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esp-idf/components/esp_system/eh_frame_parser.c

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/*
* SPDX-FileCopyrightText: 2020-2022 Espressif Systems (Shanghai) CO LTD
*
* SPDX-License-Identifier: Apache-2.0
*/
/**
* @file DWARF Exception Frames parser
*
* This file performs parsing and execution of DWARF except frames described in
* section `.eh_frame` and `.eh_frame_hdr`. This is currently used on RISC-V
* boards to implement a complete backtracing when a panic occurs.
*
* More information about the sections structure and DWARF instructions can be
* found in the official documentation:
* http://dwarfstd.org/Download.php
*/
#include "esp_private/eh_frame_parser.h"
#include "esp_private/panic_internal.h"
#include <string.h>
#if CONFIG_ESP_SYSTEM_USE_EH_FRAME
#include "eh_frame_parser_impl.h"
/**
* @brief Dimension of an array (number of elements)
*/
#ifndef DIM
#define DIM(array) (sizeof(array)/sizeof(*array))
#endif
/**
* @brief DWARF Exception Header Encoding
* This is used to know how the data in .eh_frame and .eh_frame_hdr sections
* are encoded.
*/
/* DWARF Exception Exception Header value format. */
#define DW_EH_PE_omit 0xff /*!< No value is present */
#define DW_EH_PE_uleb128 0x01 /*!< Unsigned value encoded in LEB128 (Little Endian Base 128). */
#define DW_EH_PE_udata2 0x02 /*!< Unsigned 16-bit value. */
#define DW_EH_PE_udata4 0x03 /*!< Unsigned 32-bit value. */
#define DW_EH_PE_udata8 0x04 /*!< Unsigned 64-bit value. */
#define DW_EH_PE_sleb128 0x09 /*!< Signed value encoded in LEB128 (Little Endian Base 128). */
#define DW_EH_PE_sdata2 0x0A /*!< Signed 16-bit value. */
#define DW_EH_PE_sdata4 0x0B /*!< Signed 32-bit value. */
#define DW_EH_PE_sdata8 0x0C /*!< Signed 64-bit value. */
/* DWARF Exception Exception Header value application.
* These values are in fact represented in the high nibble of a given data.
* For example:
* 0x3A describes the values as signed 16-bit offsets relative to .eh_frame_hdr section.
* 0x11 describes the values as unsigned value encoded in LEB128, relative to their location ion memory. */
#define DW_EH_PE_absptr 0x00 /*!< The value itself is a pointer, it is not an offset. */
#define DW_EH_PE_pcrel 0x01 /*!< The value is an offset, relative to its location in memory. */
#define DW_EH_PE_datarel 0x03 /*!< The value is an offset, relative to .eh_frame_hdr section. */
/* Macros simplifying testing relative offset data encoding. */
#define ESP_ENCODING_PC_REL(ENCODING) (((ENCODING >> 4) & 0xf) == DW_EH_PE_pcrel)
#define ESP_ENCODING_FRAME_HDR_REL(ENCODING) (((ENCODING >> 4) & 0xf) == DW_EH_PE_datarel)
/**
* @brief Call Frame Information (CIE) fields information.
* As the size of CIE is variable, the simplest way to described it is to
* have a pointer at the beginning of CIE structure and access the fields
* thanks to the index macros defined here.
*/
#define ESP_CIE_VARIABLE_FIELDS_IDX (9) /*!< Offset, in bytes, where variable length fields start. */
/**
* @brief Frame Description Entry (FDE) fields index.
* For the same reasons as above, we prefer defining these macros rather than
* having a structure.
*/
#define ESP_FDE_LENGTH_IDX (0) /*!< Length, in bytes, of the FDE excluding this field. 4 bytes field. */
#define ESP_FDE_CIE_IDX (1) /*!< Nearest preceding Common Information Entry (CIE) offset. 4 bytes field. */
#define ESP_FDE_INITLOC_IDX (2) /*!< Initial location (of the function) the FDE describes. Variable size (encoding in CIE). */
#define ESP_FDE_RANGELEN_IDX (3) /*!< Size, in bytes, of the function described by this FDE location the FDE describes. Variable size (encoding in CIE). */
#define ESP_FDE_AUGMENTATION_IDX (4) /*!< Augmentation data length. Unsigned LEB128. */
/**
* @brief Pointers to both .eh_frame_hdr and .eh_frame sections.
*/
#define EH_FRAME_HDR_ADDR (&__eh_frame_hdr)
#define EH_FRAME_ADDR (&__eh_frame)
/**
* @brief Structure of .eh_frame_hdr section header.
