Handle memory maps generated by logging

If the memory map is generated by logging routines such as glog, they
may include some initial text which confuses the parsing of legacy
mappings. The initial text is the same for all mapping entries,
so detect it on the proc map sentinel and remove it from the mapping
entries.

profile/legacy_profile.go

@@ -509,7 +509,7 @@ func parseHeap(b []byte) (p *Profile, err error) {
 			continue
 		}
 
-		if sectionTrigger(line) != unrecognizedSection {
+		if isMemoryMapSentinel(line) {
 			break
 		}
 
@@ -837,7 +837,7 @@ func parseThread(b []byte) (*Profile, error) {
 	if m := threadzStartRE.FindStringSubmatch(line); m != nil {
 		// Advance over initial comments until first stack trace.
 		for s.Scan() {
-			if line = s.Text(); sectionTrigger(line) != unrecognizedSection || strings.HasPrefix(line, "-") {
+			if line = s.Text(); isMemoryMapSentinel(line) || strings.HasPrefix(line, "-") {
 				break
 			}
 		}
@@ -853,7 +853,7 @@ func parseThread(b []byte) (*Profile, error) {
 
 	locs := make(map[uint64]*Location)
 	// Recognize each thread and populate profile samples.
-	for sectionTrigger(line) == unrecognizedSection {
+	for !isMemoryMapSentinel(line) {
 		if strings.HasPrefix(line, "---- no stack trace for") {
 			line = ""
 			break
@@ -944,12 +944,12 @@ func parseThreadSample(s *bufio.Scanner) (nextl string, addrs []uint64, err erro
 // parseAdditionalSections parses any additional sections in the
 // profile, ignoring any unrecognized sections.
 func parseAdditionalSections(s *bufio.Scanner, p *Profile) error {
-	for sectionTrigger(s.Text()) != memoryMapSection && s.Scan() {
+	for !isMemoryMapSentinel(s.Text()) && s.Scan() {
 	}
 	if err := s.Err(); err != nil {
 		return err
 	}
-	return p.parseMemoryMapFromScanner(s)
+	return p.ParseMemoryMapFromScanner(s)
 }
 
 // ParseProcMaps parses a memory map in the format of /proc/self/maps.
@@ -964,12 +964,19 @@ func ParseProcMaps(rd io.Reader) ([]*Mapping, error) {
 func parseProcMapsFromScanner(s *bufio.Scanner) ([]*Mapping, error) {
 	var mapping []*Mapping
 
+	// If the memory-map sentinel is at column X, assume memory mappings
+	// also start at X. This is useful to eliminate logging information.
+	offset := memoryMapSentinelOffset(s.Text())
+
 	var attrs []string
 	var r *strings.Replacer
 	const delimiter = "="
 	for s.Scan() {
-		line := strings.TrimSpace(s.Text())
-		if line == "" {
+		line := s.Text()
+		if len(line) > offset {
+			line = line[offset:]
+		}
+		if line = strings.TrimSpace(line); line == "" {
 			continue
 		}
 
@@ -1005,10 +1012,10 @@ func parseProcMapsFromScanner(s *bufio.Scanner) ([]*Mapping, error) {
 // /proc/self/maps, and overrides the mappings in the current profile.
 // It renumbers the samples and locations in the profile correspondingly.
 func (p *Profile) ParseMemoryMap(rd io.Reader) error {
-	return p.parseMemoryMapFromScanner(bufio.NewScanner(rd))
+	return p.ParseMemoryMapFromScanner(bufio.NewScanner(rd))
 }
 
-func (p *Profile) parseMemoryMapFromScanner(s *bufio.Scanner) error {
+func (p *Profile) ParseMemoryMapFromScanner(s *bufio.Scanner) error {
 	mapping, err := parseProcMapsFromScanner(s)
 	if err != nil {
 		return err
@@ -1054,25 +1061,32 @@ func parseMappingEntry(l string) (*Mapping, error) {
 	return mapping, nil
 }
 
-type sectionType int
-
-const (
-	unrecognizedSection sectionType = iota
-	memoryMapSection
-)
-
-var memoryMapTriggers = []string{
+var memoryMapSentinels = []string{
 	"--- Memory map: ---",
 	"MAPPED_LIBRARIES:",
 }
 
-func sectionTrigger(line string) sectionType {
-	for _, trigger := range memoryMapTriggers {
-		if strings.Contains(line, trigger) {
-			return memoryMapSection
+// isMemoryMapSentinel returns true if the string contains one of the
+// known sentinels for memory map information.
+func isMemoryMapSentinel(line string) bool {
+	for _, s := range memoryMapSentinels {
+		if strings.Contains(line, s) {
+			return true
+		}
+	}
+	return false
+}
+
+// memoryMapSentinelOffset returns the index of a known memory map
+// sentinel in the string. If the string does not contain a sentinel,
+// it returns 0.
+func memoryMapSentinelOffset(line string) int {
+	for _, s := range memoryMapSentinels {
+		if i := strings.Index(line, s); i != -1 {
+			return i
 		}
 	}
-	return unrecognizedSection
+	return 0
 }
 
 func (p *Profile) addLegacyFrameInfo() {