From 8a84d383fb74135e928d341baa180c55854f2f42 Mon Sep 17 00:00:00 2001
From: Dmitriy Ivanov <dimitry@google.com>
Date: Tue, 12 Aug 2014 21:02:13 -0700
Subject: [PATCH] Optimize symbol lookup

 Do not run symbol lookup on already visited soinfos
 Not taking into account already visited libraries
 dramatically slows down dlsym in cases when there
 are multiple occurrences of a large library in
 dependency tree.

Bug: 16977077

(cherry picked from commit 042426ba6375f5c145379e598486ec6d675533c9)

Change-Id: I69d59e395e8112f119343e8a4d72fe31cd449f31
---
 linker/linked_list.h | 9 +++++++++
 linker/linker.cpp    | 8 ++++++++
 2 files changed, 17 insertions(+)

diff --git a/linker/linked_list.h b/linker/linked_list.h
index 7f8c90160..8096e623d 100644
--- a/linker/linked_list.h
+++ b/linker/linked_list.h
@@ -100,6 +100,15 @@ class LinkedList {
     }
   }
 
+  bool contains(const T* el) {
+    for (LinkedListEntry<T>* e = head_; e != nullptr; e = e->next) {
+      if (e->element != nullptr && e->element == el) {
+        return true;
+      }
+    }
+    return false;
+  }
+
  private:
   LinkedListEntry<T>* head_;
   LinkedListEntry<T>* tail_;
diff --git a/linker/linker.cpp b/linker/linker.cpp
index f8b35d7a8..77fb70c29 100644
--- a/linker/linker.cpp
+++ b/linker/linker.cpp
@@ -607,17 +607,24 @@ class SoinfoListAllocatorRW {
 // specified soinfo object and its dependencies in breadth first order.
 ElfW(Sym)* dlsym_handle_lookup(soinfo* si, soinfo** found, const char* name, soinfo* caller) {
   LinkedList<soinfo, SoinfoListAllocatorRW> visit_list;
+  LinkedList<soinfo, SoinfoListAllocatorRW> visited;
   visit_list.push_back(si);
   soinfo* current_soinfo;
   while ((current_soinfo = visit_list.pop_front()) != nullptr) {
+    if (visited.contains(current_soinfo)) {
+      continue;
+    }
+
     ElfW(Sym)* result = soinfo_elf_lookup(current_soinfo, elfhash(name), name,
         caller == current_soinfo ? SymbolLookupScope::kAllowLocal : SymbolLookupScope::kExcludeLocal);
 
     if (result != nullptr) {
       *found = current_soinfo;
       visit_list.clear();
+      visited.clear();
       return result;
     }
+    visited.push_back(current_soinfo);
 
     current_soinfo->get_children().for_each([&](soinfo* child) {
       visit_list.push_back(child);
@@ -625,6 +632,7 @@ ElfW(Sym)* dlsym_handle_lookup(soinfo* si, soinfo** found, const char* name, soi
   }
 
   visit_list.clear();
+  visited.clear();
   return nullptr;
 }