Douglas Raillard | 0c62883 | 2018-08-21 12:54:45 +0100 | [diff] [blame] | 1 | /* |
| 2 | * Copyright (c) 2018, ARM Limited and Contributors. All rights reserved. |
| 3 | * |
| 4 | * SPDX-License-Identifier: BSD-3-Clause |
| 5 | */ |
| 6 | |
| 7 | #include <arch_helpers.h> |
| 8 | #include <assert.h> |
| 9 | #include <console.h> |
| 10 | #include <debug.h> |
| 11 | #include <stdbool.h> |
| 12 | #include <stdint.h> |
| 13 | |
| 14 | /* Maximum number of entries in the backtrace to display */ |
| 15 | #define UNWIND_LIMIT 20U |
| 16 | |
| 17 | /* |
| 18 | * If -fno-omit-frame-pointer is used: |
| 19 | * |
| 20 | * - AArch64: The AAPCS defines the format of the frame records and mandates the |
| 21 | * usage of r29 as frame pointer. |
| 22 | * |
| 23 | * - AArch32: The format of the frame records is not defined in the AAPCS. |
| 24 | * However, at least GCC and Clang use the same format. When they are forced |
| 25 | * to only generate A32 code (with -marm), they use r11 as frame pointer and a |
| 26 | * similar format as in AArch64. If interworking with T32 is enabled, the |
| 27 | * frame pointer is r7 and the format is different. This is not supported by |
| 28 | * this implementation of backtrace, so it is needed to use -marm. |
| 29 | */ |
| 30 | |
| 31 | /* Frame records form a linked list in the stack */ |
| 32 | struct frame_record { |
| 33 | /* Previous frame record in the list */ |
| 34 | struct frame_record *parent; |
| 35 | /* Return address of the function at this level */ |
| 36 | uintptr_t return_addr; |
| 37 | }; |
| 38 | |
| 39 | static const char *get_el_str(unsigned int el) |
| 40 | { |
| 41 | if (el == 3U) { |
| 42 | return "EL3"; |
| 43 | } else if (el == 2U) { |
| 44 | return "EL2"; |
| 45 | } else { |
| 46 | return "S-EL1"; |
| 47 | } |
| 48 | } |
| 49 | |
| 50 | /* |
| 51 | * Returns true if the address points to a virtual address that can be read at |
| 52 | * the current EL, false otherwise. |
| 53 | */ |
| 54 | #ifdef AARCH64 |
| 55 | static bool is_address_readable(uintptr_t addr) |
| 56 | { |
| 57 | unsigned int el = get_current_el(); |
| 58 | |
| 59 | if (el == 3U) { |
| 60 | ats1e3r(addr); |
| 61 | } else if (el == 2U) { |
| 62 | ats1e2r(addr); |
| 63 | } else { |
| 64 | ats1e1r(addr); |
| 65 | } |
| 66 | |
| 67 | isb(); |
| 68 | |
| 69 | /* If PAR.F == 1 the address translation was aborted. */ |
| 70 | if ((read_par_el1() & PAR_F_MASK) != 0U) |
| 71 | return false; |
| 72 | |
| 73 | return true; |
| 74 | } |
| 75 | #else /* if AARCH32 */ |
| 76 | static bool is_address_readable(uintptr_t addr) |
| 77 | { |
| 78 | unsigned int el = get_current_el(); |
| 79 | |
| 80 | if (el == 3U) { |
| 81 | write_ats1cpr(addr); |
| 82 | } else if (el == 2U) { |
| 83 | write_ats1hr(addr); |
| 84 | } else { |
| 85 | write_ats1cpr(addr); |
| 86 | } |
| 87 | |
| 88 | isb(); |
| 89 | |
| 90 | /* If PAR.F == 1 the address translation was aborted. */ |
| 91 | if ((read64_par() & PAR_F_MASK) != 0U) |
| 92 | return false; |
| 93 | |
| 94 | return true; |
| 95 | } |
| 96 | #endif |
| 97 | |
| 98 | /* |
| 99 | * Returns true if all the bytes in a given object are in mapped memory and an |
| 100 | * LDR using this pointer would succeed, false otherwise. |
| 101 | */ |
| 102 | static bool is_valid_object(uintptr_t addr, size_t size) |
| 103 | { |
| 104 | assert(size > 0U); |
| 105 | |
| 106 | if (addr == 0U) |
| 107 | return false; |
| 108 | |
| 109 | /* Detect overflows */ |
| 110 | if ((addr + size) < addr) |
| 111 | return false; |
| 112 | |
| 113 | /* A pointer not aligned properly could trigger an alignment fault. */ |
| 114 | if ((addr & (sizeof(uintptr_t) - 1U)) != 0U) |
| 115 | return false; |
| 116 | |
| 117 | /* Check that all the object is readable */ |
| 118 | for (size_t i = 0; i < size; i++) { |
| 119 | if (!is_address_readable(addr + i)) |
| 120 | return false; |
| 121 | } |
| 122 | |
| 123 | return true; |
| 124 | } |
| 125 | |
| 126 | /* |
| 127 | * Returns true if the specified address is correctly aligned and points to a |
| 128 | * valid memory region. |
| 129 | */ |
| 130 | static bool is_valid_jump_address(uintptr_t addr) |
| 131 | { |
| 132 | if (addr == 0U) |
| 133 | return false; |
| 134 | |
| 135 | /* Check alignment. Both A64 and A32 use 32-bit opcodes */ |
| 136 | if ((addr & (sizeof(uint32_t) - 1U)) != 0U) |
| 137 | return false; |
| 138 | |
| 139 | if (!is_address_readable(addr)) |
| 140 | return false; |
| 141 | |
| 142 | return true; |
| 143 | } |
| 144 | |
| 145 | /* |
