/*
* SPDX-FileCopyrightText: 2020-2022 Espressif Systems (Shanghai) CO LTD
*
* SPDX-License-Identifier: Apache-2.0
*/
/**
* @file DWARF Exception Frames parser header
*
* This file describes the frame types for x86, required for
* parsing `eh_frame` and `eh_frame_hdr`.
*/
#define _POSIX_C_SOURCE 200809L
#define _DEFAULT_SOURCE
#include <stdio.h>
#include <signal.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdbool.h>
#include <assert.h>
#include <ucontext.h>
#include "../include/esp_private/eh_frame_parser.h"
#include "eh_frame_parser_impl.h"
/**
* @brief Index of x86 registers in `greg_t` structure.
*/
#define REG_EDI 4
#define REG_ESI 5
#define REG_EBP 6
#define REG_ESP 7
#define REG_EBX 8
#define REG_EDX 9
#define REG_ECX 10
#define REG_EAX 11
#define REG_EIP 14
/**
* @brief Number of functions in the funs structure described below.
*/
#define FUNCTIONS_COUNT ((sizeof(funs)/sizeof(*funs)))
/**
* @brief Number which will determine the depth of the call stack.
* Check `main()` for more information.
*/
#define NUMBER_TO_TEST (4)
/**
* @brief Number of iteration for function `esp_eh_frame_generated_step`.
*/
#define NUMBER_OF_ITERATION (2 * NUMBER_TO_TEST + 2 + 1)
/**
* @brief Define a simple linked list type and initialize one.
*/
struct list_t {
uint32_t value;
struct list_t *next;
};
static struct list_t head = { 0 };
/**
* Few recursive functions to make the the call stack a bit more complex than a
* single function call would give.
*/
bool is_odd(uint32_t n);
bool is_even(uint32_t n);
void browse_list(struct list_t* l);
/**
* @brief Structure defining a function of our program.
* This will be used to translate the backtrace.
*/
struct functions_info {
const char* name;
uintptr_t start;
uintptr_t end; /* will be filled at runtime */
};
/**
* @brief Structure storing the information about the
* function that will be part of the backtrace.
*/
struct functions_info funs[] = {
{
.name = "browse_list",
.start = (uintptr_t) &browse_list,
.end = 0
},
{
.name = "is_odd",
.start = (uintptr_t) &is_odd,
.end = 0
},
{
.name = "is_even",
.start = (uintptr_t) &is_even,
.end = 0
}
};
/**
* @brief Test whether the address passed as PC is part of the function which
* name is `function_name`. The global array `funs` is used.
*
* @param pc Program counter to test. (address in the program)
* @param function_name Function name to check the address of.
*
* @return true if PC is in the function called `function_name`, false else.
*/
bool is_pc_in_function(const uint32_t pc, const char* function_name)
{
for (uint32_t i = 0; i < FUNCTIONS_COUNT; i++) {
const struct functions_info current_fun = funs[i];
if (strcmp(current_fun.name, function_name) == 0) {
return current_fun.start <= pc && pc <= current_fun.end;
}
}
/* Function not found. */
return false;
}
/**
* @brief Number of times `esp_eh_frame_generated_step` is called.
*/
static uint32_t iteration = 1;
/**
* @brief Override the default function called when a backtrace step is
* generated.
*/
void esp_eh_frame_generated_step(uint32_t pc, uint32_t sp) {
/* The first PCs in the backtrace are calls to `browse_list()` + 2.
* This is due to the fact that the list contains all the numbers
* between NUMBER_TO_TEST to 0 included. Moreover, another call
* is made when we meet the NULL pointer. */
if (iteration > 0 && iteration <= (NUMBER_TO_TEST + 2)) {
assert(is_pc_in_function(pc, "browse_list"));
} else {
/**
* The backtrace should be:
* - in is_odd when iteration is even.
* - in is_even when iteration is odd.
*
* The backtrace finishes when the iteration reaches the end of
* browse_list (NUMBER_TO_TEST + 2 iterations), is_even
* (NUMBER_TO_TEST/2 calls) and is_odd (NUMBER_TO_TEST/2 calls) calls.
*/
if (iteration >= NUMBER_OF_ITERATION)
return;
else if (iteration % 2 == 0)
assert(is_pc_in_function(pc, "is_odd"));
else
assert(is_pc_in_function(pc, "is_even"));
}
/* Number of times this function has been entered. */
iteration++;
}
/**
* @brief Handler called when SIGSEV signal is sent to the program.
