Enable architectures, such as s390, which store SFrame CFA offset values
encoded, to e.g. make (better) use of unsigned 8-bit SFrame offsets.

Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes in RFC v2:
    - Rename generic_sframe_cfa_offset_decode() to
      sframe_cfa_offset_decode(). (Josh)

 include/asm-generic/unwind_user_sframe.h | 8 ++++++++
 kernel/unwind/sframe.c                   | 2 ++
 2 files changed, 10 insertions(+)

diff --git a/include/asm-generic/unwind_user_sframe.h b/include/asm-generic/unwind_user_sframe.h
index 8c9ac47bc8bd..117b05e1dcab 100644
--- a/include/asm-generic/unwind_user_sframe.h
+++ b/include/asm-generic/unwind_user_sframe.h
@@ -9,4 +9,12 @@
 #define SFRAME_SP_OFFSET 0
 #endif
 
+#ifndef sframe_cfa_offset_decode
+static inline s32 sframe_cfa_offset_decode(s32 offset)
+{
+	return offset;
+}
+#define sframe_cfa_offset_decode sframe_cfa_offset_decode
+#endif
+
 #endif /* _ASM_GENERIC_UNWIND_USER_SFRAME_H */
diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index 6a6221ce6d12..5ac502f16bad 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -209,6 +209,7 @@ __read_regular_fre_datawords(struct sframe_section *sec,
 
 	UNSAFE_GET_USER_INC(cfa_off, cur, dataword_size, Efault);
 	dataword_count--;
+	cfa_off = sframe_cfa_offset_decode(cfa_off);
 
 	ra_off = sec->ra_off;
 	if (!ra_off && dataword_count) {
@@ -258,6 +259,7 @@ __read_flex_fde_fre_datawords(struct sframe_section *sec,
 	UNSAFE_GET_USER_INC(cfa_ctl, cur, dataword_size, Efault);
 	UNSAFE_GET_USER_INC(cfa_off, cur, dataword_size, Efault);
 	dataword_count -= 2;
+	cfa_off = sframe_cfa_offset_decode(cfa_off);
 
 	ra_off = sec->ra_off;
 	ra_ctl = ra_off ? 2 : 0; /* regnum=0, deref_p=(ra_off != 0), reg_p=0 */
-- 
2.51.0