Only scan global sections containing data in LSan on darwin

Summary:
__DATA segments on Darwin contain a large number of separate sections,
most of which cannot actually contain pointers, and contain const values or
objc metadata. Only scanning sections which can contain pointers greatly improves
performance.

On a medium-sized (~4000 files) internal project, I saw a speedup of about 50%
in standalone LSan's execution time (50% improvement in the time spent running
LSan, not the total program time).

Reviewers: kcc, kubamracek, alekseyshl

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D35432

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@308231 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 11 insertions, 4 deletions

diff --git a/lib/lsan/lsan_common_mac.cc b/lib/lsan/lsan_common_mac.cc
index f87c6b7e0..c0fa36fd9 100644
--- a/lib/lsan/lsan_common_mac.cc
+++ b/lib/lsan/lsan_common_mac.cc
@@ -92,8 +92,15 @@ LoadedModule *GetLinker() { return nullptr; }
 // required on Darwin.
 void InitializePlatformSpecificModules() {}
 
+// Sections which may contain global variables
+static const char *kGlobalVarSecNames[] = {
+    "__DATA",      "__bss",         "__common",       "__data",
+    "__objc_data", "__objc_opt_rw", "__objc_opt_ptrs"};
+
 // Scans global variables for heap pointers.
 void ProcessGlobalRegions(Frontier *frontier) {
+  for (auto name : kGlobalVarSecNames) CHECK(ARRAY_SIZE(name) < kMaxSegName);
+
   MemoryMappingLayout memory_mapping(false);
   InternalMmapVector<LoadedModule> modules(/*initial_capacity*/ 128);
   memory_mapping.DumpListOfModules(&modules);
@@ -104,10 +111,10 @@ void ProcessGlobalRegions(Frontier *frontier) {
 
     for (const __sanitizer::LoadedModule::AddressRange &range :
          modules[i].ranges()) {
-      // Sections storing global variables are writable and non-executable
-      if (range.executable || !range.writable) continue;
-
-      ScanGlobalRange(range.beg, range.end, frontier);
+      for (auto name : kGlobalVarSecNames) {
+        if (!internal_strcmp(range.name, name))
+          ScanGlobalRange(range.beg, range.end, frontier);
+      }
     }
   }
 }