[RFC PATCH v1 09/16] unwind_user/sframe: Enable archs with encoded SFrame CFA offsets

[Jens Remus]

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@xxxxxxxxxxxxx>
---
 include/asm-generic/unwind_user_sframe.h | 11 +++++++++++
 kernel/unwind/sframe.c                   |  1 +
 2 files changed, 12 insertions(+)

diff --git a/include/asm-generic/unwind_user_sframe.h b/include/asm-generic/unwind_user_sframe.h
index 8cef3e0857b6..cea0410a259a 100644
--- a/include/asm-generic/unwind_user_sframe.h
+++ b/include/asm-generic/unwind_user_sframe.h
@@ -5,6 +5,16 @@
 #include <linux/unwind_user_types.h>
 #include <linux/types.h>
 
+/**
+ * generic_sframe_cfa_offset_decode - Decode SFrame CFA offset.
+ *
+ * Returns the decoded SFrame CFA offset value.
+ */
+static inline s32 generic_sframe_cfa_offset_decode(s32 offset)
+{
+	return offset;
+}
+
 /**
  * generic_sframe_set_frame_reginfo - Populate info to unwind FP/RA register
  * from SFrame offset.
@@ -48,6 +58,7 @@ static inline s32 generic_sframe_sp_val_off(void)
 	return 0;
 }
 
+#define sframe_cfa_offset_decode generic_sframe_cfa_offset_decode
 #define sframe_set_frame_reginfo generic_sframe_set_frame_reginfo
 #define sframe_sp_val_off generic_sframe_sp_val_off
 
diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index 43ef3a8c4c26..e8658401a286 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -220,6 +220,7 @@ static __always_inline int __read_fre(struct sframe_section *sec,
 
 	UNSAFE_GET_USER_INC(cfa_off, cur, offset_size, Efault);
 	offset_count--;
+	cfa_off = sframe_cfa_offset_decode(cfa_off);
 
 	ra_off = sec->ra_off;
 	if (!ra_off && offset_count) {
-- 
2.48.1