Revert "Revert "Add BacktraceOffline for offline backtracing.""

This reverts commit 5c0b797cfc7e1297895e66db8d3de4a924e9f463.

And statically link llvm libraries on host to remove dependency
on 32-bit llvm shared library which is not included in the prebuilt.

Bug: 22229391

Change-Id: I8210687655ee1809fd820ab2a6ca5dfaf3f9096d

7 files changed, 975 insertions, 0 deletions

diff --git a/libbacktrace/Android.build.mk b/libbacktrace/Android.build.mk
index 4983b55..8e63dab 100644
--- a/libbacktrace/Android.build.mk
+++ b/libbacktrace/Android.build.mk
@@ -69,7 +69,10 @@ LOCAL_LDLIBS := \
     $($(module)_ldlibs) \
     $($(module)_ldlibs_$(build_type)) \
 
+LOCAL_STRIP_MODULE := $($(module)_strip_module)
+
 ifeq ($(build_type),target)
+  include $(LLVM_DEVICE_BUILD_MK)
   include $(BUILD_$(build_target))
 endif
 
@@ -77,6 +80,7 @@ ifeq ($(build_type),host)
   # Only build if host builds are supported.
   ifeq ($(build_host),true)
     LOCAL_CFLAGS += -Wno-extern-c-compat -fno-omit-frame-pointer
+    include $(LLVM_HOST_BUILD_MK)
     include $(BUILD_HOST_$(build_target))
   endif
 endif
diff --git a/libbacktrace/Android.mk b/libbacktrace/Android.mk
index 395d677..9c6742e 100644
--- a/libbacktrace/Android.mk
+++ b/libbacktrace/Android.mk
@@ -25,6 +25,7 @@ libbacktrace_common_conlyflags := \
 
 libbacktrace_common_cppflags := \
 	-std=gnu++11 \
+	-I external/libunwind/include/tdep \
 
 # The latest clang (r230699) does not allow SP/PC to be declared in inline asm lists.
 libbacktrace_common_clang_cflags += \
@@ -37,6 +38,9 @@ build_host := true
 endif
 endif
 
+LLVM_ROOT_PATH := external/llvm
+include $(LLVM_ROOT_PATH)/llvm.mk
+
 #-------------------------------------------------------------------------
 # The libbacktrace library.
 #-------------------------------------------------------------------------
@@ -44,6 +48,7 @@ libbacktrace_src_files := \
 	Backtrace.cpp \
 	BacktraceCurrent.cpp \
 	BacktraceMap.cpp \
+	BacktraceOffline.cpp \
 	BacktracePtrace.cpp \
 	thread_utils.c \
 	ThreadEntry.cpp \
@@ -56,6 +61,20 @@ libbacktrace_shared_libraries := \
 	liblog \
 	libunwind \
 
+# Use shared llvm library on device to save space.
+libbacktrace_shared_libraries_target := \
+	libLLVM \
+
+# Use static llvm libraries on host to remove dependency on 32-bit llvm shared library
+# which is not included in the prebuilt.
+libbacktrace_static_libraries_host := \
+	libLLVMObject \
+	libLLVMBitReader \
+	libLLVMMC \
+	libLLVMMCParser \
+	libLLVMCore \
+	libLLVMSupport \
+
 libbacktrace_ldlibs_host := \
 	-lpthread \
 	-lrt \
@@ -86,6 +105,8 @@ libbacktrace_test_cflags := \
 libbacktrace_test_src_files := \
 	backtrace_testlib.c \
 
+libbacktrace_test_strip_module := false
+
 module := libbacktrace_test
 module_tag := debug
 build_type := target
@@ -107,6 +128,7 @@ backtrace_test_cflags_target := \
 	-DENABLE_PSS_TESTS \
 
 backtrace_test_src_files := \
+	backtrace_offline_test.cpp \
 	backtrace_test.cpp \
 	GetPss.cpp \
 	thread_utils.c \
@@ -120,6 +142,7 @@ backtrace_test_shared_libraries := \
 	libbacktrace \
 	libbase \
 	libcutils \
+	libunwind \
 
 backtrace_test_shared_libraries_target += \
 	libdl \
@@ -127,6 +150,8 @@ backtrace_test_shared_libraries_target += \
 backtrace_test_ldlibs_host += \
 	-ldl \
 
+backtrace_test_strip_module := false
+
 module := backtrace_test
 module_tag := debug
 build_type := target
diff --git a/libbacktrace/Backtrace.cpp b/libbacktrace/Backtrace.cpp
index 97f0ef4..9ead452 100644
--- a/libbacktrace/Backtrace.cpp
+++ b/libbacktrace/Backtrace.cpp
@@ -30,6 +30,7 @@
 #include <cutils/threads.h>
 
