Read .note.gnu.build-id.

This will be used by heapprofd to allow us to correlate build ids with
memory leaks in libraries and binaries.

Test: m
Test: host libunwindstack_test
Test: run unwind_info against my phone's libc.so (32/64) and compare
      to readelf Build ID output.

Bug: 120186412

Change-Id: I3cefd6cce9a8733509bf35b7175eb0f967783477

8 files changed, 443 insertions, 1 deletions

diff --git a/libunwindstack/Elf.cpp b/libunwindstack/Elf.cpp
index 4d72ead..5b586a2 100644
--- a/libunwindstack/Elf.cpp
+++ b/libunwindstack/Elf.cpp
@@ -140,6 +140,10 @@ bool Elf::GetGlobalVariable(const std::string& name, uint64_t* memory_address) {
   return true;
 }
 
+bool Elf::GetBuildID(std::string* build_id) {
+  return valid_ && interface_->GetBuildID(build_id);
+}
+
 void Elf::GetLastError(ErrorData* data) {
   if (valid_) {
     *data = interface_->last_error();
diff --git a/libunwindstack/ElfInterface.cpp b/libunwindstack/ElfInterface.cpp
index f59a472..d0af94a 100644
--- a/libunwindstack/ElfInterface.cpp
+++ b/libunwindstack/ElfInterface.cpp
@@ -237,6 +237,56 @@ void ElfInterface::ReadProgramHeaders(const EhdrType& ehdr, uint64_t* load_bias)
   }
 }
 
+template <typename NhdrType>
+bool ElfInterface::ReadBuildID(std::string* build_id) {
+  // Ensure there is no overflow in any of the calulations below.
+  uint64_t tmp;
+  if (__builtin_add_overflow(gnu_build_id_offset_, gnu_build_id_size_, &tmp)) {
+    return false;
+  }
+
+  uint64_t offset = 0;
+  while (offset < gnu_build_id_size_) {
+    if (gnu_build_id_size_ - offset < sizeof(NhdrType)) {
+      return false;
+    }
+    NhdrType hdr;
+    if (!memory_->ReadFully(gnu_build_id_offset_ + offset, &hdr, sizeof(hdr))) {
+      return false;
+    }
+    offset += sizeof(hdr);
+
+    if (gnu_build_id_size_ - offset < hdr.n_namesz) {
+      return false;
+    }
+    if (hdr.n_namesz > 0) {
+      std::string name(hdr.n_namesz, '\0');
+      if (!memory_->ReadFully(gnu_build_id_offset_ + offset, &(name[0]), hdr.n_namesz)) {
+        return false;
+      }
+
+      // Trim trailing \0 as GNU is stored as a C string in the ELF file.
+      if (name.back() == '\0')
+        name.resize(name.size() - 1);
+
+      // Align hdr.n_namesz to next power multiple of 4. See man 5 elf.
+      offset += (hdr.n_namesz + 3) & ~3;
+
+      if (name == "GNU" && hdr.n_type == NT_GNU_BUILD_ID) {
+        if (gnu_build_id_size_ - offset < hdr.n_descsz) {
+          return false;
+        }
+        build_id->resize(hdr.n_descsz);
+        return memory_->ReadFully(gnu_build_id_offset_ + offset, &(*build_id)[0],
+                                  hdr.n_descsz);
+      }
+    }
+    // Align hdr.n_descsz to next power multiple of 4. See man 5 elf.
+    offset += (hdr.n_descsz + 3) & ~3;
+  }
+  return false;
+}
+
 template <typename EhdrType, typename ShdrType>
 void ElfInterface::ReadSectionHeaders(const EhdrType& ehdr) {
   uint64_t offset = ehdr.e_shoff;
@@ -308,6 +358,15 @@ void ElfInterface::ReadSectionHeaders(const EhdrType& ehdr) {
       // In order to read soname, keep track of address to offset mapping.
       strtabs_.push_back(std::make_pair<uint64_t, uint64_t>(static_cast<uint64_t>(shdr.sh_addr),
                                                             static_cast<uint64_t>(shdr.sh_offset)));
+    } else if (shdr.sh_type == SHT_NOTE) {
+      if (shdr.sh_name < sec_size) {
+        std::string name;
+        if (memory_->ReadString(sec_offset + shdr.sh_name, &name) &&
+            name == ".note.gnu.build-id") {
+          gnu_build_id_offset_ = shdr.sh_offset;
+          gnu_build_id_size_ = shdr.sh_size;
+        }
+      }
     }
   }
 }
@@ -492,6 +551,9 @@ template void ElfInterface::ReadProgramHeaders<Elf64_Ehdr, Elf64_Phdr>(const Elf
 template void ElfInterface::ReadSectionHeaders<Elf32_Ehdr, Elf32_Shdr>(const Elf32_Ehdr&);
 template void ElfInterface::ReadSectionHeaders<Elf64_Ehdr, Elf64_Shdr>(const Elf64_Ehdr&);
 
