[PATCH v9 01/16] perf arm-spe: Refactor printing string to buffer

[Leo Yan <leo.yan@linaro.org>]

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_out_string() which is used to wrap up the complex logics,
and it's used by the caller arm_spe_pkt_desc().  This patch moves the
variable 'blen' as the function's local variable so allows to remove
the unnecessary braces and improve the readability.

This patch simplifies the return value for arm_spe_pkt_desc(): '0' means
success and other values mean an error has occurred.  To realize this,
it relies on arm_spe_pkt_out_string()'s parameter 'err', the 'err' is a
cumulative value, returns its final value if printing buffer is called
for one time or multiple times.  Finally, the error is handled in a
central place, rather than directly bailing out in switch-cases, it
returns error at the end of arm_spe_pkt_desc().

This patch changes the caller arm_spe_dump() to respect the updated
return value semantics of arm_spe_pkt_desc().

Suggested-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
---
 .../arm-spe-decoder/arm-spe-pkt-decoder.c     | 302 +++++++++---------
 tools/perf/util/arm-spe.c                     |   2 +-
 2 files changed, 151 insertions(+), 153 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 671a4763fb47..fbededc1bcd4 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 +259,189 @@ int arm_spe_get_packet(const unsigned char *buf, size_t len,
 	return ret;
 }
 
+static int arm_spe_pkt_out_string(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 or more means that the output was
+	 * truncated and the buffer is overrun.
+	 */
+	} else if ((size_t)ret >= *blen) {
+		(*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;
+	int ns, el, idx = packet->index;
 	unsigned long long payload = packet->payload;
 	const char *name = arm_spe_pkt_name(packet->type);
+	char *buf_orig = buf;
+	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;
-		}
+		arm_spe_pkt_out_string(&err, &buf, &blen, "%s", name);
+		break;
+	case ARM_SPE_EVENTS:
+		arm_spe_pkt_out_string(&err, &buf, &blen, "EV");
+
+		if (payload & 0x1)
+			arm_spe_pkt_out_string(&err, &buf, &blen, " EXCEPTION-GEN");
+		if (payload & 0x2)
+			arm_spe_pkt_out_string(&err, &buf, &blen, " RETIRED");
+		if (payload & 0x4)
+			arm_spe_pkt_out_string(&err, &buf, &blen, " L1D-ACCESS");
+		if (payload & 0x8)
+			arm_spe_pkt_out_string(&err, &buf, &blen, " L1D-REFILL");
+		if (payload & 0x10)
+			arm_spe_pkt_out_string(&err, &buf, &blen, " TLB-ACCESS");
+		if (payload & 0x20)
+			arm_spe_pkt_out_string(&err, &buf, &blen, " TLB-REFILL");
+		if (payload & 0x40)
+			arm_spe_pkt_out_string(&err, &buf, &blen, " NOT-TAKEN");
+		if (payload & 0x80)
+			arm_spe_pkt_out_string(&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)
+				arm_spe_pkt_out_string(&err, &buf, &blen, " LLC-ACCESS");
+			if (payload & 0x200)
+				arm_spe_pkt_out_string(&err, &buf, &blen, " LLC-REFILL");
+			if (payload & 0x400)
+				arm_spe_pkt_out_string(&err, &buf, &blen, " REMOTE-ACCESS");
 		}
-		if (ret < 0)
-			return ret;
-		blen -= ret;
-		return buf_len - blen;
-	}
+		break;
 	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:
+			arm_spe_pkt_out_string(&err, &buf, &blen,
+					payload & 0x1 ? "COND-SELECT" : "INSN-OTHER");
+			break;
+		case 1:
+			arm_spe_pkt_out_string(&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)
+					arm_spe_pkt_out_string(&err, &buf, &blen, " AT");
+				if (payload & 0x8)
+					arm_spe_pkt_out_string(&err, &buf, &blen, " EXCL");
+				if (payload & 0x10)
+					arm_spe_pkt_out_string(&err, &buf, &blen, " AR");
 			} else if (payload & 0x4) {
-				ret = snprintf(buf, buf_len, " SIMD-FP");
-				buf += ret;
-				blen -= ret;
-			}
-			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;
-			}
-			if (ret < 0)
-				return ret;
-			blen -= ret;
-			return buf_len - blen;
+				arm_spe_pkt_out_string(&err, &buf, &blen, " SIMD-FP");
 			}
-		default: return 0;
+			break;
+		case 2:
+			arm_spe_pkt_out_string(&err, &buf, &blen, "B");
+
+			if (payload & 0x1)
+				arm_spe_pkt_out_string(&err, &buf, &blen, " COND");
+			if (payload & 0x2)
+				arm_spe_pkt_out_string(&err, &buf, &blen, " IND");
+
+			break;
+		default:
+			/* Unknown index */
+			err = -1;
+			break;
 		}
+		break;
 	case ARM_SPE_DATA_SOURCE:
 	case ARM_SPE_TIMESTAMP:
-		return snprintf(buf, buf_len, "%s %lld", name, payload);
+		arm_spe_pkt_out_string(&err, &buf, &blen, "%s %lld", name, payload);
+		break;
 	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",
+			arm_spe_pkt_out_string(&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);
+			break;
+		case 2:
+			arm_spe_pkt_out_string(&err, &buf, &blen,
+					       "VA 0x%llx", payload);
+			break;
+		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;
+			arm_spe_pkt_out_string(&err, &buf, &blen,
+					       "PA 0x%llx ns=%d", payload, ns);
+			break;
+		default:
+			/* Unknown index */
+			err = -1;
+			break;
 		}
+		break;
 	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;
+		arm_spe_pkt_out_string(&err, &buf, &blen, "%s 0x%lx el%d",
+				       name, (unsigned long)payload, idx + 1);
+		break;
+	case ARM_SPE_COUNTER:
+		arm_spe_pkt_out_string(&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:
+			arm_spe_pkt_out_string(&err, &buf, &blen, "TOT");
+			break;
+		case 1:
+			arm_spe_pkt_out_string(&err, &buf, &blen, "ISSUE");
+			break;
+		case 2:
+			arm_spe_pkt_out_string(&err, &buf, &blen, "XLAT");
+			break;
+		default:
+			break;
 		}
-		if (ret < 0)
-			return ret;
-		blen -= ret;
-		return buf_len - blen;
-	}
+		break;
 	default:
+		/* Unknown packet type */
+		err = -1;
 		break;
 	}
 
-	return snprintf(buf, buf_len, "%s 0x%llx (%d)",
-			name, payload, packet->index);
+	/* Output raw data if detect any error */
+	if (err) {
+		err = 0;
+		arm_spe_pkt_out_string(&err, &buf_orig, &buf_len, "%s 0x%llx (%d)",
+				       name, payload, packet->index);
+	}
+
+	return err;
 }
diff --git a/tools/perf/util/arm-spe.c b/tools/perf/util/arm-spe.c
index 3882a5360ada..8901a1656a41 100644
--- a/tools/perf/util/arm-spe.c
+++ b/tools/perf/util/arm-spe.c
@@ -113,7 +113,7 @@ static void arm_spe_dump(struct arm_spe *spe __maybe_unused,
 		if (ret > 0) {
 			ret = arm_spe_pkt_desc(&packet, desc,
 					       ARM_SPE_PKT_DESC_MAX);
-			if (ret > 0)
+			if (!ret)
 				color_fprintf(stdout, color, " %s\n", desc);
 		} else {
 			color_fprintf(stdout, color, " Bad packet!\n");
-- 
2.17.1