| // Copyright 2021 The Chromium Authors |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #include "base/profiler/chrome_unwinder_android.h" |
| |
| #include <algorithm> |
| |
| #include "base/check_op.h" |
| #include "base/memory/aligned_memory.h" |
| #include "base/notreached.h" |
| #include "base/numerics/checked_math.h" |
| #include "base/profiler/chrome_unwind_info_android.h" |
| |
| namespace base { |
| namespace { |
| |
| uintptr_t* GetRegisterPointer(RegisterContext* context, |
| uint8_t register_index) { |
| DCHECK_LE(register_index, 15); |
| static unsigned long RegisterContext::*const registers[16] = { |
| &RegisterContext::arm_r0, &RegisterContext::arm_r1, |
| &RegisterContext::arm_r2, &RegisterContext::arm_r3, |
| &RegisterContext::arm_r4, &RegisterContext::arm_r5, |
| &RegisterContext::arm_r6, &RegisterContext::arm_r7, |
| &RegisterContext::arm_r8, &RegisterContext::arm_r9, |
| &RegisterContext::arm_r10, &RegisterContext::arm_fp, |
| &RegisterContext::arm_ip, &RegisterContext::arm_sp, |
| &RegisterContext::arm_lr, &RegisterContext::arm_pc, |
| }; |
| return reinterpret_cast<uintptr_t*>(&(context->*registers[register_index])); |
| } |
| |
| // Pops the value on the top of stack out and assign it to target register. |
| // This is equivalent to arm instruction `Pop r[n]` where n = `register_index`. |
| // Returns whether the pop is successful. |
| bool PopRegister(RegisterContext* context, uint8_t register_index) { |
| const uintptr_t sp = RegisterContextStackPointer(context); |
| const uintptr_t stacktop_value = *reinterpret_cast<uintptr_t*>(sp); |
| const auto new_sp = CheckedNumeric<uintptr_t>(sp) + sizeof(uintptr_t); |
| const bool success = |
| new_sp.AssignIfValid(&RegisterContextStackPointer(context)); |
| if (success) |
| *GetRegisterPointer(context, register_index) = stacktop_value; |
| return success; |
| } |
| |
| // Decodes the given bytes as an ULEB128 format number and advances the bytes |
| // pointer by the size of ULEB128. |
| // |
| // This function assumes the given bytes are in valid ULEB128 |
| // format and the decoded number should not overflow `uintptr_t` type. |
| uintptr_t DecodeULEB128(const uint8_t*& bytes) { |
| uintptr_t value = 0; |
| unsigned shift = 0; |
| do { |
| DCHECK_LE(shift, sizeof(uintptr_t) * 8); // ULEB128 must not overflow. |
| value += (*bytes & 0x7fu) << shift; |
| shift += 7; |
| } while (*bytes++ & 0x80); |
| return value; |
| } |
| |
| uint8_t GetTopBits(uint8_t byte, unsigned bits) { |
| DCHECK_LE(bits, 8u); |
| return byte >> (8 - bits); |
| } |
| |
| } // namespace |
| |
| ChromeUnwinderAndroid::ChromeUnwinderAndroid( |
| const ChromeUnwindInfoAndroid& unwind_info, |
| uintptr_t chrome_module_base_address, |
| uintptr_t text_section_start_address) |
| : unwind_info_(unwind_info), |
| chrome_module_base_address_(chrome_module_base_address), |
| text_section_start_address_(text_section_start_address) { |
| DCHECK_GT(text_section_start_address_, chrome_module_base_address_); |
| } |
| |
| bool ChromeUnwinderAndroid::CanUnwindFrom(const Frame& current_frame) const { |
| return current_frame.module && |
| current_frame.module->GetBaseAddress() == chrome_module_base_address_; |
| } |
| |
| UnwindResult ChromeUnwinderAndroid::TryUnwind(RegisterContext* thread_context, |
| uintptr_t stack_top, |
| std::vector<Frame>* stack) { |
| DCHECK(CanUnwindFrom(stack->back())); |
| uintptr_t frame_initial_sp = RegisterContextStackPointer(thread_context); |
| const uintptr_t unwind_initial_pc = |
| RegisterContextInstructionPointer(thread_context); |
| |
| do { |
| const uintptr_t pc = RegisterContextInstructionPointer(thread_context); |
| const uintptr_t instruction_byte_offset_from_text_section_start = |
| pc - text_section_start_address_; |
| |
| const absl::optional<FunctionOffsetTableIndex> function_offset_table_index = |
| GetFunctionTableIndexFromInstructionOffset( |
| unwind_info_.page_table, unwind_info_.function_table, |
| instruction_byte_offset_from_text_section_start); |
| |
| if (!function_offset_table_index) { |
| return UnwindResult::kAborted; |
| } |
| |
