Added --debug-syms-by-id option

bin/jeprof.in

@@ -240,6 +240,7 @@ Miscellaneous:
    --test              Run unit tests
    --help              This message
    --version           Version information
+   --debug-syms-by-id  (Linux only) Find debug symbol files by build ID as well as by name
 
 Environment Variables:
    JEPROF_TMPDIR        Profiles directory. Defaults to \$HOME/jeprof
@@ -365,6 +366,7 @@ sub Init() {
   $main::opt_tools   = "";
   $main::opt_debug   = 0;
   $main::opt_test    = 0;
+  $main::opt_debug_syms_by_id = 0;
 
   # These are undocumented flags used only by unittests.
   $main::opt_test_stride = 0;
@@ -433,6 +435,7 @@ sub Init() {
              "tools=s"        => \$main::opt_tools,
              "test!"          => \$main::opt_test,
              "debug!"         => \$main::opt_debug,
+             "debug-syms-by-id!" => \$main::opt_debug_syms_by_id,
              # Undocumented flags used only by unittests:
              "test_stride=i"  => \$main::opt_test_stride,
       ) || usage("Invalid option(s)");
@@ -577,6 +580,11 @@ sub Init() {
   foreach (@prefix_list) {
     s|/+$||;
   }
+
+  # Flag to prevent us from trying over and over to use
+  #  elfutils if it's not installed (used only with
+  #  --debug-syms-by-id option).
+  $main::gave_up_on_elfutils = 0;
 }
 
 sub FilterAndPrint {
@@ -4492,16 +4500,54 @@ sub FindLibrary {
 # For libc libraries, the copy in /usr/lib/debug contains debugging symbols
 sub DebuggingLibrary {
   my $file = shift;
-  if ($file =~ m|^/|) {
+      
-      if (-f "/usr/lib/debug$file") {
+  if ($file !~ m|^/|) {
-        return "/usr/lib/debug$file";
-      } elsif (-f "/usr/lib/debug$file.debug") {
-        return "/usr/lib/debug$file.debug";
-      }
-  }
     return undef;
   }
       
+  # Find debug symbol file if it's named after the library's name.
+  
+  if (-f "/usr/lib/debug$file") {                 
+    if($main::opt_debug) { print STDERR "found debug info for $file in /usr/lib/debug$file\n"; }
+    return "/usr/lib/debug$file";
+  } elsif (-f "/usr/lib/debug$file.debug") {
+    if($main::opt_debug) { print STDERR "found debug info for $file in /usr/lib/debug$file.debug\n"; }
+    return "/usr/lib/debug$file.debug"; 
+  }
+
+  if(!$main::opt_debug_syms_by_id) {
+    if($main::opt_debug) { print STDERR "no debug symbols found for $file\n" };
+    return undef;
+  }
+
+  # Find debug file if it's named after the library's build ID.
+  
+  my $readelf = '';
+  if (!$main::gave_up_on_elfutils) {
+    $readelf = qx/eu-readelf -n ${file}/;
+    if ($?) {
+      print STDERR "Cannot run eu-readelf. To use --debug-syms-by-id you must be on Linux, with elfutils installed.\n";
+      $main::gave_up_on_elfutils = 1;
+      return undef;
+    }
+    my $buildID = $1 if $readelf =~ /Build ID: ([A-Fa-f0-9]+)/s;
+    if (defined $buildID && length $buildID > 0) {
+      my $symbolFile = '/usr/lib/debug/.build-id/' . substr($buildID, 0, 2) . '/' . substr($buildID, 2) . '.debug';
+      if (-e $symbolFile) {
+        if($main::opt_debug) { print STDERR "found debug symbol file $symbolFile for $file\n" };
+        return $symbolFile;
+      } else {
+        if($main::opt_debug) { print STDERR "no debug symbol file found for $file, build ID: $buildID\n" };
+        return undef;
+      }
+    }
+  }
+
+  if($main::opt_debug) { print STDERR "no debug symbols found for $file, build ID unknown\n" };
+  return undef;
+}
+
+
 # Parse text section header of a library using objdump
 sub ParseTextSectionHeaderFromObjdump {
   my $lib = shift;