[tip: objtool/urgent] objtool/loongarch: Add unwind hints in prepare_frametrace()

["tip-bot2 for Josh Poimboeuf" <tip-bot2@linutronix.de>]

The following commit has been merged into the objtool/urgent branch of tip:

Commit-ID:     7c977393b8277ed319e92e4b598b26598c9d30c0
Gitweb:        https://git.kernel.org/tip/7c977393b8277ed319e92e4b598b26598c9d30c0
Author:        Josh Poimboeuf <jpoimboe@kernel.org>
AuthorDate:    Mon, 31 Mar 2025 21:26:43 -07:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 01 Apr 2025 10:10:10 +02:00

objtool/loongarch: Add unwind hints in prepare_frametrace()

If 'regs' points to a local stack variable, prepare_frametrace() stores
all registers to the stack.  This confuses objtool as it expects them to
be restored from the stack later.

The stores don't affect stack tracing, so use unwind hints to hide them
from objtool.

Fixes the following warnings:

  arch/loongarch/kernel/traps.o: warning: objtool: show_stack+0xe0: stack state mismatch: reg1[22]=-1+0 reg2[22]=-2-160
  arch/loongarch/kernel/traps.o: warning: objtool: show_stack+0xe0: stack state mismatch: reg1[23]=-1+0 reg2[23]=-2-152

Fixes: cb8a2ef0848c ("LoongArch: Add ORC stack unwinder support")
Reported-by: kernel test robot <lkp@intel.com>
Tested-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/270cadd8040dda74db2307f23497bb68e65db98d.1743481539.git.jpoimboe@kernel.org
Closes: https://lore.kernel.org/oe-kbuild-all/202503280703.OARM8SrY-lkp@intel.com/
---
 arch/loongarch/include/asm/stacktrace.h   |  3 +++
 arch/loongarch/include/asm/unwind_hints.h | 10 +++++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/loongarch/include/asm/stacktrace.h b/arch/loongarch/include/asm/stacktrace.h
index f23adb1..fc8b647 100644
--- a/arch/loongarch/include/asm/stacktrace.h
+++ b/arch/loongarch/include/asm/stacktrace.h
@@ -8,6 +8,7 @@
 #include <asm/asm.h>
 #include <asm/ptrace.h>
 #include <asm/loongarch.h>
+#include <asm/unwind_hints.h>
 #include <linux/stringify.h>
 
 enum stack_type {
@@ -43,6 +44,7 @@ int get_stack_info(unsigned long stack, struct task_struct *task, struct stack_i
 static __always_inline void prepare_frametrace(struct pt_regs *regs)
 {
 	__asm__ __volatile__(
+		UNWIND_HINT_SAVE
 		/* Save $ra */
 		STORE_ONE_REG(1)
 		/* Use $ra to save PC */
@@ -80,6 +82,7 @@ static __always_inline void prepare_frametrace(struct pt_regs *regs)
 		STORE_ONE_REG(29)
 		STORE_ONE_REG(30)
 		STORE_ONE_REG(31)
+		UNWIND_HINT_RESTORE
 		: "=m" (regs->csr_era)
 		: "r" (regs->regs)
 		: "memory");
diff --git a/arch/loongarch/include/asm/unwind_hints.h b/arch/loongarch/include/asm/unwind_hints.h
index a01086a..2c68bc7 100644
--- a/arch/loongarch/include/asm/unwind_hints.h
+++ b/arch/loongarch/include/asm/unwind_hints.h
@@ -23,6 +23,14 @@
 	UNWIND_HINT sp_reg=ORC_REG_SP type=UNWIND_HINT_TYPE_CALL
 .endm
 
-#endif /* __ASSEMBLY__ */
+#else /* !__ASSEMBLY__ */
+
+#define UNWIND_HINT_SAVE \
+	UNWIND_HINT(UNWIND_HINT_TYPE_SAVE, 0, 0, 0)
+
+#define UNWIND_HINT_RESTORE \
+	UNWIND_HINT(UNWIND_HINT_TYPE_RESTORE, 0, 0, 0)
+
+#endif /* !__ASSEMBLY__ */
 
 #endif /* _ASM_LOONGARCH_UNWIND_HINTS_H */