| const uint32_t current_unwind_instruction_index = |
| GetFirstUnwindInstructionIndexFromFunctionOffsetTableEntry( |
| &unwind_info_ |
| .function_offset_table[function_offset_table_index |
| ->function_offset_table_byte_index], |
| function_offset_table_index |
| ->instruction_offset_from_function_start); |
| |
| const uint8_t* current_unwind_instruction = |
| &unwind_info_ |
| .unwind_instruction_table[current_unwind_instruction_index]; |
| |
| UnwindInstructionResult instruction_result; |
| bool pc_was_updated = false; |
| |
| do { |
| instruction_result = ExecuteUnwindInstruction( |
| current_unwind_instruction, pc_was_updated, thread_context); |
| const uintptr_t sp = RegisterContextStackPointer(thread_context); |
| if (sp > stack_top || sp < frame_initial_sp || |
| !IsAligned(sp, sizeof(uintptr_t))) { |
| return UnwindResult::kAborted; |
| } |
| } while (instruction_result == |
| UnwindInstructionResult::kInstructionPending); |
| |
| if (instruction_result == UnwindInstructionResult::kAborted) { |
| return UnwindResult::kAborted; |
| } |
| |
| DCHECK_EQ(instruction_result, UnwindInstructionResult::kCompleted); |
| |
| const uintptr_t new_sp = RegisterContextStackPointer(thread_context); |
| // Validate SP is properly aligned across frames. |
| // See |
| // https://community.arm.com/arm-community-blogs/b/architectures-and-processors-blog/posts/using-the-stack-in-aarch32-and-aarch64 |
| // for SP alignment rules. |
| if (!IsAligned(new_sp, 2 * sizeof(uintptr_t))) { |
| return UnwindResult::kAborted; |
| } |
| // Validate that SP does not decrease across frames. |
| const bool is_leaf_frame = stack->size() == 1; |
| // Each frame unwind is expected to only pop from stack memory, which will |
| // cause sp to increase. |
| // Non-Leaf frames are expected to at least pop lr off stack, so sp is |
| // expected to strictly increase for non-leaf frames. |
| if (new_sp <= (is_leaf_frame ? frame_initial_sp - 1 : frame_initial_sp)) { |
| return UnwindResult::kAborted; |
| } |
| |
| // For leaf functions, if SP does not change, PC must change, otherwise, |
| // the overall execution state will be the same before/after the frame |
| // unwind. |
| if (is_leaf_frame && new_sp == frame_initial_sp && |
| RegisterContextInstructionPointer(thread_context) == |
| unwind_initial_pc) { |
| return UnwindResult::kAborted; |
| } |
| |
| frame_initial_sp = new_sp; |
| |
| stack->emplace_back(RegisterContextInstructionPointer(thread_context), |
| module_cache()->GetModuleForAddress( |
| RegisterContextInstructionPointer(thread_context))); |
| } while (CanUnwindFrom(stack->back())); |
| return UnwindResult::kUnrecognizedFrame; |
| } |
| |
| UnwindInstructionResult ExecuteUnwindInstruction( |
| const uint8_t*& instruction, |
| bool& pc_was_updated, |
| RegisterContext* thread_context) { |
| if (GetTopBits(*instruction, 2) == 0b00) { |
| // 00xxxxxx |
| // vsp = vsp + (xxxxxx << 2) + 4. Covers range 0x04-0x100 inclusive. |
| const uintptr_t offset = ((*instruction++ & 0b00111111u) << 2) + 4; |
| |
| const auto new_sp = |
| CheckedNumeric<uintptr_t>(RegisterContextStackPointer(thread_context)) + |
| offset; |
| if (!new_sp.AssignIfValid(&RegisterContextStackPointer(thread_context))) { |
| return UnwindInstructionResult::kAborted; |
| } |
| } else if (GetTopBits(*instruction, 2) == 0b01) { |
| // 01xxxxxx |
| // vsp = vsp - (xxxxxx << 2) - 4. Covers range 0x04-0x100 inclusive. |
| const uintptr_t offset = ((*instruction++ & 0b00111111u) << 2) + 4; |
| const auto new_sp = |
| CheckedNumeric<uintptr_t>(RegisterContextStackPointer(thread_context)) - |
| offset; |
| if (!new_sp.AssignIfValid(&RegisterContextStackPointer(thread_context))) { |
| return UnwindInstructionResult::kAborted; |
| } |
| } else if (GetTopBits(*instruction, 4) == 0b1001) { |
| // 1001nnnn (nnnn != 13,15) |
| // Set vsp = r[nnnn]. |
| const uint8_t register_index = *instruction++ & 0b00001111; |
| DCHECK_NE(register_index, 13); // Must not set sp to sp. |
| DCHECK_NE(register_index, 15); // Must not set sp to pc. |
| // Note: We shouldn't have cases that are setting caller-saved registers |
