Add a string pool to store functions names

- Added StringView which is used as a reference to a string, but
doesn't own the string.
- Removed the old string pool in DwarfCUToModule::FilePrivate, since
it's doing string copy.
- Added a string pool in Module to store functions/inline origins'
names (mangled and demangled).
- The peak memory usage drops from 20.6 GB to 12.5 GB when disabling
inline records and drops from 36 GB to 20.3 GB when enabling inline records.

Bug: chromium:1246974, chromium:1250351
Change-Id: Ie7e9740ea10c1930a0fc58c6becaae2d718b83b8
Reviewed-on: https://chromium-review.googlesource.com/c/breakpad/breakpad/+/3189410
Reviewed-by: Joshua Peraza <jperaza@chromium.org>

src/common/dwarf_cu_to_module.cc

@@ -48,8 +48,8 @@
 #include <numeric>
 #include <utility>
 
+#include "common/string_view.h"
 #include "common/dwarf_line_to_module.h"
-#include "common/unordered.h"
 #include "google_breakpad/common/breakpad_types.h"
 
 namespace google_breakpad {
@@ -80,22 +80,21 @@ using std::unique_ptr;
 // we may need if we find a DW_AT_specification link pointing to it.
 struct DwarfCUToModule::Specification {
   // The qualified name that can be found by demangling DW_AT_MIPS_linkage_name.
-  string qualified_name;
+  StringView qualified_name;
 
   // The name of the enclosing scope, or the empty string if there is none.
-  string enclosing_name;
+  StringView enclosing_name;
 
   // The name for the specification DIE itself, without any enclosing
   // name components.
-  string unqualified_name;
+  StringView unqualified_name;
 };
 
 // An abstract origin -- base definition of an inline function.
 struct AbstractOrigin {
-  AbstractOrigin() : name() {}
-  explicit AbstractOrigin(const string& name) : name(name) {}
+  explicit AbstractOrigin(StringView name) : name(name) {}
 
-  string name;
+  StringView name;
 };
 
 typedef map<uint64_t, AbstractOrigin> AbstractOriginByOffset;
@@ -103,25 +102,6 @@ typedef map<uint64_t, AbstractOrigin> AbstractOriginByOffset;
 // Data global to the DWARF-bearing file that is private to the
 // DWARF-to-Module process.
 struct DwarfCUToModule::FilePrivate {
-  // A set of strings used in this CU. Before storing a string in one of
-  // our data structures, insert it into this set, and then use the string
-  // from the set.
-  //
-  // In some STL implementations, strings are reference-counted internally,
-  // meaning that simply using strings from this set, even if passed by
-  // value, assigned, or held directly in structures and containers
-  // (map<string, ...>, for example), causes those strings to share a
-  // single instance of each distinct piece of text. GNU's libstdc++ uses
-  // reference counts, and I believe MSVC did as well, at some point.
-  // However, C++ '11 implementations are moving away from reference
-  // counting.
-  //
-  // In other implementations, string assignments copy the string's text,
-  // so this set will actually hold yet another copy of the string (although
-  // everything will still work). To improve memory consumption portably,
-  // we will probably need to use pointers to strings held in this set.
-  unordered_set<string> common_strings;
-
   // A map from offsets of DIEs within the .debug_info section to
   // Specifications describing those DIEs. Specification references can
   // cross compilation unit boundaries.
@@ -293,7 +273,7 @@ struct DwarfCUToModule::DIEContext {
   // in a C++ compilation unit, the DIEContext's name for the
   // DW_TAG_subprogram DIE would be "Foo::Bar". The DIEContext's
   // name for the DW_TAG_namespace DIE would be "".
-  string name;
+  StringView name;
 };
 
 // An abstract base class for all the dumper's DIE handlers.
@@ -339,20 +319,12 @@ class DwarfCUToModule::GenericDIEHandler: public DIEHandler {
   // Use this from EndAttributes member functions, not ProcessAttribute*
   // functions; only the former can be sure that all the DIE's attributes
   // have been seen.
-  string ComputeQualifiedName();
+  StringView ComputeQualifiedName();
 
   CUContext* cu_context_;
   DIEContext* parent_context_;
   uint64_t offset_;
 
