linux-kernel - [PATCH v2 2/2] MIPS: Loongson{2ef,64}: Wrap -mno-branch-likely with cc-option

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Date:   Tue, 25 Jan 2022 15:19:25 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Huacai Chen <chenhuacai@...nel.org>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH v2 2/2] MIPS: Loongson{2ef,64}: Wrap -mno-branch-likely with cc-option

This flag is not supported by clang, which results in a warning:

  clang-14: warning: argument unused during compilation: '-mno-branch-likely' [-Wunused-command-line-argument]

This breaks cc-option, which adds -Werror to make this warning fatal and
catch flags that are not supported.

Wrap this flag in cc-option so that it does not cause cc-option to fail,
which can cause randconfigs to be really noisy, due to warnings not
getting disabled that should be.

Additionally, move the cc-option check to Kconfig so that the check is
done at configuration time, rather than build time, as builds with no
configuration change will be quicker because the cc-option call will not
need to happen in those instances.

Suggested-by: Nick Desaulniers <ndesaulniers@...gle.com>
Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---

v1 -> v2: https://lore.kernel.org/r/20220120214001.1879469-2-nathan@kernel.org/

* Move cc-option call to Kconfig (Nick).
* Also apply to loongson2ef, even though this will not currently build
  with clang.

 arch/mips/Kconfig              | 4 ++++
 arch/mips/loongson2ef/Platform | 3 ++-
 arch/mips/loongson64/Platform  | 3 ++-
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 058446f01487..da6b3e0501a7 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -3202,6 +3202,10 @@ config MIPS32_N32
 
 	  If unsure, say N.
 
+config CC_HAS_MNO_BRANCH_LIKELY
+	def_bool y
+	depends on $(cc-option,-mno-branch-likely)
+
 menu "Power management options"
 
 config ARCH_HIBERNATION_POSSIBLE
diff --git a/arch/mips/loongson2ef/Platform b/arch/mips/loongson2ef/Platform
index 50e659aca543..eebabf9df6ac 100644
--- a/arch/mips/loongson2ef/Platform
+++ b/arch/mips/loongson2ef/Platform
@@ -41,6 +41,7 @@ cflags-y += $(call cc-option,-mno-loongson-mmi)
 # Loongson Machines' Support
 #
 
-cflags-$(CONFIG_MACH_LOONGSON2EF) += -I$(srctree)/arch/mips/include/asm/mach-loongson2ef -mno-branch-likely
+cflags-$(CONFIG_MACH_LOONGSON2EF) += -I$(srctree)/arch/mips/include/asm/mach-loongson2ef
+cflags-$(CONFIG_CC_HAS_MNO_BRANCH_LIKELY) += -mno-branch-likely
 load-$(CONFIG_LEMOTE_FULOONG2E) += 0xffffffff80100000
 load-$(CONFIG_LEMOTE_MACH2F) += 0xffffffff80200000
diff --git a/arch/mips/loongson64/Platform b/arch/mips/loongson64/Platform
index f2a08a185ee2..473404cae1c4 100644
--- a/arch/mips/loongson64/Platform
+++ b/arch/mips/loongson64/Platform
@@ -18,5 +18,6 @@ cflags-y += $(call cc-option,-mno-loongson-mmi)
 # Loongson Machines' Support
 #
 
-cflags-$(CONFIG_MACH_LOONGSON64) += -I$(srctree)/arch/mips/include/asm/mach-loongson64 -mno-branch-likely
+cflags-$(CONFIG_MACH_LOONGSON64) += -I$(srctree)/arch/mips/include/asm/mach-loongson64
+cflags-$(CONFIG_CC_HAS_MNO_BRANCH_LIKELY) += -mno-branch-likely
 load-$(CONFIG_CPU_LOONGSON64) += 0xffffffff80200000
-- 
2.35.0