+template bool ElfInterface::ReadBuildID<Elf32_Nhdr>(std::string*);
+template bool ElfInterface::ReadBuildID<Elf64_Nhdr>(std::string*);
+
 template bool ElfInterface::GetSonameWithTemplate<Elf32_Dyn>(std::string*);
 template bool ElfInterface::GetSonameWithTemplate<Elf64_Dyn>(std::string*);
 
diff --git a/libunwindstack/include/unwindstack/Elf.h b/libunwindstack/include/unwindstack/Elf.h
index e5b0a89..27f7201 100644
--- a/libunwindstack/include/unwindstack/Elf.h
+++ b/libunwindstack/include/unwindstack/Elf.h
@@ -65,6 +65,8 @@ class Elf {
 
   bool GetGlobalVariable(const std::string& name, uint64_t* memory_address);
 
+  bool GetBuildID(std::string* build_id);
+
   uint64_t GetRelPc(uint64_t pc, const MapInfo* map_info);
 
   bool Step(uint64_t rel_pc, uint64_t adjusted_rel_pc, Regs* regs, Memory* process_memory,
diff --git a/libunwindstack/include/unwindstack/ElfInterface.h b/libunwindstack/include/unwindstack/ElfInterface.h
index a45eba8..52992d9 100644
--- a/libunwindstack/include/unwindstack/ElfInterface.h
+++ b/libunwindstack/include/unwindstack/ElfInterface.h
@@ -62,6 +62,8 @@ class ElfInterface {
 
   virtual bool GetGlobalVariable(const std::string& name, uint64_t* memory_address) = 0;
 
+  virtual bool GetBuildID(std::string* build_id) = 0;
+
   virtual bool Step(uint64_t rel_pc, Regs* regs, Memory* process_memory, bool* finished);
 
   virtual bool IsValidPc(uint64_t pc);
@@ -85,6 +87,8 @@ class ElfInterface {
   uint64_t debug_frame_size() { return debug_frame_size_; }
   uint64_t gnu_debugdata_offset() { return gnu_debugdata_offset_; }
   uint64_t gnu_debugdata_size() { return gnu_debugdata_size_; }
+  uint64_t gnu_build_id_offset() { return gnu_build_id_offset_; }
+  uint64_t gnu_build_id_size() { return gnu_build_id_size_; }
 
   DwarfSection* eh_frame() { return eh_frame_.get(); }
   DwarfSection* debug_frame() { return debug_frame_.get(); }
@@ -123,6 +127,9 @@ class ElfInterface {
   template <typename EhdrType>
   static void GetMaxSizeWithTemplate(Memory* memory, uint64_t* size);
 
+  template <typename NhdrType>
+  bool ReadBuildID(std::string* build_id);
+
   Memory* memory_;
   std::unordered_map<uint64_t, LoadInfo> pt_loads_;
 