 #include "BacktraceLog.h"
+#include "BacktraceOffline.h"
 #include "thread_utils.h"
 #include "UnwindCurrent.h"
 #include "UnwindPtrace.h"
@@ -140,3 +141,8 @@ Backtrace* Backtrace::Create(pid_t pid, pid_t tid, BacktraceMap* map) {
     return new UnwindPtrace(pid, tid, map);
   }
 }
+
+Backtrace* Backtrace::CreateOffline(pid_t pid, pid_t tid, BacktraceMap* map,
+                                    const backtrace_stackinfo_t& stack, bool cache_file) {
+  return new BacktraceOffline(pid, tid, map, stack, cache_file);
+}
diff --git a/libbacktrace/BacktraceMap.cpp b/libbacktrace/BacktraceMap.cpp
index ca47f67..eac20fe 100644
--- a/libbacktrace/BacktraceMap.cpp
+++ b/libbacktrace/BacktraceMap.cpp
@@ -144,3 +144,13 @@ BacktraceMap* BacktraceMap::Create(pid_t pid, bool /*uncached*/) {
   return map;
 }
 #endif
+
+BacktraceMap* BacktraceMap::Create(pid_t pid, const std::vector<backtrace_map_t>& maps) {
+    BacktraceMap* backtrace_map = new BacktraceMap(pid);
+    backtrace_map->maps_.insert(backtrace_map->maps_.begin(), maps.begin(), maps.end());
+    std::sort(backtrace_map->maps_.begin(), backtrace_map->maps_.end(),
+            [](const backtrace_map_t& map1, const backtrace_map_t& map2) {
+              return map1.start < map2.start;
+            });
+    return backtrace_map;
+}
diff --git a/libbacktrace/BacktraceOffline.cpp b/libbacktrace/BacktraceOffline.cpp
new file mode 100644
index 0000000..27dfb83
--- /dev/null
+++ b/libbacktrace/BacktraceOffline.cpp
@@ -0,0 +1,636 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "BacktraceOffline.h"
+
+extern "C" {
+#define UNW_REMOTE_ONLY
+#include <dwarf.h>
+}
+
+#include <stdint.h>
+#include <string.h>
+#include <sys/types.h>
+#include <ucontext.h>
+#include <unistd.h>
+
+#include <string>
+#include <vector>
+
+#include <backtrace/Backtrace.h>
+#include <backtrace/BacktraceMap.h>
+
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wunused-parameter"
+
+#include <llvm/ADT/StringRef.h>
+#include <llvm/Object/Binary.h>
+#include <llvm/Object/ELFObjectFile.h>
+#include <llvm/Object/ObjectFile.h>
+
+#pragma clang diagnostic pop
+
+#include "BacktraceLog.h"
+
+void Space::Clear() {
+  start = 0;
+  end = 0;
+  data = nullptr;
+}
+
+size_t Space::Read(uint64_t addr, uint8_t* buffer, size_t size) {
+  if (addr >= start && addr < end) {
+    size_t read_size = std::min(size, static_cast<size_t>(end - addr));
+    memcpy(buffer, data + (addr - start), read_size);
+    return read_size;
+  }
+  return 0;
+}
+
+static int FindProcInfo(unw_addr_space_t addr_space, unw_word_t ip, unw_proc_info* proc_info,
+                        int need_unwind_info, void* arg) {
+  BacktraceOffline* backtrace = reinterpret_cast<BacktraceOffline*>(arg);
+  bool result = backtrace->FindProcInfo(addr_space, ip, proc_info, need_unwind_info);
+  return result ? 0 : -UNW_EINVAL;
+}
+
+static void PutUnwindInfo(unw_addr_space_t, unw_proc_info_t*, void*) {
+}
+
+static int GetDynInfoListAddr(unw_addr_space_t, unw_word_t*, void*) {
+  return -UNW_ENOINFO;
+}
+
+static int AccessMem(unw_addr_space_t, unw_word_t addr, unw_word_t* value, int write, void* arg) {
+  if (write == 1) {
+    return -UNW_EINVAL;
+  }
+  BacktraceOffline* backtrace = reinterpret_cast<BacktraceOffline*>(arg);
+  *value = 0;
+  size_t read_size = backtrace->Read(addr, reinterpret_cast<uint8_t*>(value), sizeof(unw_word_t));
+  // Strictly we should check if read_size matches sizeof(unw_word_t), but it is possible in
+  // .eh_frame_hdr that the section can end at a position not aligned in sizeof(unw_word_t), and
+  // we should permit the read at the end of the section.
+  return (read_size > 0u ? 0 : -UNW_EINVAL);
+}
+
+static int AccessReg(unw_addr_space_t, unw_regnum_t unwind_reg, unw_word_t* value, int write,
+                     void* arg) {
+  if (write == 1) {
+    return -UNW_EINVAL;
+  }
+  BacktraceOffline* backtrace = reinterpret_cast<BacktraceOffline*>(arg);
+  uint64_t reg_value;
+  bool result = backtrace->ReadReg(unwind_reg, &reg_value);
+  if (result) {
+    *value = static_cast<unw_word_t>(reg_value);
+  }
+  return result ? 0 : -UNW_EINVAL;
+}
+
+static int AccessFpReg(unw_addr_space_t, unw_regnum_t, unw_fpreg_t*, int, void*) {
+  return -UNW_EINVAL;
+}
+
+static int Resume(unw_addr_space_t, unw_cursor_t*, void*) {
+  return -UNW_EINVAL;
+}
+
+static int GetProcName(unw_addr_space_t, unw_word_t, char*, size_t, unw_word_t*, void*) {
+  return -UNW_EINVAL;
+}
+
+static unw_accessors_t accessors = {
