Add a signal flag to struct unwind_user_frame, which indicates whether
the frame is a signal frame.  If set unwind_user_common_next() uses an
architecture-specific unwind_user_signal_next() implementation to
unwind the frame.

user unwind sframe will make use of the signal flag in a subsequent
commit.

Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---
 arch/x86/include/asm/unwind_user.h | 6 ++++--
 include/linux/unwind_user.h        | 9 +++++++++
 include/linux/unwind_user_types.h  | 1 +
 kernel/unwind/user.c               | 4 ++++
 4 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/unwind_user.h b/arch/x86/include/asm/unwind_user.h
index f5e9fbcdae28..21cb9eeb2503 100644
--- a/arch/x86/include/asm/unwind_user.h
+++ b/arch/x86/include/asm/unwind_user.h
@@ -67,7 +67,8 @@ static inline int unwind_user_get_reg(unsigned long *val, unsigned int regnum)
 		.offset		= -2*(ws),		\
 			},				\
 	.sp_off		= 0,				\
-	.outermost	= false,
+	.outermost	= false,			\
+	.signal		= false,
 
 #define ARCH_INIT_USER_FP_ENTRY_FRAME(ws)		\
 	.cfa		= {				\
@@ -82,7 +83,8 @@ static inline int unwind_user_get_reg(unsigned long *val, unsigned int regnum)
 		.rule		= UNWIND_USER_RULE_RETAIN,\
 			},				\
 	.sp_off		= 0,				\
-	.outermost	= false,
+	.outermost	= false,			\
+	.signal		= false,
 
 static inline int unwind_user_fp_get_frame(struct unwind_user_state *state,
 					   struct unwind_user_frame *frame)
diff --git a/include/linux/unwind_user.h b/include/linux/unwind_user.h
index f65b0573b3a5..eb5de4cb5bd6 100644
--- a/include/linux/unwind_user.h
+++ b/include/linux/unwind_user.h
@@ -34,6 +34,15 @@ static inline int unwind_user_get_reg(unsigned long *val, unsigned int regnum)
 #define unwind_user_get_reg unwind_user_get_reg
 #endif
 
+#ifndef unwind_user_signal_next
+static inline int unwind_user_signal_next(struct unwind_user_state *state)
+{
+	WARN_ON_ONCE(1);
+	return -EINVAL;
+}
+#define unwind_user_signal_next unwind_user_signal_next
+#endif
+
 int unwind_user(struct unwind_stacktrace *trace, unsigned int max_entries);
 
 #endif /* _LINUX_UNWIND_USER_H */
diff --git a/include/linux/unwind_user_types.h b/include/linux/unwind_user_types.h
index fac8f470b597..3985706d7851 100644
--- a/include/linux/unwind_user_types.h
+++ b/include/linux/unwind_user_types.h
@@ -68,6 +68,7 @@ struct unwind_user_frame {
 	struct unwind_user_rule_data fp;
 	s32 sp_off;
 	bool outermost;
+	bool signal;
 };
 
 struct unwind_user_state {
diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
index a64ceb4a2bf6..b9a3b59e8282 100644
--- a/kernel/unwind/user.c
+++ b/kernel/unwind/user.c
@@ -32,6 +32,10 @@ static int unwind_user_next_common(struct unwind_user_state *state,
 {
 	unsigned long cfa, sp, fp, ra;
 
+	/* Use signal frame unwinder for signal frames. */
+	if (frame->signal)
+		return unwind_user_signal_next(state);
+
 	/* Stop unwinding when reaching an outermost frame. */
 	if (frame->outermost) {
 		state->done = true;
-- 
2.51.0