*/
typedef struct {
uint8_t version; /*!< Structure version, must be 1.*/
uint8_t eh_frame_ptr_enc; /*!< eh_frame_ptr entry encoding. */
uint8_t fde_count_enc; /*!< fde_count entry encoding. */
uint8_t table_enc; /*!< table entries encoding. */
/* The rest of the structure has variable length. Thus, we cannot define
* them here. Here are their names:
* - eh_frame_ptr : encoded pointer to the .eh_frame section.
* - fde_Count : number of entries in the array of table_entry.
* - table_entry array : sorted array of table_entry. */
} __attribute__((packed)) fde_header;
/**
* @brief .eh_frame_hdr table's entry format.
* Each entry of the table contains 2 32-bit encoded addresses.
* Encoding is defined in the previous structure. Check table_enc field.
*/
typedef struct {
uint32_t fun_addr; /*!< Address of the function described. */
uint32_t fde_addr; /*!< Address of the FDE for the function.*/
} table_entry;
/**
* @brief DWARF state constant macros.
*/
#define ESP_EH_FRAME_STACK_SIZE (2) /*!< DWARF virtual machine can save the push the current on a virtual
stack. we mimic the stack with an array. While testing, a stack
size of 2 was enough. */
/**
* @brief
* Structure representing the state of the DWARF virtual machine.
*/
typedef struct {
/* Stack for DWARF state registers.
* For caller saved registers, save their CFA address (value in previous call frame).
* As these registers will be used to define offset in the CFA, they will always be
* multiple of CPU word (4-bytes in our case). Thus, it will save the offset in word-size, not
* in bytes. Plus, the highest bit will be used to mark that this register is NOY
* ESP_EH_FRAME_REG_SAME. (0x80000000 is a valid value then, meaning that the register value
* is CFA + 0 offset) */
uint32_t regs_offset[ESP_EH_FRAME_STACK_SIZE][EXECUTION_FRAME_MAX_REGS];
/* reg_offset represents the state of registers when PC reaches the following location. */
uint32_t location;
/* Index of the registers offset to use (1 for saved offset, 0 else). */
uint8_t offset_idx;
} dwarf_regs;
/**
* @brief DWARF's register state.
* When a DWARF register is set to ESP_EH_FRAME_REG_SAME, the CPU register corresponding to this
* virtual register will be unchanged after executing DWARF instructions.
* Please see esp_eh_frame_restore_caller_state() for more details.
*/
#define ESP_EH_FRAME_REG_SAME (0)
/**
* @brief Set a register's offset (relative to CFA).
* The highest bit is set to 1 to mark that this register needs to be retrived because it has been
* altered.
*/
#define ESP_EH_FRAME_SET_REG_OFFSET(offset) (0x80000000 | offset)
/**
* @brief Get a register's offset (relative to CFA).
*/
#define ESP_EH_FRAME_GET_REG_OFFSET(offset) (0x7fffffff & offset)
/**
* @brief Get a register's CFA offset.
*/
#define ESP_EH_FRAME_IS_CFA_RELATIVE(reg) ((reg >> 31) == 1)
/**
* @brief Test whether an offset is small enough to be stored
* in our 32-bit register.
* Note: the highest bit is used.
*/
#define ESP_EH_FRAME_CFA_OFFSET_VALID(offset) (offset < 0x80000000)
/**
* @brief Index of Call Frame Address (CFA) in DWARF registers array.
*/
#define ESP_ESH_FRAME_CFA_IDX (EXECUTION_FRAME_SP_REG)
/**
* @brief Macros to get and set CFA's relative register and offset.
* Indeed, CFA is defined by two values: register and offset. CFA is then
* calculated by adding the offset to the register value.
* `register` will be stored in the lowest 8 bits.
* `offset` will be stored in the highest 24 bits.
*
* NOTE: with this implementation, CFA will be affected by
* DW_CFA_REMEMBER_STATE and DW_CFA_RESTORE_STATE instructions.
*/
#if EXECUTION_FRAME_MAX_REGS > 255
#error "Too many registers defined for the target ExecutionFrame"
#endif
#define ESP_EH_FRAME_CFA_REG_VALID(reg) (reg < EXECUTION_FRAME_MAX_REGS)
#define ESP_EH_FRAME_CFA_OFF_VALID(off) (((off) >> 24) == 0)
#define ESP_EH_FRAME_CFA(state) ((state)->regs_offset[(state)->offset_idx][ESP_ESH_FRAME_CFA_IDX])
#define ESP_EH_FRAME_NEW_CFA(reg, off) (((off) << 8) | ((reg) & 0xff))
#define ESP_EH_FRAME_SET_CFA_REG(value, reg) (((value) & ~0xff) | ((reg) & 0xff))
#define ESP_EH_FRAME_SET_CFA_OFF(value, off) (((value) & 0xff) | ((off) << 8))
#define ESP_EH_FRAME_GET_CFA_REG(value) ((value) & 0xff)
#define ESP_EH_FRAME_GET_CFA_OFF(value) ((value) >> 8)
/**
* @brief Unsupported opcode value to return when exeucting 0-opcode type instructions.