+    .find_proc_info = FindProcInfo,
+    .put_unwind_info = PutUnwindInfo,
+    .get_dyn_info_list_addr = GetDynInfoListAddr,
+    .access_mem = AccessMem,
+    .access_reg = AccessReg,
+    .access_fpreg = AccessFpReg,
+    .resume = Resume,
+    .get_proc_name = GetProcName,
+};
+
+bool BacktraceOffline::Unwind(size_t num_ignore_frames, ucontext_t* context) {
+  if (context == nullptr) {
+    BACK_LOGW("The context is needed for offline backtracing.");
+    return false;
+  }
+  context_ = context;
+
+  unw_addr_space_t addr_space = unw_create_addr_space(&accessors, 0);
+  unw_cursor_t cursor;
+  int ret = unw_init_remote(&cursor, addr_space, this);
+  if (ret != 0) {
+    BACK_LOGW("unw_init_remote failed %d", ret);
+    unw_destroy_addr_space(addr_space);
+    return false;
+  }
+  size_t num_frames = 0;
+  do {
+    unw_word_t pc;
+    ret = unw_get_reg(&cursor, UNW_REG_IP, &pc);
+    if (ret < 0) {
+      BACK_LOGW("Failed to read IP %d", ret);
+      break;
+    }
+    unw_word_t sp;
+    ret = unw_get_reg(&cursor, UNW_REG_SP, &sp);
+    if (ret < 0) {
+      BACK_LOGW("Failed to read SP %d", ret);
+      break;
+    }
+
+    if (num_ignore_frames == 0) {
+      frames_.resize(num_frames + 1);
+      backtrace_frame_data_t* frame = &frames_[num_frames];
+      frame->num = num_frames;
+      frame->pc = static_cast<uintptr_t>(pc);
+      frame->sp = static_cast<uintptr_t>(sp);
+      frame->stack_size = 0;
+
+      if (num_frames > 0) {
+        backtrace_frame_data_t* prev = &frames_[num_frames - 1];
+        prev->stack_size = frame->sp - prev->sp;
+      }
+      frame->func_name = GetFunctionName(frame->pc, &frame->func_offset);
+      FillInMap(frame->pc, &frame->map);
+      num_frames++;
+    } else {
+      num_ignore_frames--;
+    }
+    ret = unw_step(&cursor);
+  } while (ret > 0 && num_frames < MAX_BACKTRACE_FRAMES);
+
+  unw_destroy_addr_space(addr_space);
+  context_ = nullptr;
+  return true;
+}
+
+bool BacktraceOffline::ReadWord(uintptr_t ptr, word_t* out_value) {
+  size_t bytes_read = Read(ptr, reinterpret_cast<uint8_t*>(out_value), sizeof(word_t));
+  return bytes_read == sizeof(word_t);
+}
+
+size_t BacktraceOffline::Read(uintptr_t addr, uint8_t* buffer, size_t bytes) {
+  // Normally, libunwind needs stack information and call frame information to do remote unwinding.
+  // If call frame information is stored in .debug_frame, libunwind can read it from file
+  // by itself. If call frame information is stored in .eh_frame, we need to provide data in
+  // .eh_frame/.eh_frame_hdr sections.
+  // The order of readings below doesn't matter, as the spaces don't overlap with each other.
+  size_t read_size = eh_frame_hdr_space_.Read(addr, buffer, bytes);
+  if (read_size != 0) {
+    return read_size;
+  }
+  read_size = eh_frame_space_.Read(addr, buffer, bytes);
+  if (read_size != 0) {
+    return read_size;
+  }
+  read_size = stack_space_.Read(addr, buffer, bytes);
+  return read_size;
+}
+
+static bool FileOffsetToVaddr(
+    const std::vector<DebugFrameInfo::EhFrame::ProgramHeader>& program_headers,
+    uint64_t file_offset, uint64_t* vaddr) {
+  for (auto& header : program_headers) {
+    if (file_offset >= header.file_offset && file_offset < header.file_offset + header.file_size) {
+      // TODO: Consider load_bias?
+      *vaddr = file_offset - header.file_offset + header.vaddr;
+      return true;
+    }
+  }
+  return false;
+}
+
+bool BacktraceOffline::FindProcInfo(unw_addr_space_t addr_space, uint64_t ip,
+                                    unw_proc_info_t* proc_info, int need_unwind_info) {
+  backtrace_map_t map;
+  FillInMap(ip, &map);
+  if (!BacktraceMap::IsValid(map)) {
+    return false;
+  }
+  const std::string& filename = map.name;
+  DebugFrameInfo* debug_frame = GetDebugFrameInFile(filename);
+  if (debug_frame == nullptr) {
+    return false;
+  }
+  if (debug_frame->is_eh_frame) {
+    uint64_t ip_offset = ip - map.start + map.offset;
+    uint64_t ip_vaddr;  // vaddr in the elf file.
+    bool result = FileOffsetToVaddr(debug_frame->eh_frame.program_headers, ip_offset, &ip_vaddr);
+    if (!result) {
+      return false;
+    }
+    // Calculate the addresses where .eh_frame_hdr and .eh_frame stay when the process was running.
+    eh_frame_hdr_space_.start = (ip - ip_vaddr) + debug_frame->eh_frame.eh_frame_hdr_vaddr;
+    eh_frame_hdr_space_.end =
+        eh_frame_hdr_space_.start + debug_frame->eh_frame.eh_frame_hdr_data.size();
+    eh_frame_hdr_space_.data = debug_frame->eh_frame.eh_frame_hdr_data.data();
