linux-kernel - [PATCH v2 1/2] x86/build: Do not add -falign flags unconditionally for clang

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Message-Id: <20210916184017.1881473-2-nathan@kernel.org>
Date:   Thu, 16 Sep 2021 11:40:16 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
        llvm@...ts.linux.dev, Nathan Chancellor <nathan@...nel.org>,
        kernel test robot <lkp@...el.com>,
        Borislav Petkov <bp@...e.de>
Subject: [PATCH v2 1/2] x86/build: Do not add -falign flags unconditionally for clang

clang does not support -falign-jumps and only recently gained support
for -falign-loops. When one of the configuration options that adds these
flags is enabled, clang warns and all cc-{disable-warning,option} that
follow fail because -Werror gets added to test for the presence of this
warning:

clang-14: warning: optimization flag '-falign-jumps=0' is not supported
[-Wignored-optimization-argument]

To resolve this, add a couple of cc-option calls when building with
clang; gcc has supported these options since 3.2 so there is no point in
testing for their support. -falign-functions was implemented in clang-7,
-falign-loops was implemented in clang-14, and -falign-jumps has not
been implemented yet.

Link: https://lore.kernel.org/r/YSQE2f5teuvKLkON@Ryzen-9-3900X.localdomain/
Link: https://lore.kernel.org/r/20210824022640.2170859-2-nathan@kernel.org/
Reported-by: kernel test robot <lkp@...el.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
Acked-by: Borislav Petkov <bp@...e.de>
Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---
 arch/x86/Makefile_32.cpu | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/x86/Makefile_32.cpu b/arch/x86/Makefile_32.cpu
index e7355f8b51c2..94834c4b5e5e 100644
--- a/arch/x86/Makefile_32.cpu
+++ b/arch/x86/Makefile_32.cpu
@@ -4,6 +4,12 @@
 
 tune		= $(call cc-option,-mtune=$(1),$(2))
 
+ifdef CONFIG_CC_IS_CLANG
+align		:= -falign-functions=0 $(call cc-option,-falign-jumps=0) $(call cc-option,-falign-loops=0)
+else
+align		:= -falign-functions=0 -falign-jumps=0 -falign-loops=0
+endif
+
 cflags-$(CONFIG_M486SX)		+= -march=i486
 cflags-$(CONFIG_M486)		+= -march=i486
 cflags-$(CONFIG_M586)		+= -march=i586
@@ -19,11 +25,11 @@ cflags-$(CONFIG_MK6)		+= -march=k6
 # They make zero difference whatsosever to performance at this time.
 cflags-$(CONFIG_MK7)		+= -march=athlon
 cflags-$(CONFIG_MK8)		+= $(call cc-option,-march=k8,-march=athlon)
-cflags-$(CONFIG_MCRUSOE)	+= -march=i686 -falign-functions=0 -falign-jumps=0 -falign-loops=0
-cflags-$(CONFIG_MEFFICEON)	+= -march=i686 $(call tune,pentium3) -falign-functions=0 -falign-jumps=0 -falign-loops=0
+cflags-$(CONFIG_MCRUSOE)	+= -march=i686 $(align)
+cflags-$(CONFIG_MEFFICEON)	+= -march=i686 $(call tune,pentium3) $(align)
 cflags-$(CONFIG_MWINCHIPC6)	+= $(call cc-option,-march=winchip-c6,-march=i586)
 cflags-$(CONFIG_MWINCHIP3D)	+= $(call cc-option,-march=winchip2,-march=i586)
-cflags-$(CONFIG_MCYRIXIII)	+= $(call cc-option,-march=c3,-march=i486) -falign-functions=0 -falign-jumps=0 -falign-loops=0
+cflags-$(CONFIG_MCYRIXIII)	+= $(call cc-option,-march=c3,-march=i486) $(align)
 cflags-$(CONFIG_MVIAC3_2)	+= $(call cc-option,-march=c3-2,-march=i686)
 cflags-$(CONFIG_MVIAC7)		+= -march=i686
 cflags-$(CONFIG_MCORE2)		+= -march=i686 $(call tune,core2)

base-commit: a9086b878b7fd65894eb8cb1fa395dd469970566
-- 
2.33.0