| 1 | /* Target-dependent code for Linux running on i386's, for GDB. |
| 2 | Copyright (C) 2000 Free Software Foundation, Inc. |
| 3 | |
| 4 | This file is part of GDB. |
| 5 | |
| 6 | This program is free software; you can redistribute it and/or modify |
| 7 | it under the terms of the GNU General Public License as published by |
| 8 | the Free Software Foundation; either version 2 of the License, or |
| 9 | (at your option) any later version. |
| 10 | |
| 11 | This program is distributed in the hope that it will be useful, |
| 12 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 14 | GNU General Public License for more details. |
| 15 | |
| 16 | You should have received a copy of the GNU General Public License |
| 17 | along with this program; if not, write to the Free Software |
| 18 | Foundation, Inc., 59 Temple Place - Suite 330, |
| 19 | Boston, MA 02111-1307, USA. */ |
| 20 | |
| 21 | #include "defs.h" |
| 22 | #include "gdbcore.h" |
| 23 | #include "frame.h" |
| 24 | #include "value.h" |
| 25 | |
| 26 | \f |
| 27 | /* Recognizing signal handler frames. */ |
| 28 | |
| 29 | /* Linux has two flavors of signals. Normal signal handlers, and |
| 30 | "realtime" (RT) signals. The RT signals can provide additional |
| 31 | information to the signal handler if the SA_SIGINFO flag is set |
| 32 | when establishing a signal handler using `sigaction'. It is not |
| 33 | unlikely that future versions of Linux will support SA_SIGINFO for |
| 34 | normal signals too. */ |
| 35 | |
| 36 | /* When the i386 Linux kernel calls a signal handler and the |
| 37 | SA_RESTORER flag isn't set, the return address points to a bit of |
| 38 | code on the stack. This function returns whether the PC appears to |
| 39 | be within this bit of code. |
| 40 | |
| 41 | The instruction sequence for normal signals is |
| 42 | pop %eax |
| 43 | mov $0x77,%eax |
| 44 | int $0x80 |
| 45 | or 0x58 0xb8 0x77 0x00 0x00 0x00 0xcd 0x80. |
| 46 | |
| 47 | Checking for the code sequence should be somewhat reliable, because |
| 48 | the effect is to call the system call sigreturn. This is unlikely |
| 49 | to occur anywhere other than a signal trampoline. |
| 50 | |
| 51 | It kind of sucks that we have to read memory from the process in |
| 52 | order to identify a signal trampoline, but there doesn't seem to be |
| 53 | any other way. The IN_SIGTRAMP macro in tm-linux.h arranges to |
| 54 | only call us if no function name could be identified, which should |
| 55 | be the case since the code is on the stack. |
| 56 | |
| 57 | Detection of signal trampolines for handlers that set the |
| 58 | SA_RESTORER flag is in general not possible. Unfortunately this is |
| 59 | what the GNU C Library has been doing for quite some time now. |
| 60 | However, as of version 2.1.2, the GNU C Library uses signal |
| 61 | trampolines (named __restore and __restore_rt) that are identical |
| 62 | to the ones used by the kernel. Therefore, these trampolines are |
| 63 | supported too. */ |
| 64 | |
| 65 | #define LINUX_SIGTRAMP_INSN0 (0x58) /* pop %eax */ |
| 66 | #define LINUX_SIGTRAMP_OFFSET0 (0) |
| 67 | #define LINUX_SIGTRAMP_INSN1 (0xb8) /* mov $NNNN,%eax */ |
| 68 | #define LINUX_SIGTRAMP_OFFSET1 (1) |
| 69 | #define LINUX_SIGTRAMP_INSN2 (0xcd) /* int */ |
| 70 | #define LINUX_SIGTRAMP_OFFSET2 (6) |
| 71 | |
| 72 | static const unsigned char linux_sigtramp_code[] = |
| 73 | { |
| 74 | LINUX_SIGTRAMP_INSN0, /* pop %eax */ |
| 75 | LINUX_SIGTRAMP_INSN1, 0x77, 0x00, 0x00, 0x00, /* mov $0x77,%eax */ |
| 76 | LINUX_SIGTRAMP_INSN2, 0x80 /* int $0x80 */ |
| 77 | }; |
| 78 | |
| 79 | #define LINUX_SIGTRAMP_LEN (sizeof linux_sigtramp_code) |
| 80 | |