+
+    eh_frame_space_.start = (ip - ip_vaddr) + debug_frame->eh_frame.eh_frame_vaddr;
+    eh_frame_space_.end = eh_frame_space_.start + debug_frame->eh_frame.eh_frame_data.size();
+    eh_frame_space_.data = debug_frame->eh_frame.eh_frame_data.data();
+
+    unw_dyn_info di;
+    memset(&di, '\0', sizeof(di));
+    di.start_ip = map.start;
+    di.end_ip = map.end;
+    di.format = UNW_INFO_FORMAT_REMOTE_TABLE;
+    di.u.rti.name_ptr = 0;
+    di.u.rti.segbase = eh_frame_hdr_space_.start;
+    di.u.rti.table_data =
+        eh_frame_hdr_space_.start + debug_frame->eh_frame.fde_table_offset_in_eh_frame_hdr;
+    di.u.rti.table_len = (eh_frame_hdr_space_.end - di.u.rti.table_data) / sizeof(unw_word_t);
+    int ret = dwarf_search_unwind_table(addr_space, ip, &di, proc_info, need_unwind_info, this);
+    return ret == 0;
+  }
+
+  eh_frame_hdr_space_.Clear();
+  eh_frame_space_.Clear();
+  unw_dyn_info_t di;
+  unw_word_t segbase = map.start - map.offset;
+  int found = dwarf_find_debug_frame(0, &di, ip, segbase, filename.c_str(), map.start, map.end);
+  if (found == 1) {
+    int ret = dwarf_search_unwind_table(addr_space, ip, &di, proc_info, need_unwind_info, this);
+    return ret == 0;
+  }
+  return false;
+}
+
+bool BacktraceOffline::ReadReg(size_t reg, uint64_t* value) {
+  bool result = true;
+#if defined(__arm__)
+  switch (reg) {
+    case UNW_ARM_R0:
+      *value = context_->uc_mcontext.arm_r0;
+      break;
+    case UNW_ARM_R1:
+      *value = context_->uc_mcontext.arm_r1;
+      break;
+    case UNW_ARM_R2:
+      *value = context_->uc_mcontext.arm_r2;
+      break;
+    case UNW_ARM_R3:
+      *value = context_->uc_mcontext.arm_r3;
+      break;
+    case UNW_ARM_R4:
+      *value = context_->uc_mcontext.arm_r4;
+      break;
+    case UNW_ARM_R5:
+      *value = context_->uc_mcontext.arm_r5;
+      break;
+    case UNW_ARM_R6:
+      *value = context_->uc_mcontext.arm_r6;
+      break;
+    case UNW_ARM_R7:
+      *value = context_->uc_mcontext.arm_r7;
+      break;
+    case UNW_ARM_R8:
+      *value = context_->uc_mcontext.arm_r8;
+      break;
+    case UNW_ARM_R9:
+      *value = context_->uc_mcontext.arm_r9;
+      break;
+    case UNW_ARM_R10:
+      *value = context_->uc_mcontext.arm_r10;
+      break;
+    case UNW_ARM_R11:
+      *value = context_->uc_mcontext.arm_fp;
+      break;
+    case UNW_ARM_R12:
+      *value = context_->uc_mcontext.arm_ip;
+      break;
+    case UNW_ARM_R13:
+      *value = context_->uc_mcontext.arm_sp;
+      break;
+    case UNW_ARM_R14:
+      *value = context_->uc_mcontext.arm_lr;
+      break;
+    case UNW_ARM_R15:
+      *value = context_->uc_mcontext.arm_pc;
+      break;
+    default:
+      result = false;
+  }
+#elif defined(__aarch64__)
+  if (reg <= UNW_AARCH64_PC) {
+    *value = context_->uc_mcontext.regs[reg];
+  } else {
+    result = false;
+  }
+#elif defined(__x86_64__)
+  switch (reg) {
+    case UNW_X86_64_R8:
+      *value = context_->uc_mcontext.gregs[REG_R8];
+      break;
+    case UNW_X86_64_R9:
+      *value = context_->uc_mcontext.gregs[REG_R9];
+      break;
+    case UNW_X86_64_R10:
+      *value = context_->uc_mcontext.gregs[REG_R10];
+      break;
+    case UNW_X86_64_R11:
+      *value = context_->uc_mcontext.gregs[REG_R11];
+      break;
+    case UNW_X86_64_R12:
+      *value = context_->uc_mcontext.gregs[REG_R12];
+      break;
+    case UNW_X86_64_R13:
+      *value = context_->uc_mcontext.gregs[REG_R13];
+      break;
+    case UNW_X86_64_R14:
+      *value = context_->uc_mcontext.gregs[REG_R14];
+      break;
+    case UNW_X86_64_R15:
+      *value = context_->uc_mcontext.gregs[REG_R15];
+      break;
+    case UNW_X86_64_RDI:
+      *value = context_->uc_mcontext.gregs[REG_RDI];
+      break;
+    case UNW_X86_64_RSI:
+      *value = context_->uc_mcontext.gregs[REG_RSI];
+      break;
+    case UNW_X86_64_RBP:
+      *value = context_->uc_mcontext.gregs[REG_RBP];
+      break;
+    case UNW_X86_64_RBX:
+      *value = context_->uc_mcontext.gregs[REG_RBX];
+      break;
+    case UNW_X86_64_RDX:
+      *value = context_->uc_mcontext.gregs[REG_RDX];
+      break;
+    case UNW_X86_64_RAX:
+      *value = context_->uc_mcontext.gregs[REG_RAX];
+      break;
+    case UNW_X86_64_RCX:
+      *value = context_->uc_mcontext.gregs[REG_RCX];
+      break;
+    case UNW_X86_64_RSP:
+      *value = context_->uc_mcontext.gregs[REG_RSP];
+      break;
+    case UNW_X86_64_RIP:
+      *value = context_->uc_mcontext.gregs[REG_RIP];
