linux-kernel - [PATCH] x86, build: remove -m16 workaround for unsupported versions of GCC

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Message-Id: <20201201011307.3676986-1-ndesaulniers@google.com>
Date:   Mon, 30 Nov 2020 17:13:06 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: [PATCH] x86, build: remove -m16 workaround for unsupported versions
 of GCC

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@...gle.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