linux-kernel - [PATCH v2 5/5] LoongArch: Enable jump table with GCC for objtool

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Message-ID: <20241105123906.26072-6-yangtiezhu@loongson.cn>
Date: Tue,  5 Nov 2024 20:39:06 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Cc: loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 5/5] LoongArch: Enable jump table with GCC for objtool

For now, it is time to remove the compiler option -fno-jump-tables
to enable jump table for objtool if the compiler is GCC and it has
the compiler option -mannotate-tablejump, otherwise still keep the
compiler option -fno-jump-tables to maintain compatibility with the
older compilers.

By the way, the compiler behaviors are different for various archs,
there are some corner issues after removing -fno-jump-tables if the
compiler is Clang, so just keep the compiler option -fno-jump-tables
for Clang at present.

Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
---
 arch/loongarch/Kconfig  | 3 +++
 arch/loongarch/Makefile | 9 +++++++++
 2 files changed, 12 insertions(+)

diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index bb35c34f86d2..500ee9b2cd88 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -284,6 +284,9 @@ config AS_HAS_LBT_EXTENSION
 config AS_HAS_LVZ_EXTENSION
 	def_bool $(as-instr,hvcl 0)
 
+config CC_HAS_ANNOTATE_TABLEJUMP
+	def_bool $(cc-option,-mannotate-tablejump)
+
 menu "Kernel type and options"
 
 source "kernel/Kconfig.hz"
diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
index ae3f80622f4c..61484df4eccc 100644
--- a/arch/loongarch/Makefile
+++ b/arch/loongarch/Makefile
@@ -101,8 +101,17 @@ KBUILD_AFLAGS			+= $(call cc-option,-mthin-add-sub) $(call cc-option,-Wa$(comma)
 KBUILD_CFLAGS			+= $(call cc-option,-mthin-add-sub) $(call cc-option,-Wa$(comma)-mthin-add-sub)
 
 ifdef CONFIG_OBJTOOL
+ifdef CONFIG_CC_IS_GCC
+ifdef CONFIG_CC_HAS_ANNOTATE_TABLEJUMP
+KBUILD_CFLAGS			+= $(call cc-option,-mannotate-tablejump)
+else
 KBUILD_CFLAGS			+= -fno-jump-tables
 endif
+endif
+ifdef CONFIG_CC_IS_CLANG
+KBUILD_CFLAGS			+= -fno-jump-tables
+endif
+endif
 
 KBUILD_RUSTFLAGS		+= --target=loongarch64-unknown-none-softfloat
 KBUILD_RUSTFLAGS_KERNEL		+= -Zdirect-access-external-data=yes
-- 
2.42.0