Update logic for emitting region information from dyld.

components/tracing/common/process_metrics_memory_dump_provider.cc

Index: components/tracing/common/process_metrics_memory_dump_provider.cc
diff --git a/components/tracing/common/process_metrics_memory_dump_provider.cc b/components/tracing/common/process_metrics_memory_dump_provider.cc
index ccac246654069fb66a624e55b5816d28de403ec9..1406689fcac30de729d6407381b459228fa72b6a 100644
--- a/components/tracing/common/process_metrics_memory_dump_provider.cc
+++ b/components/tracing/common/process_metrics_memory_dump_provider.cc
@@ -271,7 +271,8 @@ bool GetDyldRegions(std::vector<VMRegion>* regions) {
 
     uint64_t next_command = reinterpret_cast<uint64_t>(header + 1);
     uint64_t command_end = next_command + header->sizeofcmds;
-    for (unsigned int i = 0; i < header->ncmds; ++i) {
+    uint64_t slide = 0;
+    for (unsigned int j = 0; j < header->ncmds; ++j) {
       // Ensure that next_command doesn't run past header->sizeofcmds.
       if (next_command + sizeof(struct load_command) > command_end)
         return false;
@@ -286,6 +287,16 @@ bool GetDyldRegions(std::vector<VMRegion>* regions) {
             reinterpret_cast<const segment_command_64*>(load_cmd);
         if (strcmp(seg->segname, SEG_PAGEZERO) == 0)
           continue;
+        if (strcmp(seg->segname, SEG_TEXT) == 0) {
+          slide = reinterpret_cast<uint64_t>(header) - seg->vmaddr;
+        }
+
+        // Avoid emitting LINKEDIT regions in the dyld shared cache, since they

[Mark Mentovai, 2017/02/14 22:18:58]

Perhaps just emit it one time, then? Show it as belonging to the shared cache
instead of any particular module?

[erikchen, 2017/02/14 22:33:47]

Done.

+        // all overlap.
+        if (IsAddressInSharedRegion(seg->vmaddr) &&
+            strcmp(seg->segname, SEG_LINKEDIT) == 0) {
+          continue;
+        }
 
         uint32_t protection_flags = 0;
         if (seg->initprot & VM_PROT_READ)
@@ -299,8 +310,7 @@ bool GetDyldRegions(std::vector<VMRegion>* regions) {
         region.size_in_bytes = seg->vmsize;
         region.protection_flags = protection_flags;
         region.mapped_file = image_name;
-        region.start_address =
-            reinterpret_cast<uint64_t>(header) + seg->fileoff;
+        region.start_address = slide + seg->vmaddr;
 
         // We intentionally avoid setting any page information, which is not
         // available from dyld. The fields will be populated later.
@@ -429,10 +439,7 @@ bool ProcessMetricsMemoryDumpProvider::DumpProcessMemoryMaps(
   // Cache information from dyld_regions in a data-structure more conducive to
   // fast lookups.
   std::unordered_map<uint64_t, VMRegion*> address_to_vm_region;
-  std::vector<uint64_t> addresses_in_shared_region;
   for (VMRegion& region : dyld_regions) {
-    if (IsAddressInSharedRegion(region.start_address))
-      addresses_in_shared_region.push_back(region.start_address);
     address_to_vm_region[region.start_address] = &region;
   }
 
@@ -450,17 +457,29 @@ bool ProcessMetricsMemoryDumpProvider::DumpProcessMemoryMaps(
     // Check to see if the region is likely used for the dyld shared cache.
     if (IsAddressInSharedRegion(region.start_address)) {
       uint64_t end_address = region.start_address + region.size_in_bytes;
-      for (uint64_t address : addresses_in_shared_region) {
+      bool skip = false;
+      for (const VMRegion& dyld_region : dyld_regions) {
         // This region is likely used for the dyld shared cache. Don't record
         // any byte stats since:
         //   1. It's not possible to figure out which dyld regions the byte
         //      stats correspond to.
         //   2. The region is likely shared by non-Chrome processes, so there's
         //      no point in charging the pages towards Chrome.
-        if (address >= region.start_address && address < end_address) {
-          continue;
+        if (dyld_region.start_address >= region.start_address &&
+            dyld_region.start_address < end_address) {
+          skip = true;
+          break;
+        }
+        uint64_t dyld_end_address =
+            dyld_region.start_address + dyld_region.size_in_bytes;
+        if (dyld_end_address >= region.start_address &&
+            dyld_end_address < end_address) {
+          skip = true;
+          break;
         }
       }
+      if (skip)
+        continue;
     }
     pmd->process_mmaps()->AddVMRegion(region);
   }