-  // Place the name in the global set of strings. Even though this looks
-  // like a copy, all the major string implementations use reference
-  // counting internally, so the effect is to have all the data structures
-  // share copies of strings whenever possible.
-  // FIXME: Should this return something like a string_ref to avoid the
-  // assumption about how strings are implemented?
-  string AddStringToPool(const string& str);
-
   // If this DIE has a DW_AT_declaration attribute, this is its value.
   // It is false on DIEs with no DW_AT_declaration attribute.
   bool declaration_;
@@ -377,16 +349,16 @@ class DwarfCUToModule::GenericDIEHandler: public DIEHandler {
 
   // The value of the DW_AT_name attribute, or the empty string if the
   // DIE has no such attribute.
-  string name_attribute_;
+  StringView name_attribute_;
 
   // The demangled value of the DW_AT_MIPS_linkage_name attribute, or the empty
   // string if the DIE has no such attribute or its content could not be
   // demangled.
-  string demangled_name_;
+  StringView demangled_name_;
 
   // The non-demangled value of the DW_AT_MIPS_linkage_name attribute,
   // it its content count not be demangled.
-  string raw_name_;
+  StringView raw_name_;
 };
 
 void DwarfCUToModule::GenericDIEHandler::ProcessAttributeUnsigned(
@@ -445,19 +417,14 @@ void DwarfCUToModule::GenericDIEHandler::ProcessAttributeReference(
   }
 }
 
-string DwarfCUToModule::GenericDIEHandler::AddStringToPool(const string& str) {
-  pair<unordered_set<string>::iterator, bool> result =
-    cu_context_->file_context->file_private_->common_strings.insert(str);
-  return *result.first;
-}
-
 void DwarfCUToModule::GenericDIEHandler::ProcessAttributeString(
     enum DwarfAttribute attr,
     enum DwarfForm form,
     const string& data) {
   switch (attr) {
     case DW_AT_name:
-      name_attribute_ = AddStringToPool(data);
+      name_attribute_ =
+          cu_context_->file_context->module_->AddStringToPool(data);
       break;
     case DW_AT_MIPS_linkage_name:
     case DW_AT_linkage_name: {
@@ -466,15 +433,16 @@ void DwarfCUToModule::GenericDIEHandler::ProcessAttributeString(
           cu_context_->language->DemangleName(data, &demangled);
       switch (result) {
         case Language::kDemangleSuccess:
-          demangled_name_ = AddStringToPool(demangled);
+          demangled_name_ =
+              cu_context_->file_context->module_->AddStringToPool(demangled);
           break;
 
         case Language::kDemangleFailure:
           cu_context_->reporter->DemangleError(data);
           // fallthrough
         case Language::kDontDemangle:
-          demangled_name_.clear();
-          raw_name_ = AddStringToPool(data);
+          demangled_name_ = StringView();
+          raw_name_ = cu_context_->file_context->module_->AddStringToPool(data);
           break;
       }
       break;
@@ -483,11 +451,11 @@ void DwarfCUToModule::GenericDIEHandler::ProcessAttributeString(
   }
 }
 
-string DwarfCUToModule::GenericDIEHandler::ComputeQualifiedName() {
+StringView DwarfCUToModule::GenericDIEHandler::ComputeQualifiedName() {
   // Use the demangled name, if one is available. Demangled names are
   // preferable to those inferred from the DWARF structure because they
   // include argument types.
-  const string* qualified_name = NULL;
+  StringView* qualified_name = nullptr;
   if (!demangled_name_.empty()) {
     // Found it is this DIE.
     qualified_name = &demangled_name_;
@@ -496,37 +464,39 @@ string DwarfCUToModule::GenericDIEHandler::ComputeQualifiedName() {
     qualified_name = &specification_->qualified_name;
   }
 
-  const string* unqualified_name = NULL;
-  const string* enclosing_name;
+  StringView* unqualified_name = nullptr;
+  StringView* enclosing_name = nullptr;
   if (!qualified_name) {
     // Find the unqualified name. If the DIE has its own DW_AT_name
     // attribute, then use that; otherwise, check the specification.
-    if (!name_attribute_.empty())
+    if (!name_attribute_.empty()) {
       unqualified_name = &name_attribute_;
-    else if (specification_)
+    } else if (specification_) {
       unqualified_name = &specification_->unqualified_name;
-    else if (!raw_name_.empty())
+    } else if (!raw_name_.empty()) {
       unqualified_name = &raw_name_;
+    }
 