| 81 | /* If PC is in a sigtramp routine, return the address of the start of |
| 82 | the routine. Otherwise, return 0. */ |
| 83 | |
| 84 | static CORE_ADDR |
| 85 | i386_linux_sigtramp_start (CORE_ADDR pc) |
| 86 | { |
| 87 | unsigned char buf[LINUX_SIGTRAMP_LEN]; |
| 88 | |
| 89 | /* We only recognize a signal trampoline if PC is at the start of |
| 90 | one of the three instructions. We optimize for finding the PC at |
| 91 | the start, as will be the case when the trampoline is not the |
| 92 | first frame on the stack. We assume that in the case where the |
| 93 | PC is not at the start of the instruction sequence, there will be |
| 94 | a few trailing readable bytes on the stack. */ |
| 95 | |
| 96 | if (read_memory_nobpt (pc, (char *) buf, LINUX_SIGTRAMP_LEN) != 0) |
| 97 | return 0; |
| 98 | |
| 99 | if (buf[0] != LINUX_SIGTRAMP_INSN0) |
| 100 | { |
| 101 | int adjust; |
| 102 | |
| 103 | switch (buf[0]) |
| 104 | { |
| 105 | case LINUX_SIGTRAMP_INSN1: |
| 106 | adjust = LINUX_SIGTRAMP_OFFSET1; |
| 107 | break; |
| 108 | case LINUX_SIGTRAMP_INSN2: |
| 109 | adjust = LINUX_SIGTRAMP_OFFSET2; |
| 110 | break; |
| 111 | default: |
| 112 | return 0; |
| 113 | } |
| 114 | |
| 115 | pc -= adjust; |
| 116 | |
| 117 | if (read_memory_nobpt (pc, (char *) buf, LINUX_SIGTRAMP_LEN) != 0) |
| 118 | return 0; |
| 119 | } |
| 120 | |
| 121 | if (memcmp (buf, linux_sigtramp_code, LINUX_SIGTRAMP_LEN) != 0) |
| 122 | return 0; |
| 123 | |
| 124 | return pc; |
| 125 | } |
| 126 | |
| 127 | /* This function does the same for RT signals. Here the instruction |
| 128 | sequence is |
| 129 | mov $0xad,%eax |
| 130 | int $0x80 |
| 131 | or 0xb8 0xad 0x00 0x00 0x00 0xcd 0x80. |
| 132 | |
| 133 | The effect is to call the system call rt_sigreturn. */ |
| 134 | |
| 135 | #define LINUX_RT_SIGTRAMP_INSN0 (0xb8) /* mov $NNNN,%eax */ |
| 136 | #define LINUX_RT_SIGTRAMP_OFFSET0 (0) |
| 137 | #define LINUX_RT_SIGTRAMP_INSN1 (0xcd) /* int */ |
| 138 | #define LINUX_RT_SIGTRAMP_OFFSET1 (5) |
| 139 | |
| 140 | static const unsigned char linux_rt_sigtramp_code[] = |
| 141 | { |
| 142 | LINUX_RT_SIGTRAMP_INSN0, 0xad, 0x00, 0x00, 0x00, /* mov $0xad,%eax */ |
| 143 | LINUX_RT_SIGTRAMP_INSN1, 0x80 /* int $0x80 */ |
| 144 | }; |
| 145 | |
| 146 | #define LINUX_RT_SIGTRAMP_LEN (sizeof linux_rt_sigtramp_code) |
| 147 | |
| 148 | /* If PC is in a RT sigtramp routine, return the address of the start |
| 149 | of the routine. Otherwise, return 0. */ |
| 150 | |
| 151 | static CORE_ADDR |
| 152 | i386_linux_rt_sigtramp_start (CORE_ADDR pc) |
| 153 | { |
| 154 | unsigned char buf[LINUX_RT_SIGTRAMP_LEN]; |
| 155 | |
| 156 | /* We only recognize a signal trampoline if PC is at the start of |
| 157 | one of the two instructions. We optimize for finding the PC at |
| 158 | the start, as will be the case when the trampoline is not the |
| 159 | first frame on the stack. We assume that in the case where the |
| 160 | PC is not at the start of the instruction sequence, there will be |
| 161 | a few trailing readable bytes on the stack. */ |
| 162 | |
| 163 | if (read_memory_nobpt (pc, (char *) buf, LINUX_RT_SIGTRAMP_LEN) != 0) |
| 164 | return 0; |
| 165 | |
| 166 | if (buf[0] != LINUX_RT_SIGTRAMP_INSN0) |
| 167 | { |
| 168 | if (buf[0] != LINUX_RT_SIGTRAMP_INSN1) |
| 169 | return 0; |
| 170 | |
| 171 | pc -= LINUX_RT_SIGTRAMP_OFFSET1; |
| 172 | |
| 173 | if (read_memory_nobpt (pc, (char *) buf, LINUX_RT_SIGTRAMP_LEN) != 0) |
| 174 | return 0; |
| 175 | } |
| 176 | |
| 177 | if (memcmp (buf, linux_rt_sigtramp_code, LINUX_RT_SIGTRAMP_LEN) != 0) |
| 178 | return 0; |
| 179 | |
| 180 | return pc; |
| 181 | } |
| 182 | |
| 183 | /* Return whether PC is in a Linux sigtramp routine. */ |
