| /* Target-dependent code for Linux running on i386's, for GDB. |
| Copyright (C) 2000 Free Software Foundation, Inc. |
| |
| This file is part of GDB. |
| |
| This program is free software; you can redistribute it and/or modify |
| it under the terms of the GNU General Public License as published by |
| the Free Software Foundation; either version 2 of the License, or |
| (at your option) any later version. |
| |
| This program is distributed in the hope that it will be useful, |
| but WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| GNU General Public License for more details. |
| |
| You should have received a copy of the GNU General Public License |
| along with this program; if not, write to the Free Software |
| Foundation, Inc., 59 Temple Place - Suite 330, |
| Boston, MA 02111-1307, USA. */ |
| |
| #include "defs.h" |
| #include "gdbcore.h" |
| #include "frame.h" |
| #include "value.h" |
| |
| |
| /* Recognizing signal handler frames. */ |
| |
| /* Linux has two flavors of signals. Normal signal handlers, and |
| "realtime" (RT) signals. The RT signals can provide additional |
| information to the signal handler if the SA_SIGINFO flag is set |
| when establishing a signal handler using `sigaction'. It is not |
| unlikely that future versions of Linux will support SA_SIGINFO for |
| normal signals too. */ |
| |
| /* When the i386 Linux kernel calls a signal handler and the |
| SA_RESTORER flag isn't set, the return address points to a bit of |
| code on the stack. This function returns whether the PC appears to |
| be within this bit of code. |
| |
| The instruction sequence for normal signals is |
| pop %eax |
| mov $0x77,%eax |
| int $0x80 |
| or 0x58 0xb8 0x77 0x00 0x00 0x00 0xcd 0x80. |
| |
| Checking for the code sequence should be somewhat reliable, because |
| the effect is to call the system call sigreturn. This is unlikely |
| to occur anywhere other than a signal trampoline. |
| |
| It kind of sucks that we have to read memory from the process in |
| order to identify a signal trampoline, but there doesn't seem to be |
| any other way. The IN_SIGTRAMP macro in tm-linux.h arranges to |
| only call us if no function name could be identified, which should |
| be the case since the code is on the stack. |
| |
| Detection of signal trampolines for handlers that set the |
| SA_RESTORER flag is in general not possible. Unfortunately this is |
| what the GNU C Library has been doing for quite some time now. |
| However, as of version 2.1.2, the GNU C Library uses signal |
| trampolines (named __restore and __restore_rt) that are identical |
| to the ones used by the kernel. Therefore, these trampolines are |
| supported too. */ |
| |
| #define LINUX_SIGTRAMP_INSN0 (0x58) /* pop %eax */ |
| #define LINUX_SIGTRAMP_OFFSET0 (0) |
| #define LINUX_SIGTRAMP_INSN1 (0xb8) /* mov $NNNN,%eax */ |
| #define LINUX_SIGTRAMP_OFFSET1 (1) |
| #define LINUX_SIGTRAMP_INSN2 (0xcd) /* int */ |
| #define LINUX_SIGTRAMP_OFFSET2 (6) |
| |
| static const unsigned char linux_sigtramp_code[] = |
| { |
| LINUX_SIGTRAMP_INSN0, /* pop %eax */ |
| LINUX_SIGTRAMP_INSN1, 0x77, 0x00, 0x00, 0x00, /* mov $0x77,%eax */ |
| LINUX_SIGTRAMP_INSN2, 0x80 /* int $0x80 */ |
| }; |
| |
