[PATCH v7 06/22] perf arm-spe: Refactor printing string to buffer

[Leo Yan]

When outputs strings to the decoding buffer with function snprintf(),
SPE decoder needs to detects if any error returns from snprintf() and if
so needs to directly bail out.  If snprintf() returns success, it needs
to update buffer pointer and reduce the buffer length so can continue to
output the next string into the consequent memory space.

This complex logics are spreading in the function arm_spe_pkt_desc() so
there has many duplicate codes for handling error detecting, increment
buffer pointer and decrement buffer size.

To avoid the duplicate code, this patch introduces a new helper function
arm_spe_pkt_snprintf() which is used to wrap up the complex logics, and
it's used by the caller arm_spe_pkt_desc().

This patch also moves the variable 'blen' as the function's local
variable, this allows to remove the unnecessary braces and improve the
readability.

Suggested-by: Dave Martin <Dave.Martin@xxxxxxx>
Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
---
 .../arm-spe-decoder/arm-spe-pkt-decoder.c     | 260 +++++++++---------
 1 file changed, 126 insertions(+), 134 deletions(-)

diff --git a/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c b/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c
index 04fd7fd7c15f..1970686f7020 100644
--- a/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c
+++ b/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c
@@ -9,6 +9,7 @@
 #include <endian.h>
 #include <byteswap.h>
 #include <linux/bitops.h>
+#include <stdarg.h>
 
 #include "arm-spe-pkt-decoder.h"
 
@@ -258,192 +259,183 @@ int arm_spe_get_packet(const unsigned char *buf, size_t len,
 	return ret;
 }
 
+static int arm_spe_pkt_snprintf(int *err, char **buf_p, size_t *blen,
+				const char *fmt, ...)
+{
+	va_list ap;
+	int ret;
+
+	/* Bail out if any error occurred */
+	if (err && *err)
+		return *err;
+
+	va_start(ap, fmt);
+	ret = vsnprintf(*buf_p, *blen, fmt, ap);
+	va_end(ap);
+
+	if (ret < 0) {
+		if (err && !*err)
+			*err = ret;
+
+	/*
+	 * A return value of (*blen - 1) or more means that the
+	 * output was truncated and the buffer is overrun.
+	 */
+	} else if (ret >= ((int)*blen - 1)) {
+		(*buf_p)[*blen - 1] = '\0';
+
+		/*
+		 * Set *err to 'ret' to avoid overflow if tries to
+		 * fill this buffer sequentially.
+		 */
+		if (err && !*err)
+			*err = ret;
+	} else {
+		*buf_p += ret;
+		*blen -= ret;
+	}
+
+	return ret;
+}
+
 int arm_spe_pkt_desc(const struct arm_spe_pkt *packet, char *buf,
 		     size_t buf_len)
 {
 	int ret, ns, el, idx = packet->index;
 	unsigned long long payload = packet->payload;
 	const char *name = arm_spe_pkt_name(packet->type);
+	size_t blen = buf_len;
+	int err = 0;
 