*
* @param signal Signal received byt the program. Shall be SIGSEGV.
* @param info Structure containing info about the error itself. Ignored.
* @param ucontext Context of the program when the error occurred. This
* is used to retrieve the CPU registers value.
*/
void signal_handler(int signal, siginfo_t *info, void *ucontext) {
/* Setup the execution frame as expected by the eh_frame_parser.
* Indeed, the registers index defined in ucontext.h are NOT the same
* the registers index DWARF is expecting. */
ucontext_t* context = (ucontext_t*) ucontext;
greg_t *gregset = context->uc_mcontext.gregs;
x86ExcFrame frame = {
.eax = gregset[REG_EAX],
.ecx = gregset[REG_ECX],
.edx = gregset[REG_EDX],
.ebx = gregset[REG_EBX],
.esp = gregset[REG_ESP],
.ebp = gregset[REG_EBP],
.esi = gregset[REG_ESI],
.edi = gregset[REG_EDI],
.eip = gregset[REG_EIP]
};
/* The following function will use panic_print_str and panic_print_hex
* function to output the data.
* Instead of replacing stdout file descriptor with a pipe, we can simply
* replace these functions to store the data instead of printing them.
*/
esp_eh_frame_print_backtrace(&frame);
/* No assert has been triggered, the backtrace succeeded if the number of
* iterations of function `esp_eh_frame_generated_step` is correct. */
if (iteration == NUMBER_OF_ITERATION) {
printf("\e[32m\e[1mAll tests passed \e[0m\r\n");
} else {
printf("\e[31m\e[1mWrong length of backtrace (%d iteration, expected %d) \e[0m\r\n",
iteration, NUMBER_OF_ITERATION);
exit(1);
}
/* Everything went fine, exit normally. */
exit(0);
}
/**
* @brief Browse the list passed as an argument.
* The following function will trigger a SIGSEV signal on purpose, in order to
* generate the backtrace.
*
* @param l List to browse.
*/
void browse_list(struct list_t* l) {
browse_list(l->next);
}
/**
* @brief Add a number to the global list `head`.
*
* @param n Number to add in the list.
*/
void add_number_to_list(uint32_t n) {
struct list_t* l = malloc(sizeof(struct list_t));
l->value = n;
l->next = head.next;
head.next = l;
}
/**
* @brief Test if the number passed is even.
* This function will fail, on purpose.
*
* @param n Number to test.
*
* @return true if even, false else.
*/
bool is_even(uint32_t n) {
add_number_to_list(n);
if (n == 0) {
browse_list(head.next);
return true;
}
return is_odd(n - 1);
}
/**
* @brief Test if the number passed is odd.
* This function will fail, on purpose.
*
* @param n Number to test.
*
* @return true if odd, false else.
*/
bool is_odd(uint32_t n) {
add_number_to_list(n);
if (n == 0) {
browse_list(head.next);
return false;
}
return is_even(n - 1);
}
/**
* @brief Initiliaze the global `funs` array.
*/
static inline void initialize_functions_info(void)
{
for (uint32_t i = 0; i < FUNCTIONS_COUNT; i++) {
/* Each of the functions defined in this structure finishes
* with the following instructions:
* leave (0xc9)
* ret (0xc3)
* Thus, we will look for these instructions. */
uint8_t* instructions = (uint8_t*) funs[i].start;
while (instructions[0] != 0xc9 || instructions[1] != 0xc3)
instructions++;
instructions += 1;
funs[i].end = (uintptr_t) instructions;
}
}
/**
* Call the previous functions to create a complex call stack and fail.
*/
int main (int argc, char** argv)
{
/* Initialize the structure holding information about the signal to override. */
struct sigaction sig = {
.sa_mask = 0,
.sa_flags = SA_SIGINFO,
.sa_restorer = NULL,
.sa_sigaction = signal_handler
};
/* Look for the functions end functions. */
initialize_functions_info();
/* Override default SIGSEV signal callback. */
int res = sigaction(SIGSEGV, &sig, NULL);
if (res) {
perror("Could not override SIGSEV signal");
return 1;
}
/* Trigger the segmentation fault with a complex backtrace. */
is_even(NUMBER_TO_TEST);
return 0;
}