linux-kernel - [PATCH v1] LoongArch: Add -fno-isolate-erroneous-paths-dereference in Makefile

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Message-ID: <20250923061722.24457-1-yangtiezhu@loongson.cn>
Date: Tue, 23 Sep 2025 14:17:22 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: WANG Rui <wangrui@...ngson.cn>,
	loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [PATCH v1] LoongArch: Add -fno-isolate-erroneous-paths-dereference in Makefile

Currently, when compiling with GCC, there is no "break 0x7" instruction
for zero division due to using the option -mno-check-zero-division, but
the compiler still generates "break 0x0" instruction for zero division.

Here is a simple example:

  $ cat test.c
  int div(int a)
  {
	  return a / 0;
  }
  $ gcc -O2 -S test.c -o test.s

GCC generates "break 0" On LoongArch and "ud2" on x86, objtool decodes
"ud2" as INSN_BUG for x86, so decode "break 0" as INSN_BUG can fix the
objtool warnings for LoongArch, but this is not the intention.

When decoding "break 0" as INSN_TRAP in the previous commit, the aim is
to handle "break 0" as a trap. The generated "break 0" for zero division
by GCC is not proper, it should generate a break instruction with proper
bug type, so add the GCC option -fno-isolate-erroneous-paths-dereference
to avoid generating the unexpected "break 0" instruction for now.

Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/r/202509200413.7uihAxJ5-lkp@intel.com/
Fixes: baad7830ee9a ("objtool/LoongArch: Mark types based on break immediate code")
Suggested-by: WANG Rui <wangrui@...ngson.cn>
Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
---
 arch/loongarch/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
index ae419e32f22e..f2a585b4a937 100644
--- a/arch/loongarch/Makefile
+++ b/arch/loongarch/Makefile
@@ -129,7 +129,7 @@ KBUILD_RUSTFLAGS_KERNEL		+= -Crelocation-model=pie
 LDFLAGS_vmlinux			+= -static -pie --no-dynamic-linker -z notext $(call ld-option, --apply-dynamic-relocs)
 endif

-cflags-y += $(call cc-option, -mno-check-zero-division)
+cflags-y += $(call cc-option, -mno-check-zero-division -fno-isolate-erroneous-paths-dereference)

 ifndef CONFIG_KASAN
 cflags-y += -fno-builtin-memcpy -fno-builtin-memmove -fno-builtin-memset
-- 
2.42.0