linux-kernel - [PATCH] loongarch: Only select HAVE_OBJTOOL and allow ORC unwinder if the inline assembler supports R_LARCH_{32,64}

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Date: Tue,  4 Jun 2024 23:07:41 +0800
From: Xi Ruoyao <xry111@...111.site>
To: Huacai Chen <chenhuacai@...nel.org>,
	WANG Xuerui <kernel@...0n.name>,
	Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc: Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Youling Tang <tangyouling@...inos.cn>,
	Jinyang He <hejinyang@...ngson.cn>,
	loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev,
	mengqinggang@...ngson.cn,
	cailulu@...ngson.cn,
	wanglei@...ngson.cn,
	luweining@...ngson.cn,
	Yujie Liu <yujie.liu@...el.com>,
	Heng Qi <hengqi@...ux.alibaba.com>,
	Tejun Heo <tj@...nel.org>,
	Xi Ruoyao <xry111@...111.site>
Subject: [PATCH] loongarch: Only select HAVE_OBJTOOL and allow ORC unwinder if the inline assembler supports R_LARCH_{32,64}_PCREL

GAS <= 2.41 does not support generating R_LARCH_{32,64}_PCREL for
"label - ." and it generates R_LARCH_{ADD,SUB}{32,64} pairs instead.
objtool cannot handle R_LARCH_{ADD,SUB}{32,64} pair in __jump_table
(static key implementation) and etc. so it will produce some warnings.
This is causing the kernel CI systems to complain everywhere.

For GAS we can check if -mthin-add-sub option is available to know if
R_LARCH_{32,64}_PCREL are supported.

For Clang, we require Clang >= 18 and Clang >= 17 already supports
R_LARCH_{32,64}_PCREL, so we can always assume Clang is fine for
objtool.

Note that __jump_table is not generated by the compiler so
-fno-jump-table is completely irrelevant for this issue.

Fixes: cb8a2ef0848c ("LoongArch: Add ORC stack unwinder support")
Closes: https://lore.kernel.org/loongarch/Zl5m1ZlVmGKitAof@yujie-X299/
Closes: https://lore.kernel.org/loongarch/ZlY1gDDPi_mNrwJ1@slm.duckdns.org/
Closes: https://lore.kernel.org/loongarch/1717478006.038663-1-hengqi@linux.alibaba.com/
Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commitdiff;h=816029e06768
Link: https://github.com/llvm/llvm-project/commit/42cb3c6346fc
Signed-off-by: Xi Ruoyao <xry111@...111.site>
---
 arch/loongarch/Kconfig       | 5 ++++-
 arch/loongarch/Kconfig.debug | 1 +
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index e38139c576ee..e461a6c59f15 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -143,7 +143,7 @@ config LOONGARCH
 	select HAVE_LIVEPATCH
 	select HAVE_MOD_ARCH_SPECIFIC
 	select HAVE_NMI
-	select HAVE_OBJTOOL if AS_HAS_EXPLICIT_RELOCS
+	select HAVE_OBJTOOL if AS_HAS_EXPLICIT_RELOCS && AS_HAS_THIN_ADD_SUB
 	select HAVE_PCI
 	select HAVE_PERF_EVENTS
 	select HAVE_PERF_REGS
@@ -273,6 +273,9 @@ config AS_HAS_LBT_EXTENSION
 config AS_HAS_LVZ_EXTENSION
 	def_bool $(as-instr,hvcl 0)
 
+config AS_HAS_THIN_ADD_SUB
+	def_bool $(cc-option,-Wa$(comma)-mthin-add-sub) || CC_IS_CLANG
+
 menu "Kernel type and options"
 
 source "kernel/Kconfig.hz"
diff --git a/arch/loongarch/Kconfig.debug b/arch/loongarch/Kconfig.debug
index 98d60630c3d4..8b2ce5b5d43e 100644
--- a/arch/loongarch/Kconfig.debug
+++ b/arch/loongarch/Kconfig.debug
@@ -28,6 +28,7 @@ config UNWINDER_PROLOGUE
 
 config UNWINDER_ORC
 	bool "ORC unwinder"
+	depends on HAVE_OBJTOOL
 	select OBJTOOL
 	help
 	  This option enables the ORC (Oops Rewind Capability) unwinder for
-- 
2.45.2