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Diffstat (limited to 'libcorkscrew/arch-arm/backtrace-arm.c')
| -rw-r--r-- | libcorkscrew/arch-arm/backtrace-arm.c | 589 |
1 files changed, 589 insertions, 0 deletions
diff --git a/libcorkscrew/arch-arm/backtrace-arm.c b/libcorkscrew/arch-arm/backtrace-arm.c new file mode 100644 index 0000000..5b91164 --- /dev/null +++ b/libcorkscrew/arch-arm/backtrace-arm.c @@ -0,0 +1,589 @@ +/* + * Copyright (C) 2011 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. + */ + +/* + * Backtracing functions for ARM. + * + * This implementation uses the exception unwinding tables provided by + * the compiler to unwind call frames. Refer to the ARM Exception Handling ABI + * documentation (EHABI) for more details about what's going on here. + * + * An ELF binary may contain an EXIDX section that provides an index to + * the exception handling table of each function, sorted by program + * counter address. + * + * This implementation also supports unwinding other processes via ptrace(). + * In that case, the EXIDX section is found by reading the ELF section table + * structures using ptrace(). + * + * Because the tables are used for exception handling, it can happen that + * a given function will not have an exception handling table. In particular, + * exceptions are assumed to only ever be thrown at call sites. Therefore, + * by definition leaf functions will not have exception handling tables. + * This may make unwinding impossible in some cases although we can still get + * some idea of the call stack by examining the PC and LR registers. + * + * As we are only interested in backtrace information, we do not need + * to perform all of the work of unwinding such as restoring register + * state and running cleanup functions. Unwinding is performed virtually on + * an abstract machine context consisting of just the ARM core registers. + * Furthermore, we do not run generic "personality functions" because + * we may not be in a position to execute arbitrary code, especially if + * we are running in a signal handler or using ptrace()! + */ + +#define LOG_TAG "Corkscrew" +//#define LOG_NDEBUG 0 + +#include "../backtrace-arch.h" +#include "../backtrace-helper.h" +#include "../ptrace-arch.h" +#include <corkscrew/ptrace.h> + +#include <stdlib.h> +#include <signal.h> +#include <stdbool.h> +#include <limits.h> +#include <errno.h> +#include <sys/ptrace.h> +#include <sys/exec_elf.h> +#include <cutils/log.h> + +/* Machine context at the time a signal was raised. */ +typedef struct ucontext { + uint32_t uc_flags; + struct ucontext* uc_link; + stack_t uc_stack; + struct sigcontext { + uint32_t trap_no; + uint32_t error_code; + uint32_t oldmask; + uint32_t gregs[16]; + uint32_t arm_cpsr; + uint32_t fault_address; + } uc_mcontext; + uint32_t uc_sigmask; +} ucontext_t; + +/* Unwind state. */ +typedef struct { + uint32_t gregs[16]; +} unwind_state_t; + +static const int R_SP = 13; +static const int R_LR = 14; +static const int R_PC = 15; + +/* Special EXIDX value that indicates that a frame cannot be unwound. */ +static const uint32_t EXIDX_CANTUNWIND = 1; + +/* Get the EXIDX section start and size for the module that contains a + * given program counter address. + * + * When the executable is statically linked, the EXIDX section can be + * accessed by querying the values of the __exidx_start and __exidx_end + * symbols. + * + * When the executable is dynamically linked, the linker exports a function + * called dl_unwind_find_exidx that obtains the EXIDX section for a given + * absolute program counter address. + * + * Bionic exports a helpful function called __gnu_Unwind_Find_exidx that + * handles both cases, so we use that here. + */ +typedef long unsigned int* _Unwind_Ptr; +extern _Unwind_Ptr __gnu_Unwind_Find_exidx(_Unwind_Ptr pc, int *pcount); + +static uintptr_t find_exidx(uintptr_t pc, size_t* out_exidx_size) { + int count; + uintptr_t start = (uintptr_t)__gnu_Unwind_Find_exidx((_Unwind_Ptr)pc, &count); + *out_exidx_size = count; + return start; +} + +/* Transforms a 31-bit place-relative offset to an absolute address. + * We assume the most significant bit is clear. */ +static uintptr_t prel_to_absolute(uintptr_t place, uint32_t prel_offset) { + return place + (((int32_t)(prel_offset << 1)) >> 1); +} + +static uintptr_t get_exception_handler(const memory_t* memory, + const map_info_t* map_info_list, uintptr_t pc) { + if (!pc) { + ALOGV("get_exception_handler: pc is zero, no handler"); + return 0; + } + + uintptr_t exidx_start; + size_t exidx_size; + const map_info_t* mi; + if (memory->tid < 0) { + mi = NULL; + exidx_start = find_exidx(pc, &exidx_size); + } else { + mi = find_map_info(map_info_list, pc); + if (mi && mi->data) { + const map_info_data_t* data = (const map_info_data_t*)mi->data; + exidx_start = data->exidx_start; + exidx_size = data->exidx_size; + } else { + exidx_start = 0; + exidx_size = 0; + } + } + + uintptr_t handler = 0; + int32_t handler_index = -1; + if (exidx_start) { + uint32_t low = 0; + uint32_t high = exidx_size; + while (low < high) { + uint32_t index = (low + high) / 2; + uintptr_t entry = exidx_start + index * 8; + uint32_t entry_prel_pc; + ALOGV("XXX low=%u, high=%u, index=%u", low, high, index); + if (!try_get_word(memory, entry, &entry_prel_pc)) { + break; + } + uintptr_t entry_pc = prel_to_absolute(entry, entry_prel_pc); + ALOGV("XXX entry_pc=0x%08x", entry_pc); + if (pc < entry_pc) { + high = index; + continue; + } + if (index + 1 < exidx_size) { + uintptr_t next_entry = entry + 8; + uint32_t next_entry_prel_pc; + if (!try_get_word(memory, next_entry, &next_entry_prel_pc)) { + break; + } + uintptr_t next_entry_pc = prel_to_absolute(next_entry, next_entry_prel_pc); + ALOGV("XXX next_entry_pc=0x%08x", next_entry_pc); + if (pc >= next_entry_pc) { + low = index + 1; + continue; + } + } + + uintptr_t entry_handler_ptr = entry + 4; + uint32_t entry_handler; + if (!try_get_word(memory, entry_handler_ptr, &entry_handler)) { + break; + } + if (entry_handler & (1L << 31)) { + handler = entry_handler_ptr; // in-place handler data + } else if (entry_handler != EXIDX_CANTUNWIND) { + handler = prel_to_absolute(entry_handler_ptr, entry_handler); + } + handler_index = index; + break; + } + } + if (mi) { + ALOGV("get_exception_handler: pc=0x%08x, module='%s', module_start=0x%08x, " + "exidx_start=0x%08x, exidx_size=%d, handler=0x%08x, handler_index=%d", + pc, mi->name, mi->start, exidx_start, exidx_size, handler, handler_index); + } else { + ALOGV("get_exception_handler: pc=0x%08x, " + "exidx_start=0x%08x, exidx_size=%d, handler=0x%08x, handler_index=%d", + pc, exidx_start, exidx_size, handler, handler_index); + } + return handler; +} + +typedef struct { + uintptr_t ptr; + uint32_t word; +} byte_stream_t; + +static bool try_next_byte(const memory_t* memory, byte_stream_t* stream, uint8_t* out_value) { + uint8_t result; + switch (stream->ptr & 3) { + case 0: + if (!try_get_word(memory, stream->ptr, &stream->word)) { + *out_value = 0; + return false; + } + *out_value = stream->word >> 24; + break; + + case 1: + *out_value = stream->word >> 16; + break; + + case 2: + *out_value = stream->word >> 8; + break; + + default: + *out_value = stream->word; + break; + } + + ALOGV("next_byte: ptr=0x%08x, value=0x%02x", stream->ptr, *out_value); + stream->ptr += 1; + return true; +} + +static void set_reg(unwind_state_t* state, uint32_t reg, uint32_t value) { + ALOGV("set_reg: reg=%d, value=0x%08x", reg, value); + state->gregs[reg] = value; +} + +static bool try_pop_registers(const memory_t* memory, unwind_state_t* state, uint32_t mask) { + uint32_t sp = state->gregs[R_SP]; + bool sp_updated = false; + for (int i = 0; i < 16; i++) { + if (mask & (1 << i)) { + uint32_t value; + if (!try_get_word(memory, sp, &value)) { + return false; + } + if (i == R_SP) { + sp_updated = true; + } + set_reg(state, i, value); + sp += 4; + } + } + if (!sp_updated) { + set_reg(state, R_SP, sp); + } + return true; +} + +/* Executes a built-in personality routine as defined in the EHABI. + * Returns true if unwinding should continue. + * + * The data for the built-in personality routines consists of a sequence + * of unwinding instructions, followed by a sequence of scope descriptors, + * each of which has a length and offset encoded using 16-bit or 32-bit + * values. + * + * We only care about the unwinding instructions. They specify the + * operations of an abstract machine whose purpose is to transform the + * virtual register state (including the stack pointer) such that + * the call frame is unwound and the PC register points to the call site. + */ +static bool execute_personality_routine(const memory_t* memory, + unwind_state_t* state, byte_stream_t* stream, int pr_index) { + size_t size; + switch (pr_index) { + case 0: // Personality routine #0, short frame, descriptors have 16-bit scope. + size = 3; + break; + case 1: // Personality routine #1, long frame, descriptors have 16-bit scope. + case 2: { // Personality routine #2, long frame, descriptors have 32-bit scope. + uint8_t size_byte; + if (!try_next_byte(memory, stream, &size_byte)) { + return false; + } + size = (uint32_t)size_byte * sizeof(uint32_t) + 2; + break; + } + default: // Unknown personality routine. Stop here. + return false; + } + + bool pc_was_set = false; + while (size--) { + uint8_t op; + if (!try_next_byte(memory, stream, &op)) { + return false; + } + if ((op & 0xc0) == 0x00) { + // "vsp = vsp + (xxxxxx << 2) + 4" + set_reg(state, R_SP, state->gregs[R_SP] + ((op & 0x3f) << 2) + 4); + } else if ((op & 0xc0) == 0x40) { + // "vsp = vsp - (xxxxxx << 2) - 4" + set_reg(state, R_SP, state->gregs[R_SP] - ((op & 0x3f) << 2) - 4); + } else if ((op & 0xf0) == 0x80) { + uint8_t op2; + if (!(size--) || !try_next_byte(memory, stream, &op2)) { + return false; + } + uint32_t mask = (((uint32_t)op & 0x0f) << 12) | ((uint32_t)op2 << 4); + if (mask) { + // "Pop up to 12 integer registers under masks {r15-r12}, {r11-r4}" + if (!try_pop_registers(memory, state, mask)) { + return false; + } + if (mask & (1 << R_PC)) { + pc_was_set = true; + } + } else { + // "Refuse to unwind" + return false; + } + } else if ((op & 0xf0) == 0x90) { + if (op != 0x9d && op != 0x9f) { + // "Set vsp = r[nnnn]" + set_reg(state, R_SP, state->gregs[op & 0x0f]); + } else { + // "Reserved as prefix for ARM register to register moves" + // "Reserved as prefix for Intel Wireless MMX register to register moves" + return false; + } + } else if ((op & 0xf8) == 0xa0) { + // "Pop r4-r[4+nnn]" + uint32_t mask = (0x0ff0 >> (7 - (op & 0x07))) & 0x0ff0; + if (!try_pop_registers(memory, state, mask)) { + return false; + } + } else if ((op & 0xf8) == 0xa8) { + // "Pop r4-r[4+nnn], r14" + uint32_t mask = ((0x0ff0 >> (7 - (op & 0x07))) & 0x0ff0) | 0x4000; + if (!try_pop_registers(memory, state, mask)) { + return false; + } + } else if (op == 0xb0) { + // "Finish" + break; + } else if (op == 0xb1) { + uint8_t op2; + if (!