Add shared symbol name cache.

The symbol name related reads and memory operations
take about half of the symbol name reading cost now.

This CL adds ref-counted read-only shared string cache,
which essentially eliminates all of the costs.

BM_symbol_find_single_many_times is >10% faster on ARM.
(which is 20% if we exclude the fixed ELF loading cost)
Real-world profiles seem even more encouraging.

The extra memory cost is negligible (by definition,
a small fraction of the decompressed mini-debug-info:
specifically, the subset of strtab for hit functions).

Furthermore, this effectively dedups strings when
consecutive unwinds hit similar set of functions.
(perfetto might keep several unwind results live)

Test: m libunwindstack_unit_test
Change-Id: I5cf600bb972fdb9d0f3a57ed0997bead2efa38f4

1 files changed, 6 insertions, 4 deletions

diff --git a/libunwindstack/Symbols.h b/libunwindstack/Symbols.h
index 97c03c2..1074ebf 100644
--- a/libunwindstack/Symbols.h
+++ b/libunwindstack/Symbols.h
@@ -23,6 +23,8 @@
 #include <optional>
 #include <string>
 
+#include <unwindstack/SharedString.h>
+
 namespace unwindstack {
 
 // Forward declaration.
@@ -30,9 +32,9 @@ class Memory;
 
 class Symbols {
   struct Info {
-    uint64_t addr;   // Symbol address.
+    uint32_t size;   // Symbol size in bytes.
     uint32_t index;  // Index into *sorted* symbol table.
-    uint32_t name;   // Offset in .strtab, or 0 if the symbol is not a function.
+    SharedString name;
   };
 
  public:
@@ -41,7 +43,7 @@ class Symbols {
   virtual ~Symbols() = default;
 
   template <typename SymType>
-  bool GetName(uint64_t addr, Memory* elf_memory, std::string* name, uint64_t* func_offset);
+  bool GetName(uint64_t addr, Memory* elf_memory, SharedString* name, uint64_t* func_offset);
 
   template <typename SymType>
   bool GetGlobal(Memory* elf_memory, const std::string& name, uint64_t* memory_address);
@@ -53,7 +55,7 @@ class Symbols {
 
  private:
   template <typename SymType, bool RemapIndices>
-  const Info* BinarySearch(uint64_t addr, Memory* elf_memory);
+  Info* BinarySearch(uint64_t addr, Memory* elf_memory, uint64_t* func_offset);
 
   template <typename SymType>
   void BuildRemapTable(Memory* elf_memory);