pkg/symbolizer: retain the frame if line number is 0

There are numerous line_entries with a line number of 0 for
__sanitizer_cov_trace_pc.
Currently, if only one program counter (PC) is hit in the function and
the line number is 0 for that PC, the frame is ignored.
To accurately report function coverage, we should include the function
in such cases.

Author: jiangenj

pkg/symbolizer/addr2line.go

@@ -163,9 +163,12 @@ func parse(interner *Interner, s *bufio.Scanner) ([]Frame, error) {
 		}
 		file := ln[:colon]
 		line, err := strconv.Atoi(ln[colon+1 : lineEnd])
-		if err != nil || fn == "" || fn == "??" || file == "" || file == "??" || line <= 0 {
+		if err != nil || fn == "" || fn == "??" || file == "" || file == "??" || line < 0 {
 			continue
 		}
+		if line == 0 {
+			line = -1
+		}
 		frames = append(frames, Frame{
 			PC:     pc,
 			Func:   interner.Do(fn),

pkg/symbolizer/addr2line_test.go

@@ -72,6 +72,21 @@ func TestParse(t *testing.T) {
 				},
 			},
 		},
+		{
+			0xffffffff82fdbe1b,
+			"0xffffffff82fdbe1b\n" +
+				"fbcon_invert_region\n" +
+				"drivers/video/console/fbcon.c:0\n",
+			[]Frame{
+				{
+					PC:     0xffffffff82fdbe1b,
+					Func:   "fbcon_invert_region",
+					File:   "drivers/video/console/fbcon.c",
+					Line:   -1,
+					Inline: false,
+				},
+			},
+		},
 		{
 			0x123124,
 			"0x0000000000123124\n" +