(size--) || !try_next_byte(memory, stream, &op2)) { + return false; + } + if (op2 != 0x00 && (op2 & 0xf0) == 0x00) { + // "Pop integer registers under mask {r3, r2, r1, r0}" + if (!try_pop_registers(memory, state, op2)) { + return false; + } + } else { + // "Spare" + return false; + } + } else if (op == 0xb2) { + // "vsp = vsp + 0x204 + (uleb128 << 2)" + uint32_t value = 0; + uint32_t shift = 0; + uint8_t op2; + do { + if (!(size--) || !try_next_byte(memory, stream, &op2)) { + return false; + } + value |= (op2 & 0x7f) << shift; + shift += 7; + } while (op2 & 0x80); + set_reg(state, R_SP, state->gregs[R_SP] + (value << 2) + 0x204); + } else if (op == 0xb3) { + // "Pop VFP double-precision registers D[ssss]-D[ssss+cccc] saved (as if) by FSTMFDX" + uint8_t op2; + if (!(size--) || !try_next_byte(memory, stream, &op2)) { + return false; + } + set_reg(state, R_SP, state->gregs[R_SP] + (uint32_t)(op2 & 0x0f) * 8 + 12); + } else if ((op & 0xf8) == 0xb8) { + // "Pop VFP double-precision registers D[8]-D[8+nnn] saved (as if) by FSTMFDX" + set_reg(state, R_SP, state->gregs[R_SP] + (uint32_t)(op & 0x07) * 8 + 12); + } else if ((op & 0xf8) == 0xc0) { + // "Intel Wireless MMX pop wR[10]-wR[10+nnn]" + set_reg(state, R_SP, state->gregs[R_SP] + (uint32_t)(op & 0x07) * 8 + 8); + } else if (op == 0xc6) { + // "Intel Wireless MMX pop wR[ssss]-wR[ssss+cccc]" + uint8_t op2; + if (!(size--) || !try_next_byte(memory, stream, &op2)) { + return false; + } + set_reg(state, R_SP, state->gregs[R_SP] + (uint32_t)(op2 & 0x0f) * 8 + 8); + } else if (op == 0xc7) { + uint8_t op2; + if (!(size--) || !try_next_byte(memory, stream, &op2)) { + return false; + } + if (op2 != 0x00 && (op2 & 0xf0) == 0x00) { + // "Intel Wireless MMX pop wCGR registers under mask {wCGR3,2,1,0}" + set_reg(state, R_SP, state->gregs[R_SP] + __builtin_popcount(op2) * 4); + } else { + // "Spare" + return false; + } + } else if (op == 0xc8) { + // "Pop VFP double precision registers D[16+ssss]-D[16+ssss+cccc] + // saved (as if) by FSTMFD" + uint8_t op2; + if (!(size--) || !try_next_byte(memory, stream, &op2)) { + return false; + } + set_reg(state, R_SP, state->gregs[R_SP] + (uint32_t)(op2 & 0x0f) * 8 + 8); + } else if (op == 0xc9) { + // "Pop VFP double precision registers D[ssss]-D[ssss+cccc] saved (as if) by FSTMFDD" + uint8_t op2; + if (!(size--) || !try_next_byte(memory, stream, &op2)) { + return false; + } + set_reg(state, R_SP, state->gregs[R_SP] + (uint32_t)(op2 & 0x0f) * 8 + 8); + } else if ((op == 0xf8) == 0xd0) { + // "Pop VFP double-precision registers D[8]-D[8+nnn] saved (as if) by FSTMFDD" + set_reg(state, R_SP, state->gregs[R_SP] + (uint32_t)(op & 0x07) * 8 + 8); + } else { + // "Spare" + return false; + } + } + if (!pc_was_set) { + set_reg(state, R_PC, state->gregs[R_LR]); + } + return true; +} + +static bool try_get_half_word(const memory_t* memory, uint32_t pc, uint16_t* out_value) { + uint32_t word; + if (try_get_word(memory, pc & ~2, &word)) { + *out_value = pc & 2 ? word >> 16 : word & 0xffff; + return true; + } + return false; +} + +uintptr_t rewind_pc_arch(const memory_t* memory, uintptr_t pc) { + if (pc & 1) { + /* Thumb mode - need to check whether the bl(x) has long offset or not. + * Examples: + * + * arm blx in the middle of thumb: + * 187ae: 2300 movs r3, #0 + * 187b0: f7fe ee1c blx 173ec + * 187b4: 2c00 cmp r4, #0 + * + * arm bl in the middle of thumb: + * 187d8: 1c20 adds r0, r4, #0 + * 187da: f136 fd15 bl 14f208 + * 187de: 2800 cmp r0, #0 + * + * pure thumb: + * 18894: 189b adds r3, r3, r2 + * 18896: 4798 blx r3 + * 18898: b001 add sp, #4 + */ + uint16_t prev1, prev2; + if (try_get_half_word(memory, pc - 