| // using this instruction. |
| DCHECK_GE(register_index, 4); |
| |
| RegisterContextStackPointer(thread_context) = |
| *GetRegisterPointer(thread_context, register_index); |
| } else if (GetTopBits(*instruction, 5) == 0b10101) { |
| // 10101nnn |
| // Pop r4-r[4+nnn], r14 |
| const uint8_t max_register_index = (*instruction++ & 0b00000111u) + 4; |
| for (uint8_t n = 4; n <= max_register_index; n++) { |
| if (!PopRegister(thread_context, n)) { |
| return UnwindInstructionResult::kAborted; |
| } |
| } |
| if (!PopRegister(thread_context, 14)) { |
| return UnwindInstructionResult::kAborted; |
| } |
| } else if (*instruction == 0b10000000 && *(instruction + 1) == 0) { |
| // 10000000 00000000 |
| // Refuse to unwind. |
| instruction += 2; |
| return UnwindInstructionResult::kAborted; |
| } else if (GetTopBits(*instruction, 4) == 0b1000) { |
| const uint32_t register_bitmask = |
| ((*instruction & 0xfu) << 8) + *(instruction + 1); |
| instruction += 2; |
| // 1000iiii iiiiiiii |
| // Pop up to 12 integer registers under masks {r15-r12}, {r11-r4} |
| for (uint8_t register_index = 4; register_index < 16; register_index++) { |
| if (register_bitmask & (1 << (register_index - 4))) { |
| if (!PopRegister(thread_context, register_index)) { |
| return UnwindInstructionResult::kAborted; |
| } |
| } |
| } |
| // If we set pc (r15) with value on stack, we should no longer copy lr to |
| // pc on COMPLETE. |
| pc_was_updated |= register_bitmask & (1 << (15 - 4)); |
| } else if (*instruction == 0b10110000) { |
| // Finish |
| // Code 0xb0, Finish, copies VRS[r14] to VRS[r15] and also |
| // indicates that no further instructions are to be processed for this |
| // frame. |
| |
| instruction++; |
| // Only copy lr to pc when pc is not updated by other instructions before. |
| if (!pc_was_updated) |
| thread_context->arm_pc = thread_context->arm_lr; |
| |
| return UnwindInstructionResult::kCompleted; |
| } else if (*instruction == 0b10110010) { |
| // 10110010 uleb128 |
| // vsp = vsp + 0x204 + (uleb128 << 2) |
| // (for vsp increments of 0x104-0x200, use 00xxxxxx twice) |
| instruction++; |
| const auto new_sp = |
| CheckedNumeric<uintptr_t>(RegisterContextStackPointer(thread_context)) + |
| (CheckedNumeric<uintptr_t>(DecodeULEB128(instruction)) << 2) + 0x204; |
| |
| if (!new_sp.AssignIfValid(&RegisterContextStackPointer(thread_context))) { |
| return UnwindInstructionResult::kAborted; |
| } |
| } else { |
| NOTREACHED(); |
| } |
| return UnwindInstructionResult::kInstructionPending; |
| } |
| |
| uintptr_t GetFirstUnwindInstructionIndexFromFunctionOffsetTableEntry( |
| const uint8_t* function_offset_table_entry, |
| int instruction_offset_from_function_start) { |
| DCHECK_GE(instruction_offset_from_function_start, 0); |
| const uint8_t* current_function_offset_table_position = |
| function_offset_table_entry; |
| |
| do { |
| const uintptr_t function_offset = |
| DecodeULEB128(current_function_offset_table_position); |
| |
| const uintptr_t unwind_table_index = |
| DecodeULEB128(current_function_offset_table_position); |
| |
| // Each function always ends at 0 offset. It is guaranteed to find an entry |
| // as long as the function offset table is well-structured. |
| if (function_offset <= |
| static_cast<uint32_t>(instruction_offset_from_function_start)) |
| return unwind_table_index; |
| |
| } while (true); |
| |
| NOTREACHED(); |
| return 0; |
| } |
| |
| const absl::optional<FunctionOffsetTableIndex> |
| GetFunctionTableIndexFromInstructionOffset( |
| span<const uint32_t> page_start_instructions, |
| span<const FunctionTableEntry> function_offset_table_indices, |
| uint32_t instruction_byte_offset_from_text_section_start) { |
| DCHECK(!page_start_instructions.empty()); |
| DCHECK(!function_offset_table_indices.empty()); |
| // First function on first page should always start from 0 offset. |
| DCHECK_EQ(function_offset_table_indices.front() |
| .function_start_address_page_instruction_offset, |
| 0ul); |
| |
| const uint16_t page_number = |
| instruction_byte_offset_from_text_section_start >> 17; |
| const uint16_t page_instruction_offset = |