     // Find the name of the enclosing context. If this DIE has a
     // specification, it's the specification's enclosing context that
     // counts; otherwise, use this DIE's context.
-    if (specification_)
+    if (specification_) {
       enclosing_name = &specification_->enclosing_name;
-    else
+    } else {
       enclosing_name = &parent_context_->name;
+    }
   }
 
   // Prepare the return value before upcoming mutations possibly invalidate the
   // existing pointers.
   string return_value;
   if (qualified_name) {
-    return_value = *qualified_name;
+    return_value = qualified_name->str();
   } else if (unqualified_name && enclosing_name) {
     // Combine the enclosing name and unqualified name to produce our
     // own fully-qualified name.
-    return_value = cu_context_->language->MakeQualifiedName(*enclosing_name,
-                                                            *unqualified_name);
+    return_value = cu_context_->language->MakeQualifiedName(
+        enclosing_name->str(), unqualified_name->str());
   }
 
   // If this DIE was marked as a declaration, record its names in the
@@ -543,7 +513,7 @@ string DwarfCUToModule::GenericDIEHandler::ComputeQualifiedName() {
     cu_context_->file_context->file_private_->specifications[offset_] = spec;
   }
 
-  return return_value;
+  return cu_context_->file_context->module_->AddStringToPool(return_value);
 }
 
 static bool IsEmptyRange(const vector<Module::Range>& ranges) {
@@ -585,7 +555,7 @@ class DwarfCUToModule::InlineHandler : public GenericDIEHandler {
  private:
   // The fully-qualified name, as derived from name_attribute_,
   // specification_, parent_context_. Computed in EndAttributes.
-  string name_;
+  StringView name_;
   uint64_t low_pc_;            // DW_AT_low_pc
   uint64_t high_pc_;           // DW_AT_high_pc
   DwarfForm high_pc_form_;     // DW_AT_high_pc can be length or address.
@@ -644,7 +614,8 @@ bool DwarfCUToModule::InlineHandler::EndAttributes() {
     // We haven't seen the abstract origin yet, which might appears later and we
     // will fix the name after calling
     // InlineOriginMap::GetOrCreateInlineOrigin with right name.
-    name_ = "<name omitted>";
+    name_ =
+        cu_context_->file_context->module_->AddStringToPool("<name omitted>");
   }
   return true;
 }
@@ -698,13 +669,19 @@ void DwarfCUToModule::InlineHandler::Finish() {
 // A handler class for DW_TAG_subprogram DIEs.
 class DwarfCUToModule::FuncHandler: public GenericDIEHandler {
  public:
-  FuncHandler(CUContext* cu_context, DIEContext* parent_context,
-              uint64_t offset, bool handle_inline)
+  FuncHandler(CUContext* cu_context,
+              DIEContext* parent_context,
+              uint64_t offset,
+              bool handle_inline)
       : GenericDIEHandler(cu_context, parent_context, offset),
-        low_pc_(0), high_pc_(0), high_pc_form_(DW_FORM_addr),
-        ranges_form_(DW_FORM_sec_offset), ranges_data_(0),
-        decl_file_data_(UINT64_MAX), inline_(false), 
-        handle_inline_(handle_inline) { }
+        low_pc_(0),
+        high_pc_(0),
+        high_pc_form_(DW_FORM_addr),
+        ranges_form_(DW_FORM_sec_offset),
+        ranges_data_(0),
+        decl_file_data_(UINT64_MAX),
+        inline_(false),
+        handle_inline_(handle_inline) {}
 
   void ProcessAttributeUnsigned(enum DwarfAttribute attr,
                                 enum DwarfForm form,
@@ -719,7 +696,7 @@ class DwarfCUToModule::FuncHandler: public GenericDIEHandler {
  private:
   // The fully-qualified name, as derived from name_attribute_,
   // specification_, parent_context_.  Computed in EndAttributes.
-  string name_;
+  StringView name_;
   uint64_t low_pc_, high_pc_; // DW_AT_low_pc, DW_AT_high_pc
   DwarfForm high_pc_form_; // DW_AT_high_pc can be length or address.
   DwarfForm ranges_form_; // DW_FORM_sec_offset or DW_FORM_rnglistx
@@ -841,6 +818,8 @@ void DwarfCUToModule::FuncHandler::Finish() {
     }
   }
 