| 146 | * Returns true if the pointer points at a valid frame record, false otherwise. |
| 147 | */ |
| 148 | static bool is_valid_frame_record(struct frame_record *fr) |
| 149 | { |
| 150 | return is_valid_object((uintptr_t)fr, sizeof(struct frame_record)); |
| 151 | } |
| 152 | |
| 153 | /* |
| 154 | * Adjust the frame-pointer-register value by 4 bytes on AArch32 to have the |
| 155 | * same layout as AArch64. |
| 156 | */ |
| 157 | static struct frame_record *adjust_frame_record(struct frame_record *fr) |
| 158 | { |
| 159 | #ifdef AARCH64 |
| 160 | return fr; |
| 161 | #else |
| 162 | return (struct frame_record *)((uintptr_t)fr - 4U); |
| 163 | #endif |
| 164 | } |
| 165 | |
| 166 | static void unwind_stack(struct frame_record *fr, uintptr_t current_pc, |
| 167 | uintptr_t link_register) |
| 168 | { |
| 169 | uintptr_t call_site; |
| 170 | static const char *backtrace_str = "%u: %s: 0x%lx\n"; |
| 171 | const char *el_str = get_el_str(get_current_el()); |
| 172 | |
| 173 | if (!is_valid_frame_record(fr)) { |
| 174 | printf("ERROR: Corrupted frame pointer (frame record address = %p)\n", |
| 175 | fr); |
| 176 | return; |
| 177 | } |
| 178 | |
| 179 | if (fr->return_addr != link_register) { |
| 180 | printf("ERROR: Corrupted stack (frame record address = %p)\n", |
| 181 | fr); |
| 182 | return; |
| 183 | } |
| 184 | |
| 185 | /* The level 0 of the backtrace is the current backtrace function */ |
| 186 | printf(backtrace_str, 0U, el_str, current_pc); |
| 187 | |
| 188 | /* |
| 189 | * The last frame record pointer in the linked list at the beginning of |
| 190 | * the stack should be NULL unless stack is corrupted. |
| 191 | */ |
| 192 | for (unsigned int i = 1U; i < UNWIND_LIMIT; i++) { |
| 193 | /* If an invalid frame record is found, exit. */ |
| 194 | if (!is_valid_frame_record(fr)) |
| 195 | return; |
| 196 | /* |
| 197 | * A32 and A64 are fixed length so the address from where the |
| 198 | * call was made is the instruction before the return address, |
| 199 | * which is always 4 bytes before it. |
| 200 | */ |
| 201 | call_site = fr->return_addr - 4U; |
| 202 | |
| 203 | /* |
| 204 | * If the address is invalid it means that the frame record is |
| 205 | * probably corrupted. |
| 206 | */ |
| 207 | if (!is_valid_jump_address(call_site)) |
| 208 | return; |
| 209 | |
| 210 | printf(backtrace_str, i, el_str, call_site); |
| 211 | |
| 212 | fr = adjust_frame_record(fr->parent); |
| 213 | } |
| 214 | |
| 215 | printf("ERROR: Max backtrace depth reached\n"); |
| 216 | } |
| 217 | |
| 218 | /* |
| 219 | * Display a backtrace. The cookie string parameter is displayed along the |
| 220 | * trace to help filter the log messages. |
| 221 | * |
| 222 | * Many things can prevent displaying the expected backtrace. For example, |
| 223 | * compiler optimizations can use a branch instead of branch with link when it |
| 224 | * detects a tail call. The backtrace level for this caller will not be |
| 225 | * displayed, as it does not appear in the call stack anymore. Also, assembly |
| 226 | * functions will not be displayed unless they setup AAPCS compliant frame |
| 227 | * records on AArch64 and compliant with GCC-specific frame record format on |
| 228 | * AArch32. |
| 229 | * |
| 230 | * Usage of the trace: addr2line can be used to map the addresses to function |
| 231 | * and source code location when given the ELF file compiled with debug |
| 232 | * information. The "-i" flag is highly recommended to improve display of |
| 233 | * inlined function. The *.dump files generated when buildidng each image can |
| 234 | * also be used. |
| 235 | * |
| 236 | * WARNING: In case of corrupted stack, this function could display security |
| 237 | * sensitive information past the beginning of the stack so it must not be used |
| 238 | * in production build. This function is only compiled in when ENABLE_BACKTRACE |
| 239 | * is set to 1. |
| 240 | */ |
| 241 | void backtrace(const char *cookie) |
| 242 | { |
| 243 | uintptr_t return_address = (uintptr_t)__builtin_return_address(0U); |
| 244 | struct frame_record *fr = __builtin_frame_address(0U); |
| 245 | |
| 246 | /* Printing the backtrace may crash the system, flush before starting */ |
| 247 | (void)console_flush(); |
| 248 | |
| 249 | fr = adjust_frame_record(fr); |
| 250 | |
| 251 | printf("BACKTRACE: START: %s\n", cookie); |
| 252 | |
| 253 | unwind_stack(fr, (uintptr_t)&backtrace, return_address); |
| 254 | |
| 255 | printf("BACKTRACE: END: %s\n", cookie); |
| 256 | } |