+      break;
+    default:
+      result = false;
+  }
+#elif defined(__i386__)
+  switch (reg) {
+    case UNW_X86_GS:
+      *value = context_->uc_mcontext.gregs[REG_GS];
+      break;
+    case UNW_X86_FS:
+      *value = context_->uc_mcontext.gregs[REG_FS];
+      break;
+    case UNW_X86_ES:
+      *value = context_->uc_mcontext.gregs[REG_ES];
+      break;
+    case UNW_X86_DS:
+      *value = context_->uc_mcontext.gregs[REG_DS];
+      break;
+    case UNW_X86_EAX:
+      *value = context_->uc_mcontext.gregs[REG_EAX];
+      break;
+    case UNW_X86_EBX:
+      *value = context_->uc_mcontext.gregs[REG_EBX];
+      break;
+    case UNW_X86_ECX:
+      *value = context_->uc_mcontext.gregs[REG_ECX];
+      break;
+    case UNW_X86_EDX:
+      *value = context_->uc_mcontext.gregs[REG_EDX];
+      break;
+    case UNW_X86_ESI:
+      *value = context_->uc_mcontext.gregs[REG_ESI];
+      break;
+    case UNW_X86_EDI:
+      *value = context_->uc_mcontext.gregs[REG_EDI];
+      break;
+    case UNW_X86_EBP:
+      *value = context_->uc_mcontext.gregs[REG_EBP];
+      break;
+    case UNW_X86_EIP:
+      *value = context_->uc_mcontext.gregs[REG_EIP];
+      break;
+    case UNW_X86_ESP:
+      *value = context_->uc_mcontext.gregs[REG_ESP];
+      break;
+    case UNW_X86_TRAPNO:
+      *value = context_->uc_mcontext.gregs[REG_TRAPNO];
+      break;
+    case UNW_X86_CS:
+      *value = context_->uc_mcontext.gregs[REG_CS];
+      break;
+    case UNW_X86_EFLAGS:
+      *value = context_->uc_mcontext.gregs[REG_EFL];
+      break;
+    case UNW_X86_SS:
+      *value = context_->uc_mcontext.gregs[REG_SS];
+      break;
+    default:
+      result = false;
+  }
+#endif
+  return result;
+}
+
+std::string BacktraceOffline::GetFunctionNameRaw(uintptr_t, uintptr_t* offset) {
+  // We don't have enough information to support this. And it is expensive.
+  *offset = 0;
+  return "";
+}
+
+std::unordered_map<std::string, std::unique_ptr<DebugFrameInfo>> BacktraceOffline::debug_frames_;
+std::unordered_set<std::string> BacktraceOffline::debug_frame_missing_files_;
+
+static DebugFrameInfo* ReadDebugFrameFromFile(const std::string& filename);
+
+DebugFrameInfo* BacktraceOffline::GetDebugFrameInFile(const std::string& filename) {
+  if (cache_file_) {
+    auto it = debug_frames_.find(filename);
+    if (it != debug_frames_.end()) {
+      return it->second.get();
+    }
+    if (debug_frame_missing_files_.find(filename) != debug_frame_missing_files_.end()) {
+      return nullptr;
+    }
+  }
+  DebugFrameInfo* debug_frame = ReadDebugFrameFromFile(filename);
+  if (cache_file_) {
+    if (debug_frame != nullptr) {
+      debug_frames_.emplace(filename, std::unique_ptr<DebugFrameInfo>(debug_frame));
+    } else {
+      debug_frame_missing_files_.insert(filename);
+    }
+  } else {
+    if (last_debug_frame_ != nullptr) {
+      delete last_debug_frame_;
+    }
+    last_debug_frame_ = debug_frame;
+  }
+  return debug_frame;
+}
+
+static bool OmitEncodedValue(uint8_t encode, const uint8_t*& p) {
+  if (encode == DW_EH_PE_omit) {
+    return 0;
+  }
+  uint8_t format = encode & 0x0f;
+  switch (format) {
+    case DW_EH_PE_ptr:
+      p += sizeof(unw_word_t);
+      break;
+    case DW_EH_PE_uleb128:
+    case DW_EH_PE_sleb128:
+      while ((*p & 0x80) != 0) {
+        ++p;
+      }
+      ++p;
+      break;
+    case DW_EH_PE_udata2:
+    case DW_EH_PE_sdata2:
+      p += 2;
+      break;
+    case DW_EH_PE_udata4:
+    case DW_EH_PE_sdata4:
+      p += 4;
+      break;
+    case DW_EH_PE_udata8:
+    case DW_EH_PE_sdata8:
+      p += 8;
+      break;
+    default:
+      return false;
+  }
+  return true;
+}
+
+static bool GetFdeTableOffsetInEhFrameHdr(const std::vector<uint8_t>& data,
+                                          uint64_t* table_offset_in_eh_frame_hdr) {
+  const uint8_t* p = data.data();
+  const uint8_t* end = p + data.size();
+  if (p + 4 > end) {
+    return false;
+  }
+  uint8_t version = *p++;
+  if (version != 1) {
+    return false;
+  }
+  uint8_t eh_frame_ptr_encode = *p++;
+  uint8_t fde_count_encode = *p++;
+  uint8_t fde_table_encode = *p++;
+
+  if (fde_table_encode != (DW_EH_PE_datarel | DW_EH_PE_sdata4)) {
+    return false;
+  }
+
+  if (!OmitEncodedValue(eh_frame_ptr_encode, p) || !OmitEncodedValue(fde_count_encode, p)) {
+    return false;
+  }
+  if (p >= end) {
+    return false;
+  }
+  *table_offset_in_eh_frame_hdr = p - data.data();
+  return true;
+}
+