*/
#define ESP_EH_FRAME_UNSUPPORTED_OPCODE ((uint32_t) -1)
/**
* @brief Macros defining the DWARF instructions code.
*/
#define DW_GET_OPCODE(OP) ((OP) >> 6)
#define DW_GET_PARAM(OP) ((OP) & 0b111111)
#define DW_CFA_ADVANCE_LOC (1)
#define DW_CFA_OFFSET (2)
#define DW_CFA_RESTORE (3)
/**
* @brief Constant for DWARF instructions code when high 2 bits are 0.
*/
#define DW_CFA_0_OPCODE (0)
#define DW_CFA_NOP (0x0)
#define DW_CFA_SET_LOC (0x1)
#define DW_CFA_ADVANCE_LOC1 (0x2)
#define DW_CFA_ADVANCE_LOC2 (0x3)
#define DW_CFA_ADVANCE_LOC4 (0x4)
#define DW_CFA_OFFSET_EXTENDED (0x5)
#define DW_CFA_RESTORE_EXTENDED (0x6)
#define DW_CFA_UNDEFINED (0x7)
#define DW_CFA_SAME_VALUE (0x8)
#define DW_CFA_REGISTER (0x9)
#define DW_CFA_REMEMBER_STATE (0xA)
#define DW_CFA_RESTORE_STATE (0xB)
#define DW_CFA_DEF_CFA (0xC)
#define DW_CFA_DEF_CFA_REGISTER (0xD)
#define DW_CFA_DEF_CFA_OFFSET (0xE)
#define DW_CFA_DEF_CFA_EXPRESSION (0xF)
#define DW_CFA_EXPRESSION (0x10)
#define DW_CFA_OFFSET_EXTENDED_SF (0x11)
#define DW_CFA_DEF_CFA_SF (0x12)
#define DW_CFA_DEF_CFA_OFFSET_SF (0x13)
#define DW_CFA_VAL_OFFSET (0x14)
#define DW_CFA_VAL_OFFSET_SF (0x15)
#define DW_CFA_VAL_EXPRESSION (0x16)
#define DW_CFA_LO_USER (0x1C)
/**
* @brief Constants used for decoding (U)LEB128 integers.
*/
#define DW_LEB128_HIGHEST_BIT(byte) (((byte) >> 7) & 1)
#define DW_LEB128_SIGN_BIT(byte) (((byte) >> 6) & 1)
#define DW_LEB128_MAX_SHIFT (31)
/**
* @brief Symbols defined by the linker.
* Retrieve the addresses of both .eh_frame_hdr and .eh_frame sections.
*/
extern char __eh_frame_hdr;
extern char __eh_frame;
/**
* @brief Decode multiple bytes encoded in LEB128.
*
* @param bytes bytes encoded in LEB128. They will not be modified.
* @param is_signed true if bytes represent a signed value, false else.
* @param size Size in bytes of the encoded value.
*
* @return Decoded bytes.
*/
static uint32_t decode_leb128(const uint8_t* bytes, bool is_signed, uint32_t* lebsize)
{
uint32_t res = 0;
uint32_t shf = 0;
uint32_t size = 0;
uint8_t byte = 0;
while(1) {
byte = bytes[size++];
res |= (byte & 0x7f) << shf;
shf += 7;
if (DW_LEB128_HIGHEST_BIT(byte) == 0)
break;
}
if (is_signed && shf <= DW_LEB128_MAX_SHIFT && DW_LEB128_SIGN_BIT(byte)) {
res |= ((uint32_t) ~0 << shf);
}
if (lebsize) {
*lebsize = size;
}
return res;
}
/**
* @brief Get the value of data encoded.
*
* @param data Pointer to the encoded data.
* @param encoding Encoding for the data to read.
* @param psize Reference to be filled with data size, in bytes.
*
* @return Decoded data read from the pointer.
*/
static uint32_t esp_eh_frame_get_encoded(void* data, uint8_t encoding, uint32_t* psize)
{
int32_t svalue = 0;
uint32_t uvalue = 0;
uint32_t fvalue = 0;
uint32_t size = 0;
const uint32_t high = encoding >> 4;
const uint32_t low = encoding & 0xf;
assert(psize != NULL);
if (encoding == DW_EH_PE_omit) {
*psize = size;
return uvalue;
}
switch (low) {
case DW_EH_PE_udata2:
size = 2;
uvalue = *((uint16_t*) data);
break;
case DW_EH_PE_udata4:
size = 4;
uvalue = *((uint32_t*) data);
break;
case DW_EH_PE_sdata2:
size = 2;
svalue = *((int16_t*) data);
break;
case DW_EH_PE_sdata4:
size = 4;
svalue = *((int32_t*) data);
break;
default:
/* Unsupported yet. */
assert(false);
break;
}
switch (high) {
case DW_EH_PE_absptr:
/* Do not change the values, as one of them will be 0, fvalue will
* contain the data no matter whether it is signed or unsigned. */
fvalue = svalue + uvalue;
break;
case DW_EH_PE_pcrel:
/* Relative to the address of the data.