| (instruction_byte_offset_from_text_section_start >> 1) & |
| 0xffff; // 16 bits. |
| |
| // Invalid instruction_byte_offset_from_text_section_start: |
| // instruction_byte_offset_from_text_section_start falls after the last page. |
| if (page_number >= page_start_instructions.size()) { |
| return absl::nullopt; |
| } |
| |
| const span<const FunctionTableEntry>::const_iterator |
| function_table_entry_start = |
| function_offset_table_indices.begin() + |
| checked_cast<ptrdiff_t>(page_start_instructions[page_number]); |
| const span<const FunctionTableEntry>::const_iterator |
| function_table_entry_end = |
| page_number == page_start_instructions.size() - 1 |
| ? function_offset_table_indices.end() |
| : function_offset_table_indices.begin() + |
| checked_cast<ptrdiff_t>( |
| page_start_instructions[page_number + 1]); |
| |
| // `std::upper_bound` finds first element that > target in range |
| // [function_table_entry_start, function_table_entry_end). |
| const auto first_larger_entry_location = std::upper_bound( |
| function_table_entry_start, function_table_entry_end, |
| page_instruction_offset, |
| [](uint16_t page_instruction_offset, const FunctionTableEntry& entry) { |
| return page_instruction_offset < |
| entry.function_start_address_page_instruction_offset; |
| }); |
| |
| // Offsets the element found by 1 to get the biggest element that <= target. |
| const auto entry_location = first_larger_entry_location - 1; |
| |
| // When all offsets in current range > page_instruction_offset (including when |
| // there is no entry in current range), the `FunctionTableEntry` we are |
| // looking for is not within the function_offset_table_indices range we are |
| // inspecting, because the function is too long that it spans multiple pages. |
| // |
| // We need to locate the previous entry on function_offset_table_indices and |
| // find its corresponding page_table index. |
| // |
| // Example: |
| // +--------------------+--------------------+ |
| // | <-----2 byte-----> | <-----2 byte-----> | |
| // +--------------------+--------------------+ |
| // | Page Offset | Offset Table Index | |
| // +--------------------+--------------------+----- |
| // | 10 | XXX | | |
| // +--------------------+--------------------+ | |
| // | ... | ... |Page 0x100 |
| // +--------------------+--------------------+ | |
| // | 65500 | ZZZ | | |
| // +--------------------+--------------------+----- Page 0x101 is empty |
| // | 200 | AAA | | |
| // +--------------------+--------------------+ | |
| // | ... | ... |Page 0x102 |
| // +--------------------+--------------------+ | |
| // | 65535 | BBB | | |
| // +--------------------+--------------------+----- |
| // |
| // Example: |
| // For |
| // - page_number = 0x100, page_instruction_offset >= 65535 |
| // - page_number = 0x101, all page_instruction_offset |
| // - page_number = 0x102, page_instruction_offset < 200 |
| // We should be able to map them all to entry [65500, ZZZ] in page 0x100. |
| |
| // Finds the page_number that corresponds to `entry_location`. The page |
| // might not be the page we are inspecting, when the function spans over |
| // multiple pages. |
| uint16_t function_start_page_number = page_number; |
| while (function_offset_table_indices.begin() + |
| checked_cast<ptrdiff_t>( |
| page_start_instructions[function_start_page_number]) > |
| entry_location) { |
| // First page in page table must not be empty. |
| DCHECK_NE(function_start_page_number, 0); |
| function_start_page_number--; |
| }; |
| |
| const uint32_t function_start_address_instruction_offset = |
| (uint32_t{function_start_page_number} << 16) + |
| entry_location->function_start_address_page_instruction_offset; |
| |
| const int instruction_offset_from_function_start = |
| static_cast<int>((instruction_byte_offset_from_text_section_start >> 1) - |
| function_start_address_instruction_offset); |
| |
| DCHECK_GE(instruction_offset_from_function_start, 0); |
| return FunctionOffsetTableIndex{ |
| instruction_offset_from_function_start, |
| entry_location->function_offset_table_byte_index, |
| }; |
| } |
| |
| } // namespace base |
