[PATCH v8 04/11] sframe: Separate reading of FRE from reading of FRE data words

[Dylan Hatch <dylanbhatch@google.com>]

From: Jens Remus <jremus@linux.ibm.com>

__find_fre() performs linear search for a matching SFrame FRE for a
given IP.  For that purpose it uses __read_fre(), which reads the whole
FRE.  That is the variable-size FRE structure as well as the trailing
variable-length array of variable-size data words.  For the search logic
to skip over the FRE it would be sufficient to read the variable-size
FRE structure only, which includes the count and size of data words.

Add fields to struct sframe_fre_internal to store the FRE data word's
address, count, and size.  Change __read_fre() to read the variable-
size FRE structure only and populate those new fields.  Change
__read_fre_datawords() to use those new fields.  Change __find_fre()
to use __read_fre_datawords() to read the FRE data words only after a
matching FRE has been found.

[ Dylan Hatch: Adapt for in-kernel unwinding without flexible FDEs. ]

Reviewed-by: Indu Bhagat <ibhagatgnu@gmail.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Dylan Hatch <dylanbhatch@google.com>
---
 kernel/unwind/sframe.c | 97 +++++++++++++++++++++++++++++++-----------
 1 file changed, 73 insertions(+), 24 deletions(-)

diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index 2a188373be857..ec81110a36796 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -37,6 +37,9 @@ struct sframe_fre_internal {
 	s32		ra_off;
 	s32		fp_off;
 	u8		info;
+	unsigned long	dw_addr;
+	unsigned char	dw_count;
+	unsigned char	dw_size;
 };
 
 static __always_inline unsigned char fre_type_to_size(unsigned char fre_type)
@@ -180,6 +183,67 @@ static __always_inline int __find_fde(struct sframe_section *sec,
 		 s32 :	GET_SIGNED_AND_INC(to, from, size),	\
 		 s64 :	GET_SIGNED_AND_INC(to, from, size))
 
+static __always_inline int
+__read_default_fre_datawords(struct sframe_section *sec,
+			     struct sframe_fde_internal *fde,
+			     struct sframe_fre_internal *fre)
+{
+	unsigned char dataword_count = fre->dw_count;
+	unsigned char dataword_size = fre->dw_size;
+	unsigned long cur = fre->dw_addr;
+	s32 cfa_off, ra_off, fp_off;
+
+	GET_AND_INC(cfa_off, cur, dataword_size);
+	dataword_count--;
+
+	ra_off = sec->ra_off;
+	if (!ra_off && dataword_count) {
+		dataword_count--;
+		GET_AND_INC(ra_off, cur, dataword_size);
+	}
+
+	fp_off = sec->fp_off;
+	if (!fp_off && dataword_count) {
+		dataword_count--;
+		GET_AND_INC(fp_off, cur, dataword_size);
+	}
+
+	if (dataword_count)
+		return -EFAULT;
+
+	fre->cfa_off	= cfa_off;
+	fre->ra_off	= ra_off;
+	fre->fp_off	= fp_off;
+
+	return 0;
+}
+
+static __always_inline int
+__read_fre_datawords(struct sframe_section *sec,
+		     struct sframe_fde_internal *fde,
+		     struct sframe_fre_internal *fre)
+{
+	unsigned char fde_type = SFRAME_V3_FDE_TYPE(fde->info2);
+	unsigned char dataword_count = fre->dw_count;
+
+	if (!dataword_count) {
+		/* A FRE without data words indicates an outermost frame. */
+		fre->cfa_off	= 0;
+		fre->ra_off	= 0;
+		fre->fp_off	= 0;
+
+		return 0;
+	}
+
+	switch (fde_type) {
+	case SFRAME_FDE_TYPE_DEFAULT:
+		return __read_default_fre_datawords(sec, fde, fre);
+	/* Flexible FDEs not supported */
+	default:
+		return -EFAULT;
+	}
+}
+
 static __always_inline int __read_fre(struct sframe_section *sec,
 				      struct sframe_fde_internal *fde,
 				      unsigned long fre_addr,
@@ -189,7 +253,6 @@ static __always_inline int __read_fre(struct sframe_section *sec,
 	unsigned char fde_pctype = SFRAME_V3_FDE_PCTYPE(fde->info);
 	unsigned char fre_type = SFRAME_V3_FDE_FRE_TYPE(fde->info);
 	unsigned char dataword_count, dataword_size;
-	s32 cfa_off, ra_off, fp_off;
 	unsigned long cur = fre_addr;
 	unsigned char addr_size;
 	u32 ip_off;
@@ -209,7 +272,7 @@ static __always_inline int __read_fre(struct sframe_section *sec,
 	GET_AND_INC(info, cur, 1);
 	dataword_count = SFRAME_V3_FRE_DATAWORD_COUNT(info);
 	dataword_size  = dataword_size_enum_to_size(SFRAME_V3_FRE_DATAWORD_SIZE(info));
-	if (!dataword_size || !dataword_count)
+	if (!dataword_size)
 		return -EFAULT;
 
 	if (cur + (dataword_count * dataword_size) > sec->fres_end)
@@ -220,30 +283,11 @@ static __always_inline int __read_fre(struct sframe_section *sec,
 		return -EFAULT;
 
 	fre->size	= addr_size + 1 + (dataword_count * dataword_size);
-
-	GET_AND_INC(cfa_off, cur, dataword_size);
-	dataword_count--;
-
-	ra_off = sec->ra_off;
-	if (!ra_off && dataword_count) {
-		dataword_count--;
-		GET_AND_INC(ra_off, cur, dataword_size);
-	}
-
-	fp_off = sec->fp_off;
-	if (!fp_off && dataword_count) {
-		dataword_count--;
-		GET_AND_INC(fp_off, cur, dataword_size);
-	}
-
-	if (dataword_count)
-		return -EFAULT;
-
 	fre->ip_off	= ip_off;
-	fre->cfa_off	= cfa_off;
-	fre->ra_off	= ra_off;
-	fre->fp_off	= fp_off;
 	fre->info	= info;
+	fre->dw_addr	= cur;
+	fre->dw_count	= dataword_count;
+	fre->dw_size	= dataword_size;
 
 	return 0;
 }
@@ -293,6 +337,7 @@ static __always_inline int __find_fre(struct sframe_section *sec,
 	bool which = false;
 	unsigned int i;
 	u32 ip_off;
+	int ret;
 
 	ip_off = ip - fde->func_addr;
 
@@ -333,6 +378,10 @@ static __always_inline int __find_fre(struct sframe_section *sec,
 		return -EINVAL;
 	fre = prev_fre;
 
+	ret = __read_fre_datawords(sec, fde, fre);
+	if (ret)
+		return ret;
+
 	if (sframe_init_cfa_rule_data(&frame->cfa, fre->info, fre->cfa_off))
 		return -EINVAL;
 
-- 
2.56.0.360.g66cac248cb-goog