perf tests: objdump output can contain multi byte chunks

objdump's raw insn output can vary across architectures on number of
bytes per chunk (bpc) displayed and their endian.

code-reading test relied on reading objdump output as 1 bpc. Kaixu Xia
reported test failure on ARM64, where objdump displays 4 bpc:
  70c48:        f90027bf         str        xzr, [x29,torvalds#72]
  70c4c:        91224000         add        x0, x0, #0x890
  70c50:        f90023a0         str        x0, [x29,torvalds#64]

This patch adds support to read raw insn output for any bpc length.
In case of 2+ bpc it also guesses objdump's display endian.

Signed-off-by: Jan Stancek <[email protected]>
Reported-and-tested-by: Kaixu Xia <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Corey Ashford <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Peter Zijlstra <[email protected]>

tools/perf/tests/code-reading.c

@@ -33,44 +33,86 @@ static unsigned int hex(char c)
 	return c - 'A' + 10;
 }
 
-static size_t read_objdump_line(const char *line, size_t line_len, void *buf,
-			      size_t len)
+static size_t read_objdump_chunk(const char **line, unsigned char **buf,
+				 size_t *buf_len)
 {
-	const char *p;
-	size_t i, j = 0;
-
-	/* Skip to a colon */
-	p = strchr(line, ':');
-	if (!p)
-		return 0;
-	i = p + 1 - line;
+	size_t bytes_read = 0;
+	unsigned char *chunk_start = *buf;
 
 	/* Read bytes */
-	while (j < len) {
+	while (*buf_len > 0) {
 		char c1, c2;
 
-		/* Skip spaces */
-		for (; i < line_len; i++) {
-			if (!isspace(line[i]))
-				break;
-		}
 		/* Get 2 hex digits */
-		if (i >= line_len || !isxdigit(line[i]))
+		c1 = *(*line)++;
+		if (!isxdigit(c1))
 			break;
-		c1 = line[i++];
-		if (i >= line_len || !isxdigit(line[i]))
+		c2 = *(*line)++;
+		if (!isxdigit(c2))
 			break;
-		c2 = line[i++];
-		/* Followed by a space */
-		if (i < line_len && line[i] && !isspace(line[i]))
+
+		/* Store byte and advance buf */
+		**buf = (hex(c1) << 4) | hex(c2);
+		(*buf)++;
+		(*buf_len)--;
+		bytes_read++;
+
+		/* End of chunk? */
+		if (isspace(**line))
 			break;
-		/* Store byte */
-		*(unsigned char *)buf = (hex(c1) << 4) | hex(c2);
-		buf += 1;
-		j++;
 	}
+
+	/*
+	 * objdump will display raw insn as LE if code endian
+	 * is LE and bytes_per_chunk > 1. In that case reverse
+	 * the chunk we just read.
+	 *
+	 * see disassemble_bytes() at binutils/objdump.c for details
+	 * how objdump chooses display endian)
+	 */
+	if (bytes_read > 1 && !bigendian()) {
+		unsigned char *chunk_end = chunk_start + bytes_read - 1;
+		unsigned char tmp;
+
+		while (chunk_start < chunk_end) {
+			tmp = *chunk_start;
+			*chunk_start = *chunk_end;
+			*chunk_end = tmp;
+			chunk_start++;
+			chunk_end--;
+		}
+	}
+
+	return bytes_read;
+}
+
+static size_t read_objdump_line(const char *line, unsigned char *buf,
+				size_t buf_len)
+{
+	const char *p;
+	size_t ret, bytes_read = 0;
+
+	/* Skip to a colon */
+	p = strchr(line, ':');
+	if (!p)
+		return 0;
+	p++;
+
+	/* Skip initial spaces */
+	while (*p) {
+		if (!isspace(*p))
+			break;
+		p++;
+	}
+
+	do {
+		ret = read_objdump_chunk(&p, &buf, &buf_len);
+		bytes_read += ret;
+		p++;
+	} while (ret > 0);
+
 	/* return number of successfully read bytes */
-	return j;
+	return bytes_read;
 }
 
 static int read_objdump_output(FILE *f, void *buf, size_t *len, u64 start_addr)
@@ -95,7 +137,7 @@ static int read_objdump_output(FILE *f, void *buf, size_t *len, u64 start_addr)
 		}
 
 		/* read objdump data into temporary buffer */
-		read_bytes = read_objdump_line(line, ret, tmp, sizeof(tmp));
+		read_bytes = read_objdump_line(line, tmp, sizeof(tmp));
 		if (!read_bytes)
 			continue;
 
@@ -152,7 +194,7 @@ static int read_via_objdump(const char *filename, u64 addr, void *buf,
 
 	ret = read_objdump_output(f, buf, &len, addr);
 	if (len) {
-		pr_debug("objdump read too few bytes\n");
+		pr_debug("objdump read too few bytes: %lu\n", len);
 		if (!ret)
 			ret = len;
 	}