@@ -143,6 +150,9 @@ class ElfInterface {
   uint64_t gnu_debugdata_offset_ = 0;
   uint64_t gnu_debugdata_size_ = 0;
 
+  uint64_t gnu_build_id_offset_ = 0;
+  uint64_t gnu_build_id_size_ = 0;
+
   uint8_t soname_type_ = SONAME_UNKNOWN;
   std::string soname_;
 
@@ -182,6 +192,10 @@ class ElfInterface32 : public ElfInterface {
     return ElfInterface::GetGlobalVariableWithTemplate<Elf32_Sym>(name, memory_address);
   }
 
+  bool GetBuildID(std::string* build_id) {
+    return ElfInterface::ReadBuildID<Elf32_Nhdr>(build_id);
+  }
+
   static void GetMaxSize(Memory* memory, uint64_t* size) {
     GetMaxSizeWithTemplate<Elf32_Ehdr>(memory, size);
   }
@@ -212,6 +226,10 @@ class ElfInterface64 : public ElfInterface {
     return ElfInterface::GetGlobalVariableWithTemplate<Elf64_Sym>(name, memory_address);
   }
 
+  bool GetBuildID(std::string* build_id) {
+    return ElfInterface::ReadBuildID<Elf64_Nhdr>(build_id);
+  }
+
   static void GetMaxSize(Memory* memory, uint64_t* size) {
     GetMaxSizeWithTemplate<Elf64_Ehdr>(memory, size);
   }
diff --git a/libunwindstack/tests/ElfFake.h b/libunwindstack/tests/ElfFake.h
index a3bf5ce..c2bd0f6 100644
--- a/libunwindstack/tests/ElfFake.h
+++ b/libunwindstack/tests/ElfFake.h
@@ -72,6 +72,9 @@ class ElfInterfaceFake : public ElfInterface {
 
   bool GetFunctionName(uint64_t, std::string*, uint64_t*) override;
   bool GetGlobalVariable(const std::string&, uint64_t*) override;
+  bool GetBuildID(std::string*) override {
+    return false;
+  }
 
   bool Step(uint64_t, Regs*, Memory*, bool*) override;
 
diff --git a/libunwindstack/tests/ElfInterfaceTest.cpp b/libunwindstack/tests/ElfInterfaceTest.cpp
index 9326bff..6023dc4 100644
--- a/libunwindstack/tests/ElfInterfaceTest.cpp
+++ b/libunwindstack/tests/ElfInterfaceTest.cpp
@@ -116,6 +116,21 @@ class ElfInterfaceTest : public ::testing::Test {
   void InitSym(uint64_t offset, uint32_t value, uint32_t size, uint32_t name_offset,
                uint64_t sym_offset, const char* name);
 
+  template <typename Ehdr, typename Shdr, typename Nhdr, typename ElfInterfaceType>
+  void BuildID();
+
+  template <typename Ehdr, typename Shdr, typename Nhdr, typename ElfInterfaceType>
+  void BuildIDTwoNotes();
+
+  template <typename Ehdr, typename Shdr, typename Nhdr, typename ElfInterfaceType>
+  void BuildIDSectionTooSmallForName();
+
+  template <typename Ehdr, typename Shdr, typename Nhdr, typename ElfInterfaceType>
+  void BuildIDSectionTooSmallForDesc();
+
+  template <typename Ehdr, typename Shdr, typename Nhdr, typename ElfInterfaceType>
+  void BuildIDSectionTooSmallForHeader();
+
   MemoryFake memory_;
 };
 
@@ -898,7 +913,7 @@ void ElfInterfaceTest::InitSectionHeadersOffsets() {
 
   Ehdr ehdr = {};
   ehdr.e_shoff = offset;
-  ehdr.e_shnum = 6;
+  ehdr.e_shnum = 7;
   ehdr.e_shentsize = sizeof(Shdr);
   ehdr.e_shstrndx = 2;
   memory_.SetMemory(0, &ehdr, sizeof(ehdr));
@@ -958,10 +973,19 @@ void ElfInterfaceTest::InitSectionHeadersOffsets() {
   memory_.SetMemory(offset, &shdr, sizeof(shdr));
   offset += ehdr.e_shentsize;
 