* svalue has been casted to an 32-bit value, so even if it was a
* 2-byte signed value, fvalue will be calculated correctly here. */
fvalue = (uint32_t) data + svalue + uvalue;
break;
case DW_EH_PE_datarel:
fvalue = (uint32_t) EH_FRAME_HDR_ADDR + svalue + uvalue;
break;
}
*psize = size;
return fvalue;
}
/**
* @brief Find entry in the table for the given return_address.
*
* @param sorted_table Pointer to the sorted table of entries.
* @param length Number of entries in the table.
* @param encoding Encoding for the addresses in the table
* (Check DWARF documentation for more info about encoding).
* @param return_address The address to find in the table. This address can be
* part of one in the function listed.
*
* @note The table is structured like this (after decoding the addresses):
* Function address FDE address Index
* +-------------------------------+
* |0x403805a4 0x4038d014| 0
* +-------------------------------+
* |0x403805be 0x4038d034| 1
* +-------------------------------+
* |0x403805d8 0x4038d070| 2
* +-------------------------------+
* |.......... ..........| ...
* +-------------------------------+
* |0x42020c48 0x4038ddb4| length-3
* +-------------------------------+
* |0x42020dca 0x4038dde4| length-2
*+-------------------------------+
* |0x42020f92 0x4038debc| length-1
* +-------------------------------+
*
* For example, if return_address passed is 0x403805b4, this function will
* return a pointer to the entry (0x403805a4, 0x4038d014).
*
* @return Pointer to the entry found, NULL if not found.
*/
static const table_entry* esp_eh_frame_find_entry(const table_entry* sorted_table,
const uint32_t length,
const uint32_t encoding,
const uint32_t return_address)
{
int32_t ra = 0;
/* Used for decoding addresses in the table. */
uint32_t is_signed = (encoding & 0xf) >= 0x9;
uint32_t pc_relative = true;
/* The following local variables are used for dichotomic search. */
uint32_t found = false;
uint32_t begin = 0;
uint32_t end = length;
uint32_t middle = (end + begin) / 2;
/* If the addresses in the table are offsets relative to the eh_frame section,
* instead of decoding each of them, we can simply encode the return_address
* we have to find. If addresses are offsets relative to the programe counter,
* then we have no other choice than decoding each of them to compare them
* with return_address. */
if (ESP_ENCODING_FRAME_HDR_REL(encoding)) {
ra = return_address - (uint32_t) EH_FRAME_HDR_ADDR;
pc_relative = false;
}
/* Perform dichotomic search. */
while (end != 0 && middle != (length - 1) && !found) {
const uint32_t fun_addr = sorted_table[middle].fun_addr;
const uint32_t nxt_addr = sorted_table[middle + 1].fun_addr;
if (pc_relative) {
ra = return_address - (uint32_t) (sorted_table + middle);
}
if (is_signed) {
/* Signed comparisons. */
const int32_t sfun_addr = (int32_t) fun_addr;
const int32_t snxt_addr = (int32_t) nxt_addr;
if (sfun_addr <= ra && snxt_addr > ra)
found = true;
else if (snxt_addr <= ra)
begin = middle + 1;
else
end = middle;
} else {
/* Unsigned comparisons. */
const uint32_t ura = (uint32_t) ra;
if (fun_addr <= ura && nxt_addr > ura)
found = true;
else if (nxt_addr <= ura)
begin = middle + 1;
else
end = middle;
}
middle = (end + begin) / 2;
}
/* If 'end' reached the beginning of the array, it means the return_address
* passed was below the first address of the array, thus, it was wrong.
* Else, return the address found. */
return (end == 0) ? 0 : sorted_table + middle;
}
/**
* @brief Decode an address according to the encoding passed.
*
* @param addr Pointer to the address to decode.
* This pointer's value MUST be an address in .eh_frame_hdr section.
* @param encoding DWARF encoding byte.
