Add user minidump stream support for ELF

This is very similar to the windows implementation in
module_snapshot_win.cc.

Bug: crashpad:95
Change-Id: I3858e8bb0009c95395bfb7ca3855c3d937fd49d5
Reviewed-on: https://chromium-review.googlesource.com/c/crashpad/crashpad/+/1641588
Commit-Queue: Clark DuVall <cduvall@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>

client/crashpad_info.h

@@ -208,7 +208,7 @@ struct CrashpadInfo {
   //! Note that streams will appear in the minidump in the reverse order to
   //! which they are added.
   //!
-  //! TODO(scottmg) This is currently only supported on Windows.
+  //! TODO(scottmg) This is currently not supported on Mac.
   //!
   //! \param[in] stream_type The stream type identifier to use. This should be
   //!     normally be larger than `MINIDUMP_STREAM_TYPE::LastReservedStream`

snapshot/elf/module_snapshot_elf.cc

@@ -20,6 +20,7 @@
 
 #include "base/files/file_path.h"
 #include "snapshot/crashpad_types/image_annotation_reader.h"
+#include "snapshot/memory_snapshot_generic.h"
 #include "util/misc/elf_note_types.h"
 
 namespace crashpad {
@@ -28,14 +29,17 @@ namespace internal {
 ModuleSnapshotElf::ModuleSnapshotElf(const std::string& name,
                                      ElfImageReader* elf_reader,
                                      ModuleSnapshot::ModuleType type,
-                                     ProcessMemoryRange* process_memory_range)
+                                     ProcessMemoryRange* process_memory_range,
+                                     const ProcessMemory* process_memory)
     : ModuleSnapshot(),
       name_(name),
       elf_reader_(elf_reader),
       process_memory_range_(process_memory_range),
+      process_memory_(process_memory),
       crashpad_info_(),
       type_(type),
-      initialized_() {}
+      initialized_(),
+      streams_() {}
 
 ModuleSnapshotElf::~ModuleSnapshotElf() = default;
 
@@ -216,7 +220,33 @@ std::set<CheckedRange<uint64_t>> ModuleSnapshotElf::ExtraMemoryRanges() const {
 
 std::vector<const UserMinidumpStream*>
 ModuleSnapshotElf::CustomMinidumpStreams() const {
-  return std::vector<const UserMinidumpStream*>();
+  INITIALIZATION_STATE_DCHECK_VALID(initialized_);
+  streams_.clear();
+
+  std::vector<const UserMinidumpStream*> result;
+  if (!crashpad_info_)
+    return result;
+
+  for (uint64_t cur = crashpad_info_->UserDataMinidumpStreamHead(); cur;) {
+    internal::UserDataMinidumpStreamListEntry list_entry;
+    if (!process_memory_->Read(cur, sizeof(list_entry), &list_entry)) {
+      LOG(WARNING) << "could not read user data stream entry from " << name_;
+      return result;
+    }
+
+    if (list_entry.size != 0) {
+      auto memory = std::make_unique<internal::MemorySnapshotGeneric>();
+      memory->Initialize(
+          process_memory_, list_entry.base_address, list_entry.size);
+      streams_.push_back(std::make_unique<UserMinidumpStream>(
+          list_entry.stream_type, memory.release()));
+      result.push_back(streams_.back().get());
+    }
+
+    cur = list_entry.next;
+  }
+
+  return result;
 }
 
 }  // namespace internal

snapshot/elf/module_snapshot_elf.h

@@ -41,11 +41,15 @@ class ModuleSnapshotElf final : public ModuleSnapshot {
   //! \param[in] name The pathname used to load the module from disk.
   //! \param[in] elf_reader An image reader for the module.
   //! \param[in] type The module's type.
-  //! \param[in] process_memory_range A memory reader for the target process.
+  //! \param[in] process_memory_range A memory reader giving protected access
+  //!     to the target process.
+  //! \param[in] process_memory A memory reader for the target process which can
+  //!     be used to initialize a MemorySnapshot.
   ModuleSnapshotElf(const std::string& name,
                     ElfImageReader* elf_reader,
                     ModuleSnapshot::ModuleType type,
-                    ProcessMemoryRange* process_memory_range);
+                    ProcessMemoryRange* process_memory_range,
+                    const ProcessMemory* process_memory);
   ~ModuleSnapshotElf() override;
 
   //! \brief Initializes the object.
@@ -88,9 +92,12 @@ class ModuleSnapshotElf final : public ModuleSnapshot {
   std::string name_;
   ElfImageReader* elf_reader_;
   ProcessMemoryRange* process_memory_range_;
+  const ProcessMemory* process_memory_;
   std::unique_ptr<CrashpadInfoReader> crashpad_info_;
   ModuleType type_;
   InitializationStateDcheck initialized_;
+  // Too const-y: https://crashpad.chromium.org/bug/9.
+  mutable std::vector<std::unique_ptr<const UserMinidumpStream>> streams_;
 
   DISALLOW_COPY_AND_ASSIGN(ModuleSnapshotElf);
 };

snapshot/fuchsia/process_snapshot_fuchsia.cc

@@ -223,7 +223,8 @@ void ProcessSnapshotFuchsia::InitializeModules() {
         std::make_unique<internal::ModuleSnapshotElf>(reader_module.name,
                                                       reader_module.reader,
                                                       reader_module.type,
-                                                      &memory_range_);
+                                                      &memory_range_,
+                                                      process_reader_.Memory());
     if (module->Initialize()) {
       modules_.push_back(std::move(module));
     }

snapshot/linux/process_snapshot_linux.cc

@@ -273,7 +273,8 @@ void ProcessSnapshotLinux::InitializeModules() {
         std::make_unique<internal::ModuleSnapshotElf>(reader_module.name,
                                                       reader_module.elf_reader,
                                                       reader_module.type,
-                                                      &memory_range_);
+                                                      &memory_range_,
+                                                      process_reader_.Memory());
     if (module->Initialize()) {
       modules_.push_back(std::move(module));
     }