| #define LINUX_SIGTRAMP_LEN (sizeof linux_sigtramp_code) |
| |
| /* If PC is in a sigtramp routine, return the address of the start of |
| the routine. Otherwise, return 0. */ |
| |
| static CORE_ADDR |
| i386_linux_sigtramp_start (CORE_ADDR pc) |
| { |
| unsigned char buf[LINUX_SIGTRAMP_LEN]; |
| |
| /* We only recognize a signal trampoline if PC is at the start of |
| one of the three instructions. We optimize for finding the PC at |
| the start, as will be the case when the trampoline is not the |
| first frame on the stack. We assume that in the case where the |
| PC is not at the start of the instruction sequence, there will be |
| a few trailing readable bytes on the stack. */ |
| |
| if (read_memory_nobpt (pc, (char *) buf, LINUX_SIGTRAMP_LEN) != 0) |
| return 0; |
| |
| if (buf[0] != LINUX_SIGTRAMP_INSN0) |
| { |
| int adjust; |
| |
| switch (buf[0]) |
| { |
| case LINUX_SIGTRAMP_INSN1: |
| adjust = LINUX_SIGTRAMP_OFFSET1; |
| break; |
| case LINUX_SIGTRAMP_INSN2: |
| adjust = LINUX_SIGTRAMP_OFFSET2; |
| break; |
| default: |
| return 0; |
| } |
| |
| pc -= adjust; |
| |
| if (read_memory_nobpt (pc, (char *) buf, LINUX_SIGTRAMP_LEN) != 0) |
| return 0; |
| } |
| |
| if (memcmp (buf, linux_sigtramp_code, LINUX_SIGTRAMP_LEN) != 0) |
| return 0; |
| |
| return pc; |
| } |
| |
| /* This function does the same for RT signals. Here the instruction |
| sequence is |
| mov $0xad,%eax |
| int $0x80 |
| or 0xb8 0xad 0x00 0x00 0x00 0xcd 0x80. |
| |
| The effect is to call the system call rt_sigreturn. */ |
| |
| #define LINUX_RT_SIGTRAMP_INSN0 (0xb8) /* mov $NNNN,%eax */ |
| #define LINUX_RT_SIGTRAMP_OFFSET0 (0) |
| #define LINUX_RT_SIGTRAMP_INSN1 (0xcd) /* int */ |
| #define LINUX_RT_SIGTRAMP_OFFSET1 (5) |
| |
| static const unsigned char linux_rt_sigtramp_code[] = |
| { |
| LINUX_RT_SIGTRAMP_INSN0, 0xad, 0x00, 0x00, 0x00, /* mov $0xad,%eax */ |
| LINUX_RT_SIGTRAMP_INSN1, 0x80 /* int $0x80 */ |
| }; |
| |
| #define LINUX_RT_SIGTRAMP_LEN (sizeof linux_rt_sigtramp_code) |
| |
| /* If PC is in a RT sigtramp routine, return the address of the start |
| of the routine. Otherwise, return 0. */ |
| |
| static CORE_ADDR |
| i386_linux_rt_sigtramp_start (CORE_ADDR pc) |
| { |
| unsigned char buf[LINUX_RT_SIGTRAMP_LEN]; |
| |
| /* We only recognize a signal trampoline if PC is at the start of |
| one of the two instructions. We optimize for finding the PC at |
| the start, as will be the case when the trampoline is not the |
| first frame on the stack. We assume that in the case where the |
| PC is not at the start of the instruction sequence, there will be |
| a few trailing readable bytes on the stack. */ |
| |
| if (read_memory_nobpt (pc, (char *) buf, LINUX_RT_SIGTRAMP_LEN) != 0) |
| return 0; |
| |
| if (buf[0] != LINUX_RT_SIGTRAMP_INSN0) |
| { |
| if (buf[0] != LINUX_RT_SIGTRAMP_INSN1) |
| return 0; |
| |
| pc -= LINUX_RT_SIGTRAMP_OFFSET1; |
| |
| if (read_memory_nobpt (pc, (char *) buf, LINUX_RT_SIGTRAMP_LEN) != 0) |
| return 0; |
| } |
| |
| if (memcmp (buf, linux_rt_sigtramp_code, LINUX_RT_SIGTRAMP_LEN) != 0) |
| return 0; |
| |
| return pc; |
| } |
| |
| /* Return whether PC is in a Linux sigtramp routine. */ |
| |
| int |
| i386_linux_in_sigtramp (CORE_ADDR pc, char *name) |
| { |