*
* @return address dedoded (e.g. absolute address)
*/
static inline uint32_t* esp_eh_frame_decode_address(const uint32_t* addr,
const uint32_t encoding)
{
uint32_t* decoded = 0;
if (ESP_ENCODING_FRAME_HDR_REL(encoding))
decoded = (uint32_t*) (*addr + (uint32_t) EH_FRAME_HDR_ADDR);
else if (ESP_ENCODING_PC_REL(encoding))
decoded = (uint32_t*) (*addr + (uint32_t) addr);
else
decoded = (uint32_t*) (*addr);
return decoded;
}
/**
* @brief Execute the DWARF instruction which high 2 bits are 0.
*
* @param opcode low 6 bits of the instruction code.
* @param operands pointer to the possible operands.
* @param state state of the DWARF machine. Its registers may be modified.
*
* @return Number of operands used for executing the instruction.
*/
static inline uint32_t esp_eh_frame_execute_opcode_0(const uint32_t opcode, const uint8_t* operands,
dwarf_regs* state)
{
uint32_t operand1 = 0;
uint32_t used_operands = 0;
uint32_t operand2 = 0;
uint32_t used_operands2 = 0;
switch(opcode) {
case DW_CFA_NOP:
break;
case DW_CFA_ADVANCE_LOC1:
/* Advance location with a 1-byte delta. */
used_operands = 1;
state->location += *operands;
break;
case DW_CFA_ADVANCE_LOC2:
/* Advance location with a 2-byte delta. */
used_operands = 2;
state->location += *((const uint16_t*) operands);
break;
case DW_CFA_ADVANCE_LOC4:
/* Advance location with a 4-byte delta. */
used_operands = 4;
state->location += *((const uint32_t*) operands);
break;
case DW_CFA_REMEMBER_STATE:
assert(state->offset_idx == 0);
memcpy(state->regs_offset[1], state->regs_offset[0],
EXECUTION_FRAME_MAX_REGS * sizeof(uint32_t));
state->offset_idx++;
break;
case DW_CFA_RESTORE_STATE:
assert(state->offset_idx == 1);
/* Drop the saved state. */
state->offset_idx--;
break;
case DW_CFA_DEF_CFA:
/* CFA changes according to a register and an offset.
* This instruction appears when the assembly code saves the
* SP in the middle of a routine, before modifying it.
* For example (on RISC-V):
* addi s0, sp, 80
* addi sp, sp, -10
* ... */
/* Operand1 is the register containing the CFA value. */
operand1 = decode_leb128(operands, false, &used_operands);
/* Offset for the register's value. */
operand2 = decode_leb128(operands + used_operands, false, &used_operands2);
/* Calculate the number of bytes */
used_operands += used_operands2;
/* Assert that the register and the offset are valid. */
assert(ESP_EH_FRAME_CFA_REG_VALID(operand1));
assert(ESP_EH_FRAME_CFA_OFF_VALID(operand2));
ESP_EH_FRAME_CFA(state) = ESP_EH_FRAME_NEW_CFA(operand1, operand2);
break;
case DW_CFA_DEF_CFA_REGISTER:
/* Define the register of the current frame address (CFA).
* Its operand is in the next bytes, its type is ULEB128. */
operand1 = decode_leb128(operands, false, &used_operands);
/* Check whether the value is valid or not. */
assert(ESP_EH_FRAME_CFA_OFF_VALID(operand1));
/* Offset will be unchanged, only register changes. */
ESP_EH_FRAME_CFA(state) = ESP_EH_FRAME_SET_CFA_REG(ESP_EH_FRAME_CFA(state), operand1);
break;
case DW_CFA_DEF_CFA_OFFSET:
/* Same as above but for the offset. The register of CFA remains unchanged. */
operand1 = decode_leb128(operands, false, &used_operands);
assert(ESP_EH_FRAME_CFA_OFF_VALID(operand1));
ESP_EH_FRAME_CFA(state) = ESP_EH_FRAME_SET_CFA_OFF(ESP_EH_FRAME_CFA(state), operand1);
break;
default:
panic_print_str("\r\nUnsupported DWARF opcode 0: 0x");
panic_print_hex(opcode);
panic_print_str("\r\n");
used_operands = ESP_EH_FRAME_UNSUPPORTED_OPCODE;
break;
}
return used_operands;
}
/**
* @brief Execute DWARF instructions.
*
* @param instructions Array of instructions to execute.
* @param instructions_length Length of the array of instructions.
* @param frame Execution frame of the crashed task. This will only be used to
* get the PC where the task crashed.
* @param state DWARF machine state. The registers contained in the state will
* modified accordingly to the instructions.
*
* @return true if the execution went fine, false if an unsupported instruction was met.
