[PATCH v1 2/2] perf srcline: Make sentinel reading for binutils addr2line more robust

[Ian Rogers <irogers@google.com>]

The addr2line process is sent an address then multiple function,
filename:line "records" are read. To detect the end of output a ',' is
sent and for llvm-addr2line a ',' is then read back showing the end of
addrline's output. For binutils addr2line the ',' translates to
address 0 and we expect the bogus filename marker "??:0" (see
filename_split) to be sent from addr2line. For some kernels address 0
may have a mapping and so a seemingly valid inline output is given and
breaking the sentinel discovery:

```
$ addr2line -e vmlinux -f -i
,
__per_cpu_start
./arch/x86/kernel/cpu/common.c:1850
```

To avoid this problem enable the address dumping for addr2line (the -a
option). If an address of 0x0000000000000000 is read then this is the
sentinel value working around the problem above. The filename_split
still needs to check for "??:0" as bogus non-zero addresses also need
handling.

Reported-by: Changbin Du <changbin.du@huawei.com>
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/srcline.c | 61 ++++++++++++++++++++++++++++++++++-----
 1 file changed, 53 insertions(+), 8 deletions(-)

diff --git a/tools/perf/util/srcline.c b/tools/perf/util/srcline.c
index fc85cdd6c8f9..c99a001453b4 100644
--- a/tools/perf/util/srcline.c
+++ b/tools/perf/util/srcline.c
@@ -406,7 +406,7 @@ static struct child_process *addr2line_subprocess_init(const char *addr2line_pat
 	const char *argv[] = {
 		addr2line_path ?: "addr2line",
 		"-e", binary_path,
-		"-i", "-f", NULL
+		"-a", "-i", "-f", NULL
 	};
 	struct child_process *a2l = zalloc(sizeof(*a2l));
 	int start_command_status = 0;
@@ -461,10 +461,10 @@ static enum a2l_style addr2line_configure(struct child_process *a2l, const char
 			style = LLVM;
 			cached = true;
 			lines = 1;
-		} else if (ch == '?') {
+		} else if (ch == '0') {
 			style = GNU_BINUTILS;
 			cached = true;
-			lines = 2;
+			lines = 3;
 		} else {
 			if (!symbol_conf.disable_add2line_warn) {
 				char *output;
@@ -516,20 +516,64 @@ static int read_addr2line_record(struct io *io,
 	if (line_nr != NULL)
 		*line_nr = 0;
 
+	/*
+	 * Read the first line. Without an error this will be either an address
+	 * like 0x1234 or for llvm-addr2line the sentinal ',' character.
+	 */
 	if (io__getline(io, &line, &line_len) < 0 || !line_len)
 		goto error;
 
-	if (style == LLVM && line_len == 2 && line[0] == ',') {
-		zfree(&line);
-		return 0;
+	if (style == LLVM) {
+		if (line_len == 2 && line[0] == ',') {
+			zfree(&line);
+			return 0;
+		}
+	} else {
+		int zero_count = 0, non_zero_count = 0;
+
+		/* The address should always start 0x. */
+		if (line_len < 2 || line[0] != '0' || line[1] != 'x')
+			goto error;
+
+		for (size_t i = 2; i < line_len; i++) {
+			if (line[i] == '0')
+				zero_count++;
+			else
+				non_zero_count++;
+		}
+		if (!non_zero_count) {
+			int ch;
+
+			if (!zero_count) {
+				/* Line was erroneous just '0x'. */
+				goto error;
+			}
+			/*
+			 * Line was 0x0..0, the sentinel for binutils. Remove
+			 * the function and filename lines.
+			 */
+			zfree(&line);
+			do {
+				ch = io__get_char(io);
+			} while (ch > 0 && ch != '\n');
+			do {
+				ch = io__get_char(io);
+			} while (ch > 0 && ch != '\n');
+			return 0;
+		}
 	}
 
+	/* Read the second function name line. */
+	if (io__getline(io, &line, &line_len) < 0 || !line_len)
+		goto error;
+
 	if (function != NULL)
 		*function = strdup(strim(line));
 
 	zfree(&line);
 	line_len = 0;
 
+	/* Read the third filename and line number line. */
 	if (io__getline(io, &line, &line_len) < 0 || !line_len)
 		goto error;
 
@@ -633,8 +677,9 @@ static int addr2line(const char *dso_name, u64 addr,
 		goto out;
 	case 0:
 		/*
-		 * The first record was invalid, so return failure, but first read another
-		 * record, since we asked a junk question and have to clear the answer out.
+		 * The first record was invalid, so return failure, but first
+		 * read another record, since we sent a sentinel ',' for the
+		 * sake of detected the last inlined function.
 		 */
 		switch (read_addr2line_record(&io, a2l_style, NULL, NULL, NULL)) {
 		case -1:
-- 
2.41.0.162.gfafddb0af9-goog