Fix which maps to search for globals.

If multiple threads are unwinding at the same time, new maps that contain
the global variables for dex files and jit information are created. This
leads to threads creating more new maps that then get searched, then
more maps, then more searching until virtual address space exhaustion.

Fix this so that we only search maps that have a corresponding rw map that
could contain the global memory.

Small refactor to combine the code to search for global variables into
one class that both classes inherit from.

Modify unit tests for the new pattern checking.

Bug: 117761427

Test: Ran unit tests for libunwindstack/libbacktrace/simpleperf.
Test: Ran art 004-ThreadStress that used to fail.
Change-Id: I837ca6b9d0383100079de090bc7d019598e0cdfe

1 files changed, 8 insertions, 32 deletions

diff --git a/libunwindstack/DexFiles.cpp b/libunwindstack/DexFiles.cpp
index 17e252699..ac55fee99 100644
--- a/libunwindstack/DexFiles.cpp
+++ b/libunwindstack/DexFiles.cpp
@@ -43,10 +43,10 @@ struct DEXFileEntry64 {
   uint64_t dex_file;
 };
 
-DexFiles::DexFiles(std::shared_ptr<Memory>& memory) : memory_(memory) {}
+DexFiles::DexFiles(std::shared_ptr<Memory>& memory) : Global(memory) {}
 
 DexFiles::DexFiles(std::shared_ptr<Memory>& memory, std::vector<std::string>& search_libs)
-    : memory_(memory), search_libs_(search_libs) {}
+    : Global(memory, search_libs) {}
 
 DexFiles::~DexFiles() {
   for (auto& entry : files_) {
@@ -117,6 +117,11 @@ bool DexFiles::ReadEntry64() {
   return true;
 }
 
+bool DexFiles::ReadVariableData(uint64_t ptr_offset) {
+  entry_addr_ = (this->*read_entry_ptr_func_)(ptr_offset);
+  return entry_addr_ != 0;
+}
+
 void DexFiles::Init(Maps* maps) {
   if (initialized_) {
     return;
@@ -124,36 +129,7 @@ void DexFiles::Init(Maps* maps) {
   initialized_ = true;
   entry_addr_ = 0;
 
-  const std::string dex_debug_name("__dex_debug_descriptor");
-  for (MapInfo* info : *maps) {
-    if (!(info->flags & PROT_READ) || info->offset != 0) {
-      continue;
-    }
-
-    if (!search_libs_.empty()) {
-      bool found = false;
-      const char* lib = basename(info->name.c_str());
-      for (const std::string& name : search_libs_) {
-        if (name == lib) {
-          found = true;
-          break;
-        }
-      }
-      if (!found) {
-        continue;
-      }
-    }
-
-    Elf* elf = info->GetElf(memory_, true);
-    uint64_t ptr;
-    // Find first non-empty list (libart might be loaded multiple times).
-    if (elf->GetGlobalVariable(dex_debug_name, &ptr) && ptr != 0) {
-      entry_addr_ = (this->*read_entry_ptr_func_)(ptr + info->start);
-      if (entry_addr_ != 0) {
-        break;
-      }
-    }
-  }
+  FindAndReadVariable(maps, "__dex_debug_descriptor");
 }
 
 DexFile* DexFiles::GetDexFile(uint64_t dex_file_offset, MapInfo* info) {