+  memset(&shdr, 0, sizeof(shdr));
+  shdr.sh_type = SHT_NOTE;
+  shdr.sh_name = 0x500;
+  shdr.sh_offset = 0xb000;
+  shdr.sh_size = 0xf00;
+  memory_.SetMemory(offset, &shdr, sizeof(shdr));
+  offset += ehdr.e_shentsize;
+
   memory_.SetMemory(0xf100, ".debug_frame", sizeof(".debug_frame"));
   memory_.SetMemory(0xf200, ".gnu_debugdata", sizeof(".gnu_debugdata"));
   memory_.SetMemory(0xf300, ".eh_frame", sizeof(".eh_frame"));
   memory_.SetMemory(0xf400, ".eh_frame_hdr", sizeof(".eh_frame_hdr"));
+  memory_.SetMemory(0xf500, ".note.gnu.build-id", sizeof(".note.gnu.build-id"));
 
   uint64_t load_bias = 0;
   ASSERT_TRUE(elf->Init(&load_bias));
@@ -974,6 +998,8 @@ void ElfInterfaceTest::InitSectionHeadersOffsets() {
   EXPECT_EQ(0x800U, elf->eh_frame_size());
   EXPECT_EQ(0xa000U, elf->eh_frame_hdr_offset());
   EXPECT_EQ(0xf00U, elf->eh_frame_hdr_size());
+  EXPECT_EQ(0xb000U, elf->gnu_build_id_offset());
+  EXPECT_EQ(0xf00U, elf->gnu_build_id_size());
 }
 
 TEST_F(ElfInterfaceTest, init_section_headers_offsets32) {
@@ -1153,4 +1179,321 @@ TEST_F(ElfInterfaceTest, is_valid_pc_from_eh_frame) {
   EXPECT_FALSE(elf->IsValidPc(0x2a00));
 }
 