+  StringView name_omitted =
+      cu_context_->file_context->module_->AddStringToPool("<name omitted>");
   bool empty_range = IsEmptyRange(ranges);
   // Did we collect the information we need?  Not all DWARF function
   // entries are non-empty (for example, inlined functions that were never
@@ -848,16 +827,9 @@ void DwarfCUToModule::FuncHandler::Finish() {
   // bytes.
   if (!empty_range) {
     low_pc_ = ranges.front().address;
-
     // Malformed DWARF may omit the name, but all Module::Functions must
     // have names.
-    string name;
-    if (!name_.empty()) {
-      name = name_;
-    } else {
-      name = "<name omitted>";
-    }
-
+    StringView name = name_.empty() ? name_omitted : name_;
     // Create a Module::Function based on the data we've gathered, and
     // add it to the functions_ list.
     scoped_ptr<Module::Function> func(new Module::Function(name, low_pc_));
@@ -880,20 +852,20 @@ void DwarfCUToModule::FuncHandler::Finish() {
     }
   } else if (inline_) {
     AbstractOrigin origin(name_);
-    cu_context_->file_context->file_private_->origins[offset_] = origin;
+    cu_context_->file_context->file_private_->origins.insert({offset_, origin});
   }
 
   // Only keep track of DW_TAG_subprogram which have the attributes we are
   // interested.
   if (handle_inline_ &&
       (!empty_range || inline_ || decl_file_data_ != UINT64_MAX)) {
+    StringView name = name_.empty() ? name_omitted : name_;
     uint64_t offset =
         specification_offset_ != 0 ? specification_offset_ : offset_;
     cu_context_->file_context->module_->inline_origin_map.SetReference(offset_,
                                                                        offset);
     cu_context_->file_context->module_->inline_origin_map
-        .GetOrCreateInlineOrigin(offset_,
-                                 name_.empty() ? "<name omitted>" : name_);
+        .GetOrCreateInlineOrigin(offset_, name);
     if (decl_file_data_ != UINT64_MAX)
       cu_context_->inline_origins[decl_file_data_].push_back(offset_);
   }
@@ -993,7 +965,7 @@ void DwarfCUToModule::WarningReporter::UncoveredFunction(
   UncoveredHeading();
   fprintf(stderr, "    function%s: %s\n",
           IsEmptyRange(function.ranges) ? " (zero-length)" : "",
-          function.name.c_str());
+          function.name.str().c_str());
 }
 
 void DwarfCUToModule::WarningReporter::UncoveredLine(const Module::Line& line) {

src/common/module.cc

@@ -32,6 +32,7 @@
 // module.cc: Implement google_breakpad::Module.  See module.h.
 
 #include "common/module.h"
+#include "common/string_view.h"
 
 #include <assert.h>
 #include <errno.h>
@@ -51,7 +52,7 @@ using std::unique_ptr;
 
 Module::InlineOrigin* Module::InlineOriginMap::GetOrCreateInlineOrigin(
     uint64_t offset,
-    const string& name) {
+    StringView name) {
   uint64_t specification_offset = references_[offset];
   // Find the root offset.
   auto iter = references_.find(specification_offset);

src/common/module.h

@@ -46,7 +46,9 @@
 #include <string>
 #include <vector>
 
+#include "common/string_view.h"
 #include "common/symbol_data.h"
+#include "common/unordered.h"
 #include "common/using_std_string.h"
 #include "google_breakpad/common/breakpad_types.h"
 
@@ -101,7 +103,7 @@ class Module {
 
   // A function.
   struct Function {
-    Function(const string& name_input, const Address& address_input) :
+    Function(StringView name_input, const Address& address_input) :
         name(name_input), address(address_input), parameter_size(0) {}
 
     // For sorting by address.  (Not style-guide compliant, but it's
@@ -111,7 +113,7 @@ class Module {
     }
 
     // The function's name.
-    string name;
+    StringView name;
 
     // The start address and the address ranges covered by the function.
     const Address address;
@@ -129,15 +131,14 @@ class Module {
   };
 
   struct InlineOrigin {
-    explicit InlineOrigin(const string& name)
-        : id(-1), name(name), file(nullptr) {}
+    explicit InlineOrigin(StringView name): id(-1), name(name), file(nullptr) {}
 
     // A unique id for each InlineOrigin object. INLINE records use the id to
     // refer to its INLINE_ORIGIN record.
     int id;
 
     // The inlined function's name.
-    string name;
+    StringView name;
 