+using ProgramHeader = DebugFrameInfo::EhFrame::ProgramHeader;
+
+template <class ELFT>
+DebugFrameInfo* ReadDebugFrameFromELFFile(const llvm::object::ELFFile<ELFT>* elf) {
+  bool has_eh_frame_hdr = false;
+  uint64_t eh_frame_hdr_vaddr = 0;
+  std::vector<uint8_t> eh_frame_hdr_data;
+  bool has_eh_frame = false;
+  uint64_t eh_frame_vaddr = 0;
+  std::vector<uint8_t> eh_frame_data;
+
+  for (auto it = elf->begin_sections(); it != elf->end_sections(); ++it) {
+    llvm::ErrorOr<llvm::StringRef> name = elf->getSectionName(&*it);
+    if (name) {
+      if (name.get() == ".debug_frame") {
+        DebugFrameInfo* debug_frame = new DebugFrameInfo;
+        debug_frame->is_eh_frame = false;
+        return debug_frame;
+      }
+      if (name.get() == ".eh_frame_hdr") {
+        has_eh_frame_hdr = true;
+        eh_frame_hdr_vaddr = it->sh_addr;
+        llvm::ErrorOr<llvm::ArrayRef<uint8_t>> data = elf->getSectionContents(&*it);
+        if (data) {
+          eh_frame_hdr_data.insert(eh_frame_hdr_data.begin(), data->data(),
+                                   data->data() + data->size());
+        } else {
+          return nullptr;
+        }
+      } else if (name.get() == ".eh_frame") {
+        has_eh_frame = true;
+        eh_frame_vaddr = it->sh_addr;
+        llvm::ErrorOr<llvm::ArrayRef<uint8_t>> data = elf->getSectionContents(&*it);
+        if (data) {
+          eh_frame_data.insert(eh_frame_data.begin(), data->data(), data->data() + data->size());
+        } else {
+          return nullptr;
+        }
+      }
+    }
+  }
+  if (!(has_eh_frame_hdr && has_eh_frame)) {
+    return nullptr;
+  }
+  uint64_t fde_table_offset;
+  if (!GetFdeTableOffsetInEhFrameHdr(eh_frame_hdr_data, &fde_table_offset)) {
+    return nullptr;
+  }
+
+  std::vector<ProgramHeader> program_headers;
+  for (auto it = elf->begin_program_headers(); it != elf->end_program_headers(); ++it) {
+    ProgramHeader header;
+    header.vaddr = it->p_vaddr;
+    header.file_offset = it->p_offset;
+    header.file_size = it->p_filesz;
+    program_headers.push_back(header);
+  }
+  DebugFrameInfo* debug_frame = new DebugFrameInfo;
+  debug_frame->is_eh_frame = true;
+  debug_frame->eh_frame.eh_frame_hdr_vaddr = eh_frame_hdr_vaddr;
+  debug_frame->eh_frame.eh_frame_vaddr = eh_frame_vaddr;
+  debug_frame->eh_frame.fde_table_offset_in_eh_frame_hdr = fde_table_offset;
+  debug_frame->eh_frame.eh_frame_hdr_data = std::move(eh_frame_hdr_data);
+  debug_frame->eh_frame.eh_frame_data = std::move(eh_frame_data);
+  debug_frame->eh_frame.program_headers = program_headers;
+  return debug_frame;
+}
+
+static DebugFrameInfo* ReadDebugFrameFromFile(const std::string& filename) {
+  auto owning_binary = llvm::object::createBinary(llvm::StringRef(filename));
+  if (owning_binary.getError()) {
+    return nullptr;
+  }
+  llvm::object::Binary* binary = owning_binary.get().getBinary();
+  auto obj = llvm::dyn_cast<llvm::object::ObjectFile>(binary);
+  if (obj == nullptr) {
+    return nullptr;
+  }
+  if (auto elf = llvm::dyn_cast<llvm::object::ELF32LEObjectFile>(obj)) {
+    return ReadDebugFrameFromELFFile(elf->getELFFile());
+  }
+  if (auto elf = llvm::dyn_cast<llvm::object::ELF64LEObjectFile>(obj)) {
+    return ReadDebugFrameFromELFFile(elf->getELFFile());
+  }
+  return nullptr;
+}
diff --git a/libbacktrace/BacktraceOffline.h b/libbacktrace/BacktraceOffline.h
new file mode 100644
index 0000000..42f826d
--- /dev/null
+++ b/libbacktrace/BacktraceOffline.h
@@ -0,0 +1,105 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef _LIBBACKTRACE_UNWIND_OFFLINE_H
+#define _LIBBACKTRACE_UNWIND_OFFLINE_H
+
+#include <libunwind.h>
+#include <stdint.h>
+#include <sys/types.h>
+#include <ucontext.h>
+
+#include <unordered_map>
+#include <unordered_set>
+
+#include <backtrace/Backtrace.h>
+
+struct Space {
+  uint64_t start;
+  uint64_t end;
+  const uint8_t* data;
+
+  Space() {
+    Clear();
+  }
+
+  void Clear();
+  size_t Read(uint64_t addr, uint8_t* buffer, size_t size);
+};
+
+struct DebugFrameInfo {
+  bool is_eh_frame;
+  struct EhFrame {
+    uint64_t eh_frame_hdr_vaddr;
+    uint64_t eh_frame_vaddr;
+    uint64_t fde_table_offset_in_eh_frame_hdr;
+    std::vector<uint8_t> eh_frame_hdr_data;
+    std::vector<uint8_t> eh_frame_data;
+    struct ProgramHeader {
+      uint64_t vaddr;
+      uint64_t file_offset;
+      uint64_t file_size;
+    };
+    std::vector<ProgramHeader> program_headers;
+  } eh_frame;
+};
+
+class BacktraceOffline : public Backtrace {
+ public:
+  BacktraceOffline(pid_t pid, pid_t tid, BacktraceMap* map, const backtrace_stackinfo_t& stack,
+                   bool cache_file)
+      : Backtrace(pid, tid, map),
+        cache_file_(cache_file),
+        context_(nullptr),
+        last_debug_frame_(nullptr) {
+    stack_space_.start = stack.start;
+    stack_space_.end = stack.end;
+    stack_space_.data = stack.data;
+  }
+
+  virtual ~BacktraceOffline() {
+    if (last_debug_frame_ != nullptr) {
+      delete last_debug_frame_;
+    }
+  }
+
+  bool Unwind(size_t num_ignore_frames, ucontext_t* context) override;
+
+  bool ReadWord(uintptr_t ptr, word_t* out_value) override;
+
+  size_t Read(uintptr_t addr, uint8_t* buffer, size_t bytes) override;
+
+  bool FindProcInfo(unw_addr_space_t addr_space, uint64_t ip, unw_proc_info_t* proc_info,
+                    int need_unwind_info);
+
+  bool ReadReg(size_t reg_index, uint64_t* value);
+
+ protected:
+  std::string GetFunctionNameRaw(uintptr_t pc, uintptr_t* offset) override;
+  DebugFrameInfo* GetDebugFrameInFile(const std::string& filename);
+
+  static std::unordered_map<std::string, std::unique_ptr<DebugFrameInfo>> debug_frames_;
+  static std::unordered_set<std::string> debug_frame_missing_files_;
+
+  bool cache_file_;
+  ucontext_t* context_;
+  Space eh_frame_hdr_space_;
+  Space eh_frame_space_;
+  Space stack_space_;
+  DebugFrameInfo* last_debug_frame_;
+};
+
+#endif  // _LIBBACKTRACE_BACKTRACE_OFFLINE_H
diff --git a/libbacktrace/backtrace_offline_test.cpp b/libbacktrace/backtrace_offline_test.cpp
new file mode 100644
index 0000000..88a3533
--- /dev/null
+++ b/libbacktrace/backtrace_offline_test.cpp
@@ -0,0 +1,189 @@
+#include <libunwind.h>
+#include <pthread.h>
+#include <stdint.h>
+#include <string.h>
+
+#include <functional>
+#include <memory>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include <backtrace/Backtrace.h>
+#include <backtrace/BacktraceMap.h>
+#include <cutils/threads.h>
+
+#include <gtest/gtest.h>
+
+extern "C" {
+// Prototypes for functions in the test library.
+int test_level_one(int, int, int, int, void (*)(void*), void*);
+int test_level_two(int, int, int, int, void (*)(void*), void*);
+int test_level_three(int, int, int, int, void (*)(void*), void*);
+int test_level_four(int, int, int, int, void (*)(void*), void*);
+int test_recursive_call(int, void (*)(void*), void*);
+}
+
+static volatile bool g_exit_flag = false;
+
+static void GetContextAndExit(void* arg) {
+  unw_context_t* unw_context = reinterpret_cast<unw_context_t*>(arg);
+  unw_getcontext(unw_context);
+  // Don't touch the stack anymore.
+  while (!g_exit_flag) {
+  }
+}
+
+struct OfflineThreadArg {
+  unw_context_t unw_context;
+  pid_t tid;
+  std::function<int(void (*)(void*), void*)> function;
+};
+
+static void* OfflineThreadFunc(void* arg) {
+  OfflineThreadArg* fn_arg = reinterpret_cast<OfflineThreadArg*>(arg);
+  fn_arg->tid = gettid();
+  fn_arg->function(GetContextAndExit, &fn_arg->unw_context);
+  return nullptr;
+}
+
+static ucontext_t GetUContextFromUnwContext(const unw_context_t& unw_context) {
+  ucontext_t ucontext;
+  memset(&ucontext, 0, sizeof(ucontext));
+#if defined(__arm__)
+  ucontext.uc_mcontext.arm_r0 = unw_context.regs[0];
+  ucontext.uc_mcontext.arm_r1 = unw_context.regs[1];
+  ucontext.uc_mcontext.arm_r2 = unw_context.regs[2];
+  ucontext.uc_mcontext.arm_r3 = unw_context.regs[3];
+  ucontext.uc_mcontext.arm_r4 = unw_context.regs[4];
+  ucontext.uc_mcontext.arm_r5 = unw_context.regs[5];
+  ucontext.uc_mcontext.arm_r6 = unw_context.regs[6];
+  ucontext.uc_mcontext.arm_r7 = unw_context.regs[7];
+  ucontext.uc_mcontext.arm_r8 = unw_context.regs[8];
+  ucontext.uc_mcontext.arm_r9 = unw_context.regs[9];
+  ucontext.uc_mcontext.arm_r10 = unw_context.regs[10];
+  ucontext.uc_mcontext.arm_fp = unw_context.regs[11];
+  ucontext.uc_mcontext.arm_ip = unw_context.regs[12];
+  ucontext.uc_mcontext.arm_sp = unw_context.regs[13];
+  ucontext.uc_mcontext.arm_lr = unw_context.regs[14];
+  ucontext.uc_mcontext.arm_pc = unw_context.regs[15];
+#else
+  ucontext.uc_mcontext = unw_context.uc_mcontext;
+#endif
+  return ucontext;
+}
+
+static void OfflineBacktraceFunctionCall(std::function<int(void (*)(void*), void*)> function,
+                                         std::vector<uintptr_t>* pc_values) {
+  // Create a thread to generate the needed stack and registers information.
+  g_exit_flag = false;
+  const size_t stack_size = 1024 * 1024;
+  void* stack = mmap(NULL, stack_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+  ASSERT_NE(MAP_FAILED, stack);