*/
static bool esp_eh_frame_execute(const uint8_t* instructions, const uint32_t instructions_length,
const ExecutionFrame* frame, dwarf_regs* state)
{
for (uint32_t i = 0; i < instructions_length; i++) {
const uint8_t instr = instructions[i];
const uint8_t param = DW_GET_PARAM(instr);
uint32_t operand1 = 0;
uint32_t size = 0;
uint32_t used_operands = 0;
/* Decode the instructions. According to DWARF documentation, there are three
* types of Call Frame Instructions. The upper 2 bits defines the type. */
switch (DW_GET_OPCODE(instr)) {
case DW_CFA_0_OPCODE:
used_operands = esp_eh_frame_execute_opcode_0(param, &instructions[i + 1], state);
/* Exit the function if an unsupported opcode was met. */
if (used_operands == ESP_EH_FRAME_UNSUPPORTED_OPCODE) {
return false;
}
i += used_operands;
break;
case DW_CFA_ADVANCE_LOC:
/* Move the location forward. This instruction will mark when to stop:
* once we reach the instruction where the PC left, we can break out of the loop
* The delta is part of the lowest 6 bits.
*/
state->location += param;
break;
case DW_CFA_OFFSET:
operand1 = decode_leb128(&instructions[i + 1], false, &size);
assert(ESP_EH_FRAME_CFA_OFFSET_VALID(operand1));
state->regs_offset[state->offset_idx][param] = ESP_EH_FRAME_SET_REG_OFFSET(operand1);
i += size;
break;
case DW_CFA_RESTORE:
state->regs_offset[state->offset_idx][param] = ESP_EH_FRAME_REG_SAME;
break;
default:
/* Illegal opcode */
assert(false);
break;
}
/* As the state->location can also be modified by 0-opcode instructions (in the function)
* and also because we need to break the loop (and not only the switch), let's put this
* check here, after the execution of the instruction, outside of the switch block. */
if (state->location >= EXECUTION_FRAME_PC(*frame))
break;
}
/* Everything went fine, no unsupported opcode was met, return true. */
return true;
}
/**
* @brief Initialize the DWARF registers state by parsing and executing CIE instructions.
*
* @param cie Pointer to the CIE data.
* @param frame Pointer to the execution frame.
* @param state DWARF machine state (DWARF registers).
*
* @return index of the DWARF register containing the return address.
*/
static uint32_t esp_eh_frame_initialize_state(const uint8_t* cie, ExecutionFrame* frame, dwarf_regs* state)
{
char c = 0;
uint32_t size = 0;
/* The first word in the CIE structure is the length of the structure,
* excluding this field itself. */
const uint32_t length = ((uint32_t*) cie)[0];
/* ID of the CIE, should be 0 for .eh_frame (which is our case) */
const uint32_t id = ((uint32_t*) cie)[1];
assert(id == 0);
/* Ignore CIE version (1 byte). */
/* The following data in the structure have variable length as they are
* encoded in (U)LEB128. Thus, let's use a byte pointer to parse them. */
uint8_t* cie_data = (uint8_t*) cie + ESP_CIE_VARIABLE_FIELDS_IDX;
/* Next field is a null-terminated UTF-8 string. Ignore it, look for the end. */
while((c = *cie_data++) != 0);
/* Field alignment factor shall be 1. It is encoded in ULEB128. */
const uint32_t code_align = decode_leb128(cie_data, false, &size);
assert(code_align == 1);
/* Jump to the next field */
cie_data += size;
/* Same goes for data alignment factor. Shall be equal to -4. */
const int32_t data_align = decode_leb128(cie_data, true, &size);
cie_data += size;
assert(data_align == -4);
/* Field describing the index of the DWARF register which will contain
* the return address. */
const uint32_t ra_reg = decode_leb128(cie_data, false, &size);
cie_data += size;
/* Augmentation data length is encoded in ULEB128. It represents the,
* length of the augmentation data. Jump after it to retrieve the
* instructions to execute. */
const uint32_t augmentation_len = decode_leb128(cie_data, false, &size);
cie_data += size + augmentation_len;
/* Calculate the instructions length in order to prevent any out of bounds
* bug. Subtract the offset of this field (minus sizeof(uint32_t) because
* `length` field is not part of the structure length) to the total length
* of the structure. */
const uint32_t instructions_length = length - (cie_data - sizeof(uint32_t) - cie);
/* Execute the instructions contained in CIE structure. Their goal is to
* initialize the DWARF registers. Usually it binds the CFA (virtual stack
* pointer), to its hardware equivalent. It will also bind a hardware
* register to the virtual return address register. For example, x86
* doesn't have a return address register, the address to return to
* it stored on the stack when `call` instruction is used. DWARF will
* use `eip` (instruction pointer, a.k.a. program counter) as a
* register containing the return address register. */
esp_eh_frame_execute(cie_data, instructions_length, frame, state);
return ra_reg;
}
/**
* @brief Modify the execution frame and DWARF VM state for restoring caller's context.