 	switch (packet->type) {
 	case ARM_SPE_BAD:
 	case ARM_SPE_PAD:
 	case ARM_SPE_END:
-		return snprintf(buf, buf_len, "%s", name);
-	case ARM_SPE_EVENTS: {
-		size_t blen = buf_len;
-
-		ret = 0;
-		ret = snprintf(buf, buf_len, "EV");
-		buf += ret;
-		blen -= ret;
-		if (payload & 0x1) {
-			ret = snprintf(buf, buf_len, " EXCEPTION-GEN");
-			buf += ret;
-			blen -= ret;
-		}
-		if (payload & 0x2) {
-			ret = snprintf(buf, buf_len, " RETIRED");
-			buf += ret;
-			blen -= ret;
-		}
-		if (payload & 0x4) {
-			ret = snprintf(buf, buf_len, " L1D-ACCESS");
-			buf += ret;
-			blen -= ret;
-		}
-		if (payload & 0x8) {
-			ret = snprintf(buf, buf_len, " L1D-REFILL");
-			buf += ret;
-			blen -= ret;
-		}
-		if (payload & 0x10) {
-			ret = snprintf(buf, buf_len, " TLB-ACCESS");
-			buf += ret;
-			blen -= ret;
-		}
-		if (payload & 0x20) {
-			ret = snprintf(buf, buf_len, " TLB-REFILL");
-			buf += ret;
-			blen -= ret;
-		}
-		if (payload & 0x40) {
-			ret = snprintf(buf, buf_len, " NOT-TAKEN");
-			buf += ret;
-			blen -= ret;
-		}
-		if (payload & 0x80) {
-			ret = snprintf(buf, buf_len, " MISPRED");
-			buf += ret;
-			blen -= ret;
-		}
+		return arm_spe_pkt_snprintf(&err, &buf, &blen, "%s", name);
+	case ARM_SPE_EVENTS:
+		ret = arm_spe_pkt_snprintf(&err, &buf, &blen, "EV");
+
+		if (payload & 0x1)
+			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " EXCEPTION-GEN");
+		if (payload & 0x2)
+			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " RETIRED");
+		if (payload & 0x4)
+			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " L1D-ACCESS");
+		if (payload & 0x8)
+			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " L1D-REFILL");
+		if (payload & 0x10)
+			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " TLB-ACCESS");
+		if (payload & 0x20)
+			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " TLB-REFILL");
+		if (payload & 0x40)
+			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " NOT-TAKEN");
+		if (payload & 0x80)
+			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " MISPRED");
 		if (idx > 1) {
-			if (payload & 0x100) {
-				ret = snprintf(buf, buf_len, " LLC-ACCESS");
-				buf += ret;
-				blen -= ret;
-			}
-			if (payload & 0x200) {
-				ret = snprintf(buf, buf_len, " LLC-REFILL");
-				buf += ret;
-				blen -= ret;
-			}
-			if (payload & 0x400) {
-				ret = snprintf(buf, buf_len, " REMOTE-ACCESS");
-				buf += ret;
-				blen -= ret;
-			}
+			if (payload & 0x100)
+				ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " LLC-ACCESS");
+			if (payload & 0x200)
+				ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " LLC-REFILL");
+			if (payload & 0x400)
+				ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " REMOTE-ACCESS");
 		}
 		if (ret < 0)
 			return ret;
 		blen -= ret;
 		return buf_len - blen;
-	}
 	case ARM_SPE_OP_TYPE:
 		switch (idx) {
-		case 0:	return snprintf(buf, buf_len, "%s", payload & 0x1 ?
-					"COND-SELECT" : "INSN-OTHER");
-		case 1:	{
-			size_t blen = buf_len;
+		case 0:
+			return arm_spe_pkt_snprintf(&err, &buf, &blen,
+					payload & 0x1 ? "COND-SELECT" : "INSN-OTHER");
+		case 1:
+			ret = arm_spe_pkt_snprintf(&err, &buf, &blen,
+						   payload & 0x1 ? "ST" : "LD");
 
-			if (payload & 0x1)
-				ret = snprintf(buf, buf_len, "ST");
-			else
-				ret = snprintf(buf, buf_len, "LD");
-			buf += ret;
-			blen -= ret;
 			if (payload & 0x2) {
-				if (payload & 0x4) {
-					ret = snprintf(buf, buf_len, " AT");
-					buf += ret;
-					blen -= ret;
-				}
-				if (payload & 0x8) {
-					ret = snprintf(buf, buf_len, " EXCL");
-					buf += ret;
-					blen -= ret;
-				}
-				if (payload & 0x10) {
-					ret = snprintf(buf, buf_len, " AR");
-					buf += ret;
-					blen -= ret;
-				}
+				if (payload & 0x4)
+					ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " AT");
+				if (payload & 0x8)
+					ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " EXCL");
+				if (payload & 0x10)
+					ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " AR");
 			} else if (payload & 0x4) {
-				ret = snprintf(buf, buf_len, " SIMD-FP");
-				buf += ret;
-				blen -= ret;
+				ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " SIMD-FP");
 			}
+
 			if (ret < 0)
 				return ret;
 			blen -= ret;
 			return buf_len - blen;
-		}
-		case 2:	{
-			size_t blen = buf_len;
 