5, &prev1) + && ((prev1 & 0xf000) == 0xf000) + && try_get_half_word(memory, pc - 3, &prev2) + && ((prev2 & 0xe000) == 0xe000)) { + pc -= 4; // long offset + } else { + pc -= 2; + } + } else { + /* ARM mode, all instructions are 32bit. Yay! */ + pc -= 4; + } + return pc; +} + +static ssize_t unwind_backtrace_common(const memory_t* memory, + const map_info_t* map_info_list, + unwind_state_t* state, backtrace_frame_t* backtrace, + size_t ignore_depth, size_t max_depth) { + size_t ignored_frames = 0; + size_t returned_frames = 0; + + for (size_t index = 0; returned_frames < max_depth; index++) { + uintptr_t pc = index ? rewind_pc_arch(memory, state->gregs[R_PC]) + : state->gregs[R_PC]; + backtrace_frame_t* frame = add_backtrace_entry(pc, + backtrace, ignore_depth, max_depth, &ignored_frames, &returned_frames); + if (frame) { + frame->stack_top = state->gregs[R_SP]; + } + + uintptr_t handler = get_exception_handler(memory, map_info_list, pc); + if (!handler) { + // If there is no handler for the PC and this is the first frame, + // then the program may have branched to an invalid address. + // Try starting from the LR instead, otherwise stop unwinding. + if (index == 0 && state->gregs[R_LR] + && state->gregs[R_LR] != state->gregs[R_PC]) { + set_reg(state, R_PC, state->gregs[R_LR]); + continue; + } else { + break; + } + } + + byte_stream_t stream; + stream.ptr = handler; + uint8_t pr; + if (!try_next_byte(memory, &stream, &pr)) { + break; + } + if ((pr & 0xf0) != 0x80) { + // The first word is a place-relative pointer to a generic personality + // routine function. We don't support invoking such functions, so stop here. + break; + } + + // The first byte indicates the personality routine to execute. + // Following bytes provide instructions to the personality routine. + if (!execute_personality_routine(memory, state, &stream, pr & 0x0f)) { + break; + } + if (frame && state->gregs[R_SP] > frame->stack_top) { + frame->stack_size = state->gregs[R_SP] - frame->stack_top; + } + if (!state->gregs[R_PC]) { + break; + } + } + + // Ran out of frames that we could unwind using handlers. + // Add a final entry for the LR if it looks sane and call it good. + if (returned_frames < max_depth + && state->gregs[R_LR] + && state->gregs[R_LR] != state->gregs[R_PC] + && is_executable_map(map_info_list, state->gregs[R_LR])) { + // We don't know where the stack for this extra frame starts so we + // don't return any stack information for it. + add_backtrace_entry(rewind_pc_arch(memory, state->gregs[R_LR]), + backtrace, ignore_depth, max_depth, &ignored_frames, &returned_frames); + } + return returned_frames; +} + +ssize_t unwind_backtrace_signal_arch(siginfo_t* siginfo, void* sigcontext, + const map_info_t* map_info_list, + backtrace_frame_t* backtrace, size_t ignore_depth, size_t max_depth) { + const ucontext_t* uc = (const ucontext_t*)sigcontext; + + unwind_state_t state; + for (int i = 0; i < 16; i++) { + state.gregs[i] = uc->uc_mcontext.gregs[i]; + } + + memory_t memory; + init_memory(&memory, map_info_list); + return unwind_backtrace_common(&memory, map_info_list, &state, + backtrace, ignore_depth, max_depth); +} + +ssize_t unwind_backtrace_ptrace_arch(pid_t tid, const ptrace_context_t* context, + backtrace_frame_t* backtrace, size_t ignore_depth, size_t max_depth) { + struct pt_regs regs; + if (ptrace(PTRACE_GETREGS, tid, 0, ®s)) { + return -1; + } + + unwind_state_t state; + for (int i = 0; i < 16; i++) { + state.gregs[i] = regs.uregs[i]; + } + + memory_t memory; + init_memory_ptrace(&memory, tid); + return unwind_backtrace_common(&memory, context->map_info_list, &state, + backtrace, ignore_depth, max_depth); +} |