issue-654: [pprof] handle split text segments

This applies patch by user simonb.

Quoting:

Relocation packing splits a single executable load segment into two.  Before:

  LOAD           0x000000 0x00000000 0x00000000 0x2034d28 0x2034d28 R E 0x1000
  LOAD           0x2035888 0x02036888 0x02036888 0x182d38 0x1a67d0 RW  0x1000

After:
  LOAD           0x000000 0x00000000 0x00000000 0x14648 0x14648 R E 0x1000
  LOAD           0x014648 0x0020c648 0x0020c648 0x1e286e0 0x1e286e0 R E 0x1000
  ...
  LOAD           0x1e3d888 0x02036888 0x02036888 0x182d38 0x1a67d0 RW  0x1000

The .text section is in the second LOAD, and this is not at
offset/address zero.  The result is that this library shows up in
/proc/self/maps as multiple executable entries, for example (note:
this trace is not from the library dissected above, but rather from an
earlier version of it):

  73b0c000-73b21000 r-xp 00000000 b3:19 786460 /data/.../libchrome.2160.0.so
  73b21000-73d12000 ---p 00000000 00:00 0
  73d12000-75a90000 r-xp 00014000 b3:19 786460 /data/.../libchrome.2160.0.so
  75a90000-75c0d000 rw-p 01d91000 b3:19 786460 /data/.../libchrome.2160.0.so

When parsing this, pprof needs to merge the two r-xp entries above
into a single entry, otherwise the addresses it prints are incorrect.

The following fix against 2.2.1 was sufficient to make pprof --text
print the correct output.  Untested with other pprof options.

1 files changed, 10 insertions, 0 deletions

diff --git a/src/pprof b/src/pprof
index 0135fed..719e859 100755
--- a/src/pprof
+++ b/src/pprof
@@ -4395,6 +4395,7 @@ sub ParseLibraries {
   my $zero_offset = HexExtend("0");
 
   my $buildvar = "";
+  my $priorlib = "";
   foreach my $l (split("\n", $map)) {
     if ($l =~ m/^\s*build=(.*)$/) {
       $buildvar = $1;
@@ -4451,7 +4452,16 @@ sub ParseLibraries {
       }
     }
 
+    # If we find multiple executable segments for a single library, merge them
+    # into a single entry that spans the complete address range.
+    if ($lib eq $priorlib) {
+      my $prior = pop(@{$result});
+      $start = @$prior[1];
+      # TODO $offset may be wrong if .text is not in the final segment.
+    }
+
     push(@{$result}, [$lib, $start, $finish, $offset]);
+    $priorlib = $lib;
   }
 
   # Append special entry for additional library (not relocated)