-			ret = snprintf(buf, buf_len, "B");
-			buf += ret;
-			blen -= ret;
-			if (payload & 0x1) {
-				ret = snprintf(buf, buf_len, " COND");
-				buf += ret;
-				blen -= ret;
-			}
-			if (payload & 0x2) {
-				ret = snprintf(buf, buf_len, " IND");
-				buf += ret;
-				blen -= ret;
-			}
+		case 2:
+			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, "B");
+
+			if (payload & 0x1)
+				ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " COND");
+			if (payload & 0x2)
+				ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " IND");
+
 			if (ret < 0)
 				return ret;
 			blen -= ret;
 			return buf_len - blen;
-			}
-		default: return 0;
+
+		default:
+			return 0;
 		}
 	case ARM_SPE_DATA_SOURCE:
 	case ARM_SPE_TIMESTAMP:
-		return snprintf(buf, buf_len, "%s %lld", name, payload);
+		return arm_spe_pkt_snprintf(&err, &buf, &blen, "%s %lld", name, payload);
 	case ARM_SPE_ADDRESS:
 		switch (idx) {
 		case 0:
-		case 1: ns = !!(packet->payload & NS_FLAG);
+		case 1:
+			ns = !!(packet->payload & NS_FLAG);
 			el = (packet->payload & EL_FLAG) >> 61;
 			payload &= ~(0xffULL << 56);
-			return snprintf(buf, buf_len, "%s 0x%llx el%d ns=%d",
+			return arm_spe_pkt_snprintf(&err, &buf, &blen,
+					"%s 0x%llx el%d ns=%d",
 				        (idx == 1) ? "TGT" : "PC", payload, el, ns);
-		case 2:	return snprintf(buf, buf_len, "VA 0x%llx", payload);
-		case 3:	ns = !!(packet->payload & NS_FLAG);
+		case 2:
+			return arm_spe_pkt_snprintf(&err, &buf, &blen,
+						    "VA 0x%llx", payload);
+		case 3:
+			ns = !!(packet->payload & NS_FLAG);
 			payload &= ~(0xffULL << 56);
-			return snprintf(buf, buf_len, "PA 0x%llx ns=%d",
-					payload, ns);
-		default: return 0;
+			return arm_spe_pkt_snprintf(&err, &buf, &blen,
+						    "PA 0x%llx ns=%d", payload, ns);
+		default:
+			return 0;
 		}
 	case ARM_SPE_CONTEXT:
-		return snprintf(buf, buf_len, "%s 0x%lx el%d", name,
-				(unsigned long)payload, idx + 1);
-	case ARM_SPE_COUNTER: {
-		size_t blen = buf_len;
-
-		ret = snprintf(buf, buf_len, "%s %d ", name,
-			       (unsigned short)payload);
-		buf += ret;
-		blen -= ret;
+		return arm_spe_pkt_snprintf(&err, &buf, &blen, "%s 0x%lx el%d",
+					    name, (unsigned long)payload, idx + 1);
+	case ARM_SPE_COUNTER:
+		ret = arm_spe_pkt_snprintf(&err, &buf, &blen, "%s %d ", name,
+					   (unsigned short)payload);
 		switch (idx) {
-		case 0:	ret = snprintf(buf, buf_len, "TOT"); break;
-		case 1:	ret = snprintf(buf, buf_len, "ISSUE"); break;
-		case 2:	ret = snprintf(buf, buf_len, "XLAT"); break;
-		default: ret = 0;
+		case 0:
+			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, "TOT");
+			break;
+		case 1:
+			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, "ISSUE");
+			break;
+		case 2:
+			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, "XLAT");
+			break;
+		default:
+			ret = 0;
+			break;
 		}
 		if (ret < 0)
 			return ret;
 		blen -= ret;
 		return buf_len - blen;
-	}
 	default:
 		break;
 	}
 
-	return snprintf(buf, buf_len, "%s 0x%llx (%d)",
-			name, payload, packet->index);
+	return arm_spe_pkt_snprintf(&err, &buf, &blen, "%s 0x%llx (%d)",
+				    name, payload, packet->index);
 }
-- 
2.17.1