| 184 | |
| 185 | int |
| 186 | i386_linux_in_sigtramp (CORE_ADDR pc, char *name) |
| 187 | { |
| 188 | if (name) |
| 189 | return STREQ ("__restore", name) || STREQ ("__restore_rt", name); |
| 190 | |
| 191 | return (i386_linux_sigtramp_start (pc) != 0 |
| 192 | || i386_linux_rt_sigtramp_start (pc) != 0); |
| 193 | } |
| 194 | |
| 195 | /* Assuming FRAME is for a Linux sigtramp routine, return the address |
| 196 | of the associated sigcontext structure. */ |
| 197 | |
| 198 | CORE_ADDR |
| 199 | i386_linux_sigcontext_addr (struct frame_info *frame) |
| 200 | { |
| 201 | CORE_ADDR pc; |
| 202 | |
| 203 | pc = i386_linux_sigtramp_start (frame->pc); |
| 204 | if (pc) |
| 205 | { |
| 206 | CORE_ADDR sp; |
| 207 | |
| 208 | if (frame->next) |
| 209 | /* If this isn't the top frame, the next frame must be for the |
| 210 | signal handler itself. The sigcontext structure lives on |
| 211 | the stack, right after the signum argument. */ |
| 212 | return frame->next->frame + 12; |
| 213 | |
| 214 | /* This is the top frame. We'll have to find the address of the |
| 215 | sigcontext structure by looking at the stack pointer. Keep |
| 216 | in mind that the first instruction of the sigtramp code is |
| 217 | "pop %eax". If the PC is at this instruction, adjust the |
| 218 | returned value accordingly. */ |
| 219 | sp = read_register (SP_REGNUM); |
| 220 | if (pc == frame->pc) |
| 221 | return sp + 4; |
| 222 | return sp; |
| 223 | } |
| 224 | |
| 225 | pc = i386_linux_rt_sigtramp_start (frame->pc); |
| 226 | if (pc) |
| 227 | { |
| 228 | if (frame->next) |
| 229 | /* If this isn't the top frame, the next frame must be for the |
| 230 | signal handler itself. The sigcontext structure is part of |
| 231 | the user context. A pointer to the user context is passed |
| 232 | as the third argument to the signal handler. */ |
| 233 | return read_memory_integer (frame->next->frame + 16, 4) + 20; |
| 234 | |
| 235 | /* This is the top frame. Again, use the stack pointer to find |
| 236 | the address of the sigcontext structure. */ |
| 237 | return read_memory_integer (read_register (SP_REGNUM) + 8, 4) + 20; |
| 238 | } |
| 239 | |
| 240 | error ("Couldn't recognize signal trampoline."); |
| 241 | return 0; |
| 242 | } |
| 243 | |
| 244 | /* Offset to saved PC in sigcontext, from <asm/sigcontext.h>. */ |
| 245 | #define LINUX_SIGCONTEXT_PC_OFFSET (56) |
| 246 | |
| 247 | /* Assuming FRAME is for a Linux sigtramp routine, return the saved |
| 248 | program counter. */ |
| 249 | |
| 250 | CORE_ADDR |
| 251 | i386_linux_sigtramp_saved_pc (struct frame_info *frame) |
| 252 | { |
| 253 | CORE_ADDR addr; |
| 254 | addr = i386_linux_sigcontext_addr (frame); |
| 255 | return read_memory_integer (addr + LINUX_SIGCONTEXT_PC_OFFSET, 4); |
| 256 | } |
| 257 | |
| 258 | /* Offset to saved SP in sigcontext, from <asm/sigcontext.h>. */ |
| 259 | #define LINUX_SIGCONTEXT_SP_OFFSET (28) |
| 260 | |
| 261 | /* Assuming FRAME is for a Linux sigtramp routine, return the saved |
| 262 | stack pointer. */ |
| 263 | |
| 264 | CORE_ADDR |
| 265 | i386_linux_sigtramp_saved_sp (struct frame_info *frame) |
| 266 | { |
| 267 | CORE_ADDR addr; |
| 268 | addr = i386_linux_sigcontext_addr (frame); |
| 269 | return read_memory_integer (addr + LINUX_SIGCONTEXT_SP_OFFSET, 4); |
| 270 | } |
| 271 | |
| 272 | /* Immediately after a function call, return the saved pc. */ |
| 273 | |
| 274 | CORE_ADDR |
| 275 | i386_linux_saved_pc_after_call (struct frame_info *frame) |
| 276 | { |
| 277 | if (frame->signal_handler_caller) |
| 278 | return i386_linux_sigtramp_saved_pc (frame); |
| 279 | |
| 280 | return read_memory_integer (read_register (SP_REGNUM), 4); |
| 281 | } |