*
* @param fde Pointer to the Frame Description Entry for the current program counter (defined by frame's MEPC register)
* @param frame Snapshot of the CPU registers when the CPU stopped its normal execution.
* @param state DWARF VM registers.
*
* @return Return Address of the current context. Frame has been restored to the previous context
* (before calling the function program counter is currently going throught).
*/
static uint32_t esp_eh_frame_restore_caller_state(const uint32_t* fde,
ExecutionFrame* frame,
dwarf_regs* state)
{
/* Length of the whole Frame Description Entry (FDE), excluding this field. */
const uint32_t length = fde[ESP_FDE_LENGTH_IDX];
/* The addresses in FDE are relative to the location of each field.
* Thus, to get the absolute address of the function it is pointing to,
* we have to compute:
* fun_addr = &fde[IDX] +/- fde[IDX]
*/
const uint8_t* cie = (uint8_t*) ((uint32_t) &fde[ESP_FDE_CIE_IDX] - fde[ESP_FDE_CIE_IDX]);
const uint32_t initial_location = ((uint32_t) &fde[ESP_FDE_INITLOC_IDX] + fde[ESP_FDE_INITLOC_IDX]);
const uint32_t range_length = fde[ESP_FDE_RANGELEN_IDX];
const uint8_t augmentation = *((uint8_t*) (fde + ESP_FDE_AUGMENTATION_IDX));
/* The length, in byte, of the instructions is the size of the FDE header minus
* the above fields' length. */
const uint32_t instructions_length = length - 3 * sizeof(uint32_t) - sizeof(uint8_t);
const uint8_t* instructions = ((uint8_t*) (fde + ESP_FDE_AUGMENTATION_IDX)) + 1;
/* Make sure this FDE is the correct one for the PC given. */
assert(initial_location <= EXECUTION_FRAME_PC(*frame) &&
EXECUTION_FRAME_PC(*frame) < initial_location + range_length);
/* Augmentation not supported. */
assert(augmentation == 0);
/* Initialize the DWARF state by executing the CIE's instructions. */
const uint32_t ra_reg = esp_eh_frame_initialize_state(cie, frame, state);
state->location = initial_location;
/**
* Execute the DWARf instructions is order to create rules that will be executed later to retrieve
* the registers former value.
*/
bool success = esp_eh_frame_execute(instructions, instructions_length, frame, state);
if (!success) {
/* An error occured (unsupported opcode), return PC as the return address.
* This will be tested by the caller, and the backtrace will be finished. */
return EXECUTION_FRAME_PC(*frame);
}
/* Execute the rules calculated previously. Start with the CFA. */
const uint32_t cfa_val = ESP_EH_FRAME_CFA(state);
const uint32_t cfa_reg = ESP_EH_FRAME_GET_CFA_REG(cfa_val);
const uint32_t cfa_off = ESP_EH_FRAME_GET_CFA_OFF(cfa_val);
const uint32_t cfa_addr = EXECUTION_FRAME_REG(frame, cfa_reg) + cfa_off;
/* Restore the registers that need to be restored. */
for (uint32_t i = 0; i < DIM(state->regs_offset[0]); i++) {
uint32_t value_addr = state->regs_offset[state->offset_idx][i];
/* Check that the value changed and that we are not treating the CFA register (if it is part of the array). */
if (i != ESP_ESH_FRAME_CFA_IDX && value_addr != ESP_EH_FRAME_REG_SAME) {
/* value_addr contains a description of how to find its address:
* it has an offset relative to the CFA, which will point to the actual former value.
* In fact, the register's previous value (in the context of the caller) is on the stack,
* this is what value_addr will point to. */
value_addr = cfa_addr - ESP_EH_FRAME_GET_REG_OFFSET(value_addr) * sizeof(uint32_t);
EXECUTION_FRAME_REG(frame, i) = *((uint32_t*) value_addr);
}
}
/* Restore the stack pointer according to DWARF CFA register. */
EXECUTION_FRAME_SP(*frame) = cfa_addr;
/* If the frame was not available, it would be possible to retrieve the return address
* register thanks to CIE structure.
* The return address points to the address the PC needs to jump to. It
* does NOT point to the instruction where the routine call occured.
* This can cause problems with functions without epilogue (i.e. function
* which last instruction is a function call). This happens when compiler
* optimization are ON or when a function is marked as "noreturn".
*
* Thus, in order to point to the call/jal instruction, we need to
* subtract at least 1 byte but not more than an instruction size.
*/
return EXECUTION_FRAME_REG(frame, ra_reg) - 2;
}
/**
* @brief Test whether the DWARF information for the given PC are missing or not.
*
* @param fde FDE associated to this PC. This FDE is the one found thanks to
* `esp_eh_frame_find_entry()`.