+template <typename Ehdr, typename Shdr, typename Nhdr, typename ElfInterfaceType>
+void ElfInterfaceTest::BuildID() {
+  std::unique_ptr<ElfInterfaceType> elf(new ElfInterfaceType(&memory_));
+
+  uint64_t offset = 0x2000;
+
+  Ehdr ehdr = {};
+  ehdr.e_shoff = offset;
+  ehdr.e_shnum = 3;
+  ehdr.e_shentsize = sizeof(Shdr);
+  ehdr.e_shstrndx = 2;
+  memory_.SetMemory(0, &ehdr, sizeof(ehdr));
+
+  offset += ehdr.e_shentsize;
+
+  char note_section[128];
+  Nhdr note_header = {};
+  note_header.n_namesz = 4;  // "GNU"
+  note_header.n_descsz = 8; // "BUILDID"
+  note_header.n_type = NT_GNU_BUILD_ID;
+  memcpy(&note_section, &note_header, sizeof(note_header));
+  size_t note_offset = sizeof(note_header);
+  memcpy(&note_section[note_offset], "GNU", sizeof("GNU"));
+  note_offset += sizeof("GNU");
+  memcpy(&note_section[note_offset], "BUILDID", sizeof("BUILDID"));
+  note_offset += sizeof("BUILDID");
+
+  Shdr shdr = {};
+  shdr.sh_type = SHT_NOTE;
+  shdr.sh_name = 0x500;
+  shdr.sh_offset = 0xb000;
+  shdr.sh_size = sizeof(note_section);
+  memory_.SetMemory(offset, &shdr, sizeof(shdr));
+  offset += ehdr.e_shentsize;
+
+  // The string data for section header names.
+  memset(&shdr, 0, sizeof(shdr));
+  shdr.sh_type = SHT_STRTAB;
+  shdr.sh_name = 0x20000;
+  shdr.sh_offset = 0xf000;
+  shdr.sh_size = 0x1000;
+  memory_.SetMemory(offset, &shdr, sizeof(shdr));
+  offset += ehdr.e_shentsize;
+
+  memory_.SetMemory(0xf500, ".note.gnu.build-id", sizeof(".note.gnu.build-id"));
+  memory_.SetMemory(0xb000, note_section, sizeof(note_section));
+
+  uint64_t load_bias = 0;
+  ASSERT_TRUE(elf->Init(&load_bias));
+  std::string build_id;
+  ASSERT_TRUE(elf->GetBuildID(&build_id));
+  EXPECT_STREQ(build_id.c_str(), "BUILDID");
+}
+
+template <typename Ehdr, typename Shdr, typename Nhdr, typename ElfInterfaceType>
+void ElfInterfaceTest::BuildIDTwoNotes() {
+  std::unique_ptr<ElfInterfaceType> elf(new ElfInterfaceType(&memory_));
+
+  uint64_t offset = 0x2000;
+
+  Ehdr ehdr = {};
+  ehdr.e_shoff = offset;
+  ehdr.e_shnum = 3;
+  ehdr.e_shentsize = sizeof(Shdr);
+  ehdr.e_shstrndx = 2;
+  memory_.SetMemory(0, &ehdr, sizeof(ehdr));
+
+  offset += ehdr.e_shentsize;
+
+  char note_section[128];
+  Nhdr note_header = {};
+  note_header.n_namesz = 8;  // "WRONG" aligned to 4
+  note_header.n_descsz = 8; // "BUILDID"
+  note_header.n_type = NT_GNU_BUILD_ID;
+  memcpy(&note_section, &note_header, sizeof(note_header));
+  size_t note_offset = sizeof(note_header);
+  memcpy(&note_section[note_offset], "WRONG", sizeof("WRONG"));
+  note_offset += 8;
+  memcpy(&note_section[note_offset], "BUILDID", sizeof("BUILDID"));
+  note_offset += sizeof("BUILDID");
+
+  note_header.n_namesz = 4;  // "GNU"
+  note_header.n_descsz = 8; // "BUILDID"
+  note_header.n_type = NT_GNU_BUILD_ID;
+  memcpy(&note_section[note_offset], &note_header, sizeof(note_header));
+  note_offset += sizeof(note_header);
+  memcpy(&note_section[note_offset], "GNU", sizeof("GNU"));
+  note_offset += sizeof("GNU");