+  uintptr_t stack_addr = reinterpret_cast<uintptr_t>(stack);
+  pthread_attr_t attr;
+  ASSERT_EQ(0, pthread_attr_init(&attr));
+  ASSERT_EQ(0, pthread_attr_setstack(&attr, reinterpret_cast<void*>(stack), stack_size));
+  pthread_t thread;
+  OfflineThreadArg arg;
+  arg.function = function;
+  ASSERT_EQ(0, pthread_create(&thread, &attr, OfflineThreadFunc, &arg));
+  // Wait for the offline thread to generate the stack and unw_context information.
+  sleep(1);
+  // Copy the stack information.
+  std::vector<uint8_t> stack_data(reinterpret_cast<uint8_t*>(stack),
+                                  reinterpret_cast<uint8_t*>(stack) + stack_size);
+  g_exit_flag = true;
+  ASSERT_EQ(0, pthread_join(thread, nullptr));
+  ASSERT_EQ(0, munmap(stack, stack_size));
+
+  // Do offline backtrace.
+  std::unique_ptr<BacktraceMap> map(BacktraceMap::Create(getpid()));
+  ASSERT_TRUE(map != nullptr);
+
+  backtrace_stackinfo_t stack_info;
+  stack_info.start = stack_addr;
+  stack_info.end = stack_addr + stack_size;
+  stack_info.data = stack_data.data();
+
+  std::unique_ptr<Backtrace> backtrace(
+      Backtrace::CreateOffline(getpid(), arg.tid, map.get(), stack_info));
+  ASSERT_TRUE(backtrace != nullptr);
+
+  ucontext_t ucontext = GetUContextFromUnwContext(arg.unw_context);
+  ASSERT_TRUE(backtrace->Unwind(0, &ucontext));
+
+  // Collect pc values of the call stack frames.
+  for (size_t i = 0; i < backtrace->NumFrames(); ++i) {
+    pc_values->push_back(backtrace->GetFrame(i)->pc);
+  }
+}
+
+// Return the name of the function which matches the address. Although we don't know the
+// exact end of each function, it is accurate enough for the tests.
+static std::string FunctionNameForAddress(uintptr_t addr) {
+  struct FunctionSymbol {
+    std::string name;
+    uintptr_t start;
+    uintptr_t end;
+  };
+
+  static std::vector<FunctionSymbol> symbols;
+  if (symbols.empty()) {
+    symbols = std::vector<FunctionSymbol>{
+        {"unknown_start", 0, 0},
+        {"test_level_one", reinterpret_cast<uintptr_t>(&test_level_one), 0},
+        {"test_level_two", reinterpret_cast<uintptr_t>(&test_level_two), 0},
+        {"test_level_three", reinterpret_cast<uintptr_t>(&test_level_three), 0},
+        {"test_level_four", reinterpret_cast<uintptr_t>(&test_level_four), 0},
+        {"test_recursive_call", reinterpret_cast<uintptr_t>(&test_recursive_call), 0},
+        {"GetContextAndExit", reinterpret_cast<uintptr_t>(&GetContextAndExit), 0},
+        {"unknown_end", static_cast<uintptr_t>(-1), static_cast<uintptr_t>(-1)},
+    };
+    std::sort(
+        symbols.begin(), symbols.end(),
+        [](const FunctionSymbol& s1, const FunctionSymbol& s2) { return s1.start < s2.start; });
+    for (size_t i = 0; i + 1 < symbols.size(); ++i) {
+      symbols[i].end = symbols[i + 1].start;
+    }
+  }
+  for (auto& symbol : symbols) {
+    if (addr >= symbol.start && addr < symbol.end) {
+      return symbol.name;
+    }
+  }
+  return "";
+}
+
+TEST(libbacktrace, offline) {
+  std::function<int(void (*)(void*), void*)> function =
+      std::bind(test_level_one, 1, 2, 3, 4, std::placeholders::_1, std::placeholders::_2);
+  std::vector<uintptr_t> pc_values;
+  OfflineBacktraceFunctionCall(function, &pc_values);
+  ASSERT_FALSE(pc_values.empty());
+  ASSERT_LE(pc_values.size(), static_cast<size_t>(MAX_BACKTRACE_FRAMES));
+
+  size_t test_one_index = 0;
+  for (size_t i = 0; i < pc_values.size(); ++i) {
+    if (FunctionNameForAddress(pc_values[i]) == "test_level_one") {
+      test_one_index = i;
+      break;
+    }
+  }
+
+  ASSERT_GE(test_one_index, 3u);
+  ASSERT_EQ("test_level_one", FunctionNameForAddress(pc_values[test_one_index]));
+  ASSERT_EQ("test_level_two", FunctionNameForAddress(pc_values[test_one_index - 1]));
+  ASSERT_EQ("test_level_three", FunctionNameForAddress(pc_values[test_one_index - 2]));
+  ASSERT_EQ("test_level_four", FunctionNameForAddress(pc_values[test_one_index - 3]));
+}
+
+TEST(libbacktrace, offline_max_trace) {
+  std::function<int(void (*)(void*), void*)> function = std::bind(
+      test_recursive_call, MAX_BACKTRACE_FRAMES + 10, std::placeholders::_1, std::placeholders::_2);
+  std::vector<uintptr_t> pc_values;
+  OfflineBacktraceFunctionCall(function, &pc_values);
+  ASSERT_FALSE(pc_values.empty());
+  ASSERT_EQ(static_cast<size_t>(MAX_BACKTRACE_FRAMES), pc_values.size());
+  ASSERT_EQ("test_recursive_call", FunctionNameForAddress(pc_values.back()));
+}