     File* file;
 
@@ -175,7 +176,7 @@ class Module {
   class InlineOriginMap {
    public:
     // Add INLINE ORIGIN to the module. Return a pointer to origin .
-    InlineOrigin* GetOrCreateInlineOrigin(uint64_t offset, const string& name);
+    InlineOrigin* GetOrCreateInlineOrigin(uint64_t offset, StringView name);
 
     // offset is the offset of a DW_TAG_subprogram. specification_offset is the
     // value of its DW_AT_specification or equals to offset if
@@ -382,6 +383,13 @@ class Module {
   // established by SetLoadAddress.
   bool Write(std::ostream& stream, SymbolData symbol_data);
 
+  // Place the name in the global set of strings. Return a StringView points to
+  // a string inside the pool.
+  StringView AddStringToPool(const string& str) {
+    auto result = common_strings_.insert(str);
+    return *(result.first);
+  }
+
   string name() const { return name_; }
   string os() const { return os_; }
   string architecture() const { return architecture_; }
@@ -443,6 +451,8 @@ class Module {
   // The module owns all the externs that have been added to it;
   // destroying the module frees the Externs these point to.
   ExternSet externs_;
+
+  unordered_set<string> common_strings_;
 };
 
 }  // namespace google_breakpad

src/common/stabs_to_module.cc

@@ -90,7 +90,8 @@ bool StabsToModule::EndCompilationUnit(uint64_t address) {
 bool StabsToModule::StartFunction(const string& name,
                                   uint64_t address) {
   assert(!current_function_);
-  Module::Function *f = new Module::Function(Demangle(name), address);
+  Module::Function* f =
+      new Module::Function(module_->AddStringToPool(Demangle(name)), address);
   Module::Range r(address, 0); // We compute this in StabsToModule::Finalize().
   f->ranges.push_back(r);
   f->parameter_size = 0; // We don't provide this information.

src/common/string_view.h

@@ -0,0 +1,113 @@
+// Copyright (c) 2021 Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef COMMON_STRING_VIEW_H__
+#define COMMON_STRING_VIEW_H__
+
+#include <cassert>
+#include <cstring>
+#include <ostream>
+#include "common/using_std_string.h"
+
+namespace google_breakpad {
+
+// A StringView is a string reference to a string object, but not own the
+// string object.
+class StringView {
+ private:
+  // The start of the string, in an external buffer. It doesn't have to be
+  // null-terminated.
+  const char* data_ = "";
+
+  size_t length_ = 0;
+
+ public:
+  // Construct an empty StringView.
+  StringView() = default;
+
+  // Disallow construct StringView from nullptr.
+  StringView(nullptr_t) = delete;
+
+  // Construct a StringView from a cstring.
+  StringView(const char* str) : data_(str) {
+    assert(str);
+    length_ = strlen(str);
+  }
+
+  // Construct a StringView from a cstring with fixed length.
+  StringView(const char* str, size_t length) : data_(str), length_(length) {
+    assert(str);
+  }
+
+  // Construct a StringView from an std::string.
+  StringView(const string& str) : data_(str.data()), length_(str.length()) {}
+
+  string str() const { return string(data_, length_); }
+
+  const char* data() const { return data_; }
+
+  bool empty() const { return length_ == 0; }
+
+  size_t size() const { return length_; }
+
+  int compare(StringView rhs) const {
+    size_t min_len = std::min(size(), rhs.size());
+    int res = memcmp(data_, rhs.data(), min_len);
+    if (res != 0)
+      return res;
+    if (size() == rhs.size())
+      return 0;
+    return size() < rhs.size() ? -1 : 1;
+  }
+};
+
+inline bool operator==(StringView lhs, StringView rhs) {
+  return lhs.compare(rhs) == 0;
+}
+
+inline bool operator!=(StringView lhs, StringView rhs) {
+  return lhs.compare(rhs) != 0;
+}
+
+inline bool operator<(StringView lhs, StringView rhs) {
+  return lhs.compare(rhs) < 0;
+}
+
+inline bool operator>(StringView lhs, StringView rhs) {
+  return lhs.compare(rhs) > 0;
+}
+
+inline std::ostream& operator<<(std::ostream& os, StringView s) {
+  os << s.str();
+  return os;
+}
+
+}  // namespace google_breakpad
+
+#endif  // COMMON_STRING_VIEW_H__