 where
> possible")
> commit a9cfccee6604 ("x86, build: Change code16gcc.h from a C header to
> an assembly header")
> 
> Since commit 0bddd227f3dc ("Documentation: update for gcc 4.9
> requirement") the minimum supported version of GCC is gcc-4.9.  It's now
> safe to remove this code.
> 
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>

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

> ---
>  arch/x86/Makefile         |  9 +--------
>  arch/x86/boot/code16gcc.h | 12 ------------
>  2 files changed, 1 insertion(+), 20 deletions(-)
>  delete mode 100644 arch/x86/boot/code16gcc.h
> 
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index 1bf21746f4ce..7116da3980be 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -24,14 +24,7 @@ endif
>  
>  # How to compile the 16-bit code.  Note we always compile for -march=i386;
>  # that way we can complain to the user if the CPU is insufficient.
> -#
> -# The -m16 option is supported by GCC >= 4.9 and clang >= 3.5. For
> -# older versions of GCC, include an *assembly* header to make sure that
> -# gcc doesn't play any games behind our back.
> -CODE16GCC_CFLAGS := -m32 -Wa,$(srctree)/arch/x86/boot/code16gcc.h
> -M16_CFLAGS	 := $(call cc-option, -m16, $(CODE16GCC_CFLAGS))
> -
> -REALMODE_CFLAGS	:= $(M16_CFLAGS) -g -Os -DDISABLE_BRANCH_PROFILING \
> +REALMODE_CFLAGS	:= -m16 -g -Os -DDISABLE_BRANCH_PROFILING \
>  		   -Wall -Wstrict-prototypes -march=i386 -mregparm=3 \
>  		   -fno-strict-aliasing -fomit-frame-pointer -fno-pic \
>  		   -mno-mmx -mno-sse
> diff --git a/arch/x86/boot/code16gcc.h b/arch/x86/boot/code16gcc.h
> deleted file mode 100644
> index e19fd7536307..000000000000
> --- a/arch/x86/boot/code16gcc.h
> +++ /dev/null
> @@ -1,12 +0,0 @@
> -/* SPDX-License-Identifier: GPL-2.0 */
> -#
> -# code16gcc.h
> -#
> -# This file is added to the assembler via -Wa when compiling 16-bit C code.
> -# This is done this way instead via asm() to make sure gcc does not reorder
> -# things around us.
> -#
> -# gcc 4.9+ has a real -m16 option so we can drop this hack long term.
> -#
> -
> -	.code16gcc
> -- 
> 2.29.2.454.gaff20da3a2-goog
>