+  memcpy(&note_section[note_offset], "BUILDID", sizeof("BUILDID"));
+  note_offset += sizeof("BUILDID");
+
+  Shdr shdr = {};
+  shdr.sh_type = SHT_NOTE;
+  shdr.sh_name = 0x500;
+  shdr.sh_offset = 0xb000;
+  shdr.sh_size = sizeof(note_section);
+  memory_.SetMemory(offset, &shdr, sizeof(shdr));
+  offset += ehdr.e_shentsize;
+
+  // The string data for section header names.
+  memset(&shdr, 0, sizeof(shdr));
+  shdr.sh_type = SHT_STRTAB;
+  shdr.sh_name = 0x20000;
+  shdr.sh_offset = 0xf000;
+  shdr.sh_size = 0x1000;
+  memory_.SetMemory(offset, &shdr, sizeof(shdr));
+  offset += ehdr.e_shentsize;
+
+  memory_.SetMemory(0xf500, ".note.gnu.build-id", sizeof(".note.gnu.build-id"));
+  memory_.SetMemory(0xb000, note_section, sizeof(note_section));
+
+  uint64_t load_bias = 0;
+  ASSERT_TRUE(elf->Init(&load_bias));
+  std::string build_id;
+  ASSERT_TRUE(elf->GetBuildID(&build_id));
+  EXPECT_STREQ(build_id.c_str(), "BUILDID");
+}
+
+template <typename Ehdr, typename Shdr, typename Nhdr, typename ElfInterfaceType>
+void ElfInterfaceTest::BuildIDSectionTooSmallForName () {
+  std::unique_ptr<ElfInterfaceType> elf(new ElfInterfaceType(&memory_));
+
+  uint64_t offset = 0x2000;
+
+  Ehdr ehdr = {};
+  ehdr.e_shoff = offset;
+  ehdr.e_shnum = 3;
+  ehdr.e_shentsize = sizeof(Shdr);
+  ehdr.e_shstrndx = 2;
+  memory_.SetMemory(0, &ehdr, sizeof(ehdr));
+
+  offset += ehdr.e_shentsize;
+
+  char note_section[128];
+  Nhdr note_header = {};
+  note_header.n_namesz = 4;  // "GNU"
+  note_header.n_descsz = 8; // "BUILDID"
+  note_header.n_type = NT_GNU_BUILD_ID;
+  memcpy(&note_section, &note_header, sizeof(note_header));
+  size_t note_offset = sizeof(note_header);
+  memcpy(&note_section[note_offset], "GNU", sizeof("GNU"));
+  note_offset += sizeof("GNU");
+  memcpy(&note_section[note_offset], "BUILDID", sizeof("BUILDID"));
+  note_offset += sizeof("BUILDID");
+
+  Shdr shdr = {};
+  shdr.sh_type = SHT_NOTE;
+  shdr.sh_name = 0x500;
+  shdr.sh_offset = 0xb000;
+  shdr.sh_size = sizeof(note_header) + 1;
+  memory_.SetMemory(offset, &shdr, sizeof(shdr));
+  offset += ehdr.e_shentsize;
+
+  // The string data for section header names.
+  memset(&shdr, 0, sizeof(shdr));
+  shdr.sh_type = SHT_STRTAB;
+  shdr.sh_name = 0x20000;
+  shdr.sh_offset = 0xf000;
+  shdr.sh_size = 0x1000;
+  memory_.SetMemory(offset, &shdr, sizeof(shdr));
+  offset += ehdr.e_shentsize;
+
+  memory_.SetMemory(0xf500, ".note.gnu.build-id", sizeof(".note.gnu.build-id"));
+  memory_.SetMemory(0xb000, note_section, sizeof(note_section));
+
+  uint64_t load_bias = 0;
+  ASSERT_TRUE(elf->Init(&load_bias));
+  std::string build_id;
+  ASSERT_FALSE(elf->GetBuildID(&build_id));
+}
+
+template <typename Ehdr, typename Shdr, typename Nhdr, typename ElfInterfaceType>
+void ElfInterfaceTest::BuildIDSectionTooSmallForDesc () {
+  std::unique_ptr<ElfInterfaceType> elf(new ElfInterfaceType(&memory_));
+
+  uint64_t offset = 0x2000;
+
+  Ehdr ehdr = {};
+  ehdr.e_shoff = offset;
