[PATCH v14 09/19] unwind_user/sframe: Add support for outermost frame indication

[Jens Remus <jremus@linux.ibm.com>]

SFrame may represent an undefined return address (RA) as SFrame FRE
without any offsets as indication for an outermost frame.

Reviewed-by: Indu Bhagat <ibhagatgnu@gmail.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---
 kernel/unwind/sframe.c | 15 ++++++++++++++-
 kernel/unwind/sframe.h |  1 +
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index c60aa527984a..9c755965ab83 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -218,7 +218,7 @@ static __always_inline int __read_fre(struct sframe_section *sec,
 	UNSAFE_GET_USER_INC(info, cur, 1, Efault);
 	dataword_count = SFRAME_V3_FRE_DATAWORD_COUNT(info);
 	dataword_size  = dataword_size_enum_to_size(SFRAME_V3_FRE_DATAWORD_SIZE(info));
-	if (!dataword_count || !dataword_size)
+	if (!dataword_size)
 		return -EFAULT;
 
 	if (cur + (dataword_count * dataword_size) > sec->fres_end)
@@ -228,6 +228,17 @@ static __always_inline int __read_fre(struct sframe_section *sec,
 	if (fde_type != SFRAME_FDE_TYPE_DEFAULT)
 		return -EFAULT;
 
+	if (!dataword_count) {
+		/*
+		 * A FRE without data words indicates RA undefined /
+		 * outermost frame.
+		 */
+		cfa_off	= 0;
+		ra_off	= 0;
+		fp_off	= 0;
+		goto done;
+	}
+
 	UNSAFE_GET_USER_INC(cfa_off, cur, dataword_size, Efault);
 	dataword_count--;
 
@@ -248,6 +259,7 @@ static __always_inline int __read_fre(struct sframe_section *sec,
 	if (dataword_count)
 		return -EFAULT;
 
+done:
 	fre->size	= addr_size + 1 + (dataword_count * dataword_size);
 	fre->ip_off	= ip_off;
 	fre->cfa_off	= cfa_off;
@@ -314,6 +326,7 @@ static __always_inline int __find_fre(struct sframe_section *sec,
 	frame->ra_off  = fre->ra_off;
 	frame->fp_off  = fre->fp_off;
 	frame->use_fp  = SFRAME_V3_FRE_CFA_BASE_REG_ID(fre->info) == SFRAME_BASE_REG_FP;
+	frame->outermost = SFRAME_V3_FRE_RA_UNDEFINED_P(fre->info);
 
 	return 0;
 }
diff --git a/kernel/unwind/sframe.h b/kernel/unwind/sframe.h
index fc2908e92c7b..ed111fd0d702 100644
--- a/kernel/unwind/sframe.h
+++ b/kernel/unwind/sframe.h
@@ -77,5 +77,6 @@ struct sframe_fda_v3 {
 #define SFRAME_V3_FRE_DATAWORD_COUNT(info)		(((info) >> 1) & 0xf)
 #define SFRAME_V3_FRE_DATAWORD_SIZE(info)		(((info) >> 5) & 0x3)
 #define SFRAME_V3_AARCH64_FRE_MANGLED_RA_P(info)	(((info) >> 7) & 0x1)
+#define SFRAME_V3_FRE_RA_UNDEFINED_P(info)		(SFRAME_V3_FRE_DATAWORD_COUNT(info) == 0)
 
 #endif /* _SFRAME_H */
-- 
2.51.0