* @param pc PC to get information from.
*
* @return true is DWARF information are missing, false else.
*/
static bool esp_eh_frame_missing_info(const uint32_t* fde, uint32_t pc) {
if (fde == NULL) {
return true;
}
/* Get the range of this FDE entry. It is possible that there are some
* gaps between DWARF entries, in that case, the FDE entry found has
* indeed an initial_location very close to PC but doesn't reach it.
* For example, if FDE initial_location is 0x40300000 and its length is
* 0x100, but PC value is 0x40300200, then some DWARF information
* are missing as there is a gap.
* End the backtrace. */
const uint32_t initial_location = ((uint32_t) &fde[ESP_FDE_INITLOC_IDX] + fde[ESP_FDE_INITLOC_IDX]);
const uint32_t range_length = fde[ESP_FDE_RANGELEN_IDX];
return (initial_location + range_length) <= pc;
}
/**
* @brief When one step of the backtrace is generated, output it to the serial.
* This function can be overriden as it is defined as weak.
*
* @param pc Program counter of the backtrace step.
* @param sp Stack pointer of the backtrace step.
*/
void __attribute__((weak)) esp_eh_frame_generated_step(uint32_t pc, uint32_t sp)
{
panic_print_str(" 0x");
panic_print_hex(pc);
panic_print_str(":0x");
panic_print_hex(sp);
}
/**
* @brief Print backtrace for the given execution frame.
*
* @param frame_or Snapshot of the CPU registers when the CPU stopped its normal execution.
*/
void esp_eh_frame_print_backtrace(const void *frame_or)
{
assert(frame_or != NULL);
static dwarf_regs state = { 0 };
ExecutionFrame frame = *((ExecutionFrame*) frame_or);
uint32_t size = 0;
uint8_t* enc_values = NULL;
bool end_of_backtrace = false;
/* Start parsing the .eh_frame_hdr section. */
fde_header* header = (fde_header*) EH_FRAME_HDR_ADDR;
assert(header->version == 1);
/* Make enc_values point to the end of the structure, where the encoded
* values start. */
enc_values = (uint8_t*) (header + 1);
/* Retrieve the encoded value eh_frame_ptr. Get the size of the data also. */
const uint32_t eh_frame_ptr = esp_eh_frame_get_encoded(enc_values, header->eh_frame_ptr_enc, &size);
assert(eh_frame_ptr == (uint32_t) EH_FRAME_ADDR);
enc_values += size;
/* Same for the number of entries in the sorted table. */
const uint32_t fde_count = esp_eh_frame_get_encoded(enc_values, header->fde_count_enc, &size);
enc_values += size;
/* enc_values points now at the beginning of the sorted table. */
/* Only support 4-byte entries. */
const uint32_t table_enc = header->table_enc;
assert(((table_enc >> 4) == 0x3) || ((table_enc >> 4) == 0xB));
const table_entry* sorted_table = (const table_entry*) enc_values;
panic_print_str("Backtrace:");
while (!end_of_backtrace) {
/* Output one step of the backtrace. */
esp_eh_frame_generated_step(EXECUTION_FRAME_PC(frame), EXECUTION_FRAME_SP(frame));
const table_entry* from_fun = esp_eh_frame_find_entry(sorted_table, fde_count,
table_enc, EXECUTION_FRAME_PC(frame));
/* Get absolute address of FDE entry describing the function where PC left of. */
uint32_t* fde = NULL;
if (from_fun != NULL) {
fde = esp_eh_frame_decode_address(&from_fun->fde_addr, table_enc);
}
if (esp_eh_frame_missing_info(fde, EXECUTION_FRAME_PC(frame))) {
/* Address was not found in the list. */
panic_print_str("\r\nBacktrace ended abruptly: cannot find DWARF information for"
" instruction at address 0x");
panic_print_hex(EXECUTION_FRAME_PC(frame));
panic_print_str("\r\n");
break;
}
/* Clean and set the DWARF register structure. */
memset(&state, 0, sizeof(dwarf_regs));
const uint32_t prev_sp = EXECUTION_FRAME_SP(frame);
/* Retrieve the return address of the frame. The frame's registers will be modified.
* The frame we get then is the caller's one. */
uint32_t ra = esp_eh_frame_restore_caller_state(fde, &frame, &state);
/* End of backtrace is reached if the stack and the PC don't change anymore. */
end_of_backtrace = (EXECUTION_FRAME_SP(frame) == prev_sp) && (EXECUTION_FRAME_PC(frame) == ra);
/* Go back to the caller: update stack pointer and program counter. */
EXECUTION_FRAME_PC(frame) = ra;
}
panic_print_str("\r\n");
}
#endif //ESP_SYSTEM_USE_EH_FRAME
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