+  ehdr.e_shnum = 3;
+  ehdr.e_shentsize = sizeof(Shdr);
+  ehdr.e_shstrndx = 2;
+  memory_.SetMemory(0, &ehdr, sizeof(ehdr));
+
+  offset += ehdr.e_shentsize;
+
+  char note_section[128];
+  Nhdr note_header = {};
+  note_header.n_namesz = 4;  // "GNU"
+  note_header.n_descsz = 8; // "BUILDID"
+  note_header.n_type = NT_GNU_BUILD_ID;
+  memcpy(&note_section, &note_header, sizeof(note_header));
+  size_t note_offset = sizeof(note_header);
+  memcpy(&note_section[note_offset], "GNU", sizeof("GNU"));
+  note_offset += sizeof("GNU");
+  memcpy(&note_section[note_offset], "BUILDID", sizeof("BUILDID"));
+  note_offset += sizeof("BUILDID");
+
+  Shdr shdr = {};
+  shdr.sh_type = SHT_NOTE;
+  shdr.sh_name = 0x500;
+  shdr.sh_offset = 0xb000;
+  shdr.sh_size = sizeof(note_header) + sizeof("GNU") + 1;
+  memory_.SetMemory(offset, &shdr, sizeof(shdr));
+  offset += ehdr.e_shentsize;
+
+  // The string data for section header names.
+  memset(&shdr, 0, sizeof(shdr));
+  shdr.sh_type = SHT_STRTAB;
+  shdr.sh_name = 0x20000;
+  shdr.sh_offset = 0xf000;
+  shdr.sh_size = 0x1000;
+  memory_.SetMemory(offset, &shdr, sizeof(shdr));
+  offset += ehdr.e_shentsize;
+
+  memory_.SetMemory(0xf500, ".note.gnu.build-id", sizeof(".note.gnu.build-id"));
+  memory_.SetMemory(0xb000, note_section, sizeof(note_section));
+
+  uint64_t load_bias = 0;
+  ASSERT_TRUE(elf->Init(&load_bias));
+  std::string build_id;
+  ASSERT_FALSE(elf->GetBuildID(&build_id));
+}
+
+template <typename Ehdr, typename Shdr, typename Nhdr, typename ElfInterfaceType>
+void ElfInterfaceTest::BuildIDSectionTooSmallForHeader () {
+  std::unique_ptr<ElfInterfaceType> elf(new ElfInterfaceType(&memory_));
+
+  uint64_t offset = 0x2000;
+
+  Ehdr ehdr = {};
+  ehdr.e_shoff = offset;
+  ehdr.e_shnum = 3;
+  ehdr.e_shentsize = sizeof(Shdr);
+  ehdr.e_shstrndx = 2;
+  memory_.SetMemory(0, &ehdr, sizeof(ehdr));
+
+  offset += ehdr.e_shentsize;
+
+  char note_section[128];
+  Nhdr note_header = {};
+  note_header.n_namesz = 4;  // "GNU"
+  note_header.n_descsz = 8; // "BUILDID"
+  note_header.n_type = NT_GNU_BUILD_ID;
+  memcpy(&note_section, &note_header, sizeof(note_header));
+  size_t note_offset = sizeof(note_header);
+  memcpy(&note_section[note_offset], "GNU", sizeof("GNU"));
+  note_offset += sizeof("GNU");
+  memcpy(&note_section[note_offset], "BUILDID", sizeof("BUILDID"));
+  note_offset += sizeof("BUILDID");
+
+  Shdr shdr = {};
+  shdr.sh_type = SHT_NOTE;
+  shdr.sh_name = 0x500;
+  shdr.sh_offset = 0xb000;
+  shdr.sh_size = sizeof(note_header) - 1;
+  memory_.SetMemory(offset, &shdr, sizeof(shdr));
+  offset += ehdr.e_shentsize;
+
+  // The string data for section header names.
+  memset(&shdr, 0, sizeof(shdr));
+  shdr.sh_type = SHT_STRTAB;
+  shdr.sh_name = 0x20000;
+  shdr.sh_offset = 0xf000;
+  shdr.sh_size = 0x1000;
+  memory_.SetMemory(offset, &shdr, sizeof(shdr));
+  offset += ehdr.e_shentsize;
+
+  memory_.SetMemory(0xf500, ".note.gnu.build-id", sizeof(".note.gnu.build-id"));
+  memory_.SetMemory(0xb000, note_section, sizeof(note_section));
+
+  uint64_t load_bias = 0;
+  ASSERT_TRUE(elf->Init(&load_bias));
+  std::string build_id;
+  ASSERT_FALSE(elf->GetBuildID(&build_id));
+}
+
+TEST_F(ElfInterfaceTest, build_id32) {
+  BuildID<Elf32_Ehdr, Elf32_Shdr, Elf32_Nhdr, ElfInterface32>();
+}
+
+TEST_F(ElfInterfaceTest, build_id64) {
+  BuildID<Elf64_Ehdr, Elf64_Shdr, Elf64_Nhdr, ElfInterface64>();
+}
+
+TEST_F(ElfInterfaceTest, build_id_two_notes32) {
+  BuildIDTwoNotes<Elf32_Ehdr, Elf32_Shdr, Elf32_Nhdr, ElfInterface32>();
+}
+
+TEST_F(ElfInterfaceTest, build_id_two_notes64) {
+  BuildIDTwoNotes<Elf64_Ehdr, Elf64_Shdr, Elf64_Nhdr, ElfInterface64>();
+}
+
+TEST_F(ElfInterfaceTest, build_id_section_too_small_for_name32) {
+  BuildIDSectionTooSmallForName<Elf32_Ehdr, Elf32_Shdr, Elf32_Nhdr, ElfInterface32>();
+}
+
+TEST_F(ElfInterfaceTest, build_id_section_too_small_for_name64) {
+  BuildIDSectionTooSmallForName<Elf64_Ehdr, Elf64_Shdr, Elf64_Nhdr, ElfInterface64>();
+}
+
+TEST_F(ElfInterfaceTest, build_id_section_too_small_for_desc32) {
+  BuildIDSectionTooSmallForDesc<Elf32_Ehdr, Elf32_Shdr, Elf32_Nhdr, ElfInterface32>();
+}
+
+TEST_F(ElfInterfaceTest, build_id_section_too_small_for_desc64) {
+  BuildIDSectionTooSmallForDesc<Elf64_Ehdr, Elf64_Shdr, Elf64_Nhdr, ElfInterface64>();
+}
+
+TEST_F(ElfInterfaceTest, build_id_section_too_small_for_header32) {
+  BuildIDSectionTooSmallForHeader<Elf32_Ehdr, Elf32_Shdr, Elf32_Nhdr, ElfInterface32>();
+}
+
+TEST_F(ElfInterfaceTest, build_id_section_too_small_for_header64) {
+  BuildIDSectionTooSmallForHeader<Elf64_Ehdr, Elf64_Shdr, Elf64_Nhdr, ElfInterface64>();
+}
+
 }  // namespace unwindstack
diff --git a/libunwindstack/tests/ElfTest.cpp b/libunwindstack/tests/ElfTest.cpp
index ccf8927..7766218 100644
--- a/libunwindstack/tests/ElfTest.cpp
+++ b/libunwindstack/tests/ElfTest.cpp
@@ -311,6 +311,7 @@ class ElfInterfaceMock : public ElfInterface {
   void InitHeaders(uint64_t) override {}
   bool GetSoname(std::string*) override { return false; }
   bool GetFunctionName(uint64_t, std::string*, uint64_t*) override { return false; }
+  bool GetBuildID(std::string*) override { return false; }
 
   MOCK_METHOD4(Step, bool(uint64_t, Regs*, Memory*, bool*));
   MOCK_METHOD2(GetGlobalVariable, bool(const std::string&, uint64_t*));
diff --git a/libunwindstack/tools/unwind_info.cpp b/libunwindstack/tools/unwind_info.cpp
index aebeb95..3f2dfb0 100644
--- a/libunwindstack/tools/unwind_info.cpp
+++ b/libunwindstack/tools/unwind_info.cpp
@@ -123,6 +123,15 @@ int GetElfInfo(const char* file, uint64_t offset) {
     printf("Soname: %s\n", soname.c_str());
   }
 
+  std::string build_id;
+  if (elf.GetBuildID(&build_id)) {
+    printf("Build ID: ");
+    for (size_t i = 0; i < build_id.size(); ++i) {
+      printf("%02hhx", build_id[i]);
+    }
+    printf("\n");
+  }
+
   ElfInterface* interface = elf.interface();
   if (elf.machine_type() == EM_ARM) {
     DumpArm(&elf, reinterpret_cast<ElfInterfaceArm*>(interface));