[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20250901072156.31361-4-yangtiezhu@loongson.cn>
Date: Mon, 1 Sep 2025 15:21:56 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>,
Josh Poimboeuf <jpoimboe@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Nathan Chancellor <nathan@...nel.org>
Cc: loongarch@...ts.linux.dev,
linux-kernel@...r.kernel.org
Subject: [PATCH v1 3/3] LoongArch: Fix unreachable instruction warnings about entry functions
When compiling with LLVM and CONFIG_LTO_CLANG is set, there exist the
following objtool warnings:
vmlinux.o: warning: objtool: kernel_entry+0x0: unreachable instruction
vmlinux.o: warning: objtool: smpboot_entry+0x0: unreachable instruction
kernel_entry() and smpboot_entry() are in arch/loongarch/kernel/head.S,
there is "OBJECT_FILES_NON_STANDARD_head.o := y" to skip objtool checking
for head.o, but the STACK_FRAME_NON_STANDARD macro does not work for link
time validation of vmlinux.o according to objtool documentation, just give
a proper unwind hint to silence the warnings.
By the way, ASM_BUG() can be removed due to unnecessary, otherwise there
are following warnings:
kernel_entry+0xf4: start_kernel() missing __noreturn
in .c/.h or NORETURN() in noreturns.h
smpboot_entry+0x68: start_secondary() missing __noreturn
in .c/.h or NORETURN() in noreturns.h
This is because the previous instructions of kernel_entry+0xf4 and
smpboot_entry+0x68 are the 'bl' instructions, start_kernel() and
start_secondary() are the respective call destination symbols which
are noreturn functions, then the 'bl' instructions are already marked
as dead end in annotate_call_site().
For now, it is time to remove "OBJECT_FILES_NON_STANDARD_head.o := y"
in arch/loongarch/kernel/Makefile.
Link: https://lore.kernel.org/lkml/20250814083651.GR4067720@noisy.programming.kicks-ass.net/
Suggested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
---
arch/loongarch/kernel/Makefile | 2 --
arch/loongarch/kernel/head.S | 6 ++----
2 files changed, 2 insertions(+), 6 deletions(-)
diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
index 6f5a4574a911..4302c5b0a201 100644
--- a/arch/loongarch/kernel/Makefile
+++ b/arch/loongarch/kernel/Makefile
@@ -3,8 +3,6 @@
# Makefile for the Linux/LoongArch kernel.
#
-OBJECT_FILES_NON_STANDARD_head.o := y
-
always-$(KBUILD_BUILTIN) := vmlinux.lds
obj-y += head.o cpu-probe.o cacheinfo.o env.o setup.o entry.o genex.o \
diff --git a/arch/loongarch/kernel/head.S b/arch/loongarch/kernel/head.S
index e3865e92a917..a11880f3a7e1 100644
--- a/arch/loongarch/kernel/head.S
+++ b/arch/loongarch/kernel/head.S
@@ -42,6 +42,7 @@ SYM_DATA(kernel_fsize, .long _kernel_fsize);
.align 12
SYM_CODE_START(kernel_entry) # kernel entry point
+ UNWIND_HINT_UNDEFINED
/* Config direct window and set PG */
SETUP_DMWINS t0
@@ -109,8 +110,6 @@ SYM_CODE_START(kernel_entry) # kernel entry point
#endif
bl start_kernel
- ASM_BUG()
-
SYM_CODE_END(kernel_entry)
#ifdef CONFIG_SMP
@@ -120,6 +119,7 @@ SYM_CODE_END(kernel_entry)
* function after setting up the stack and tp registers.
*/
SYM_CODE_START(smpboot_entry)
+ UNWIND_HINT_UNDEFINED
SETUP_DMWINS t0
JUMP_VIRT_ADDR t0, t1
@@ -142,8 +142,6 @@ SYM_CODE_START(smpboot_entry)
ld.d tp, t0, CPU_BOOT_TINFO
bl start_secondary
- ASM_BUG()
-
SYM_CODE_END(smpboot_entry)
#endif /* CONFIG_SMP */
--
2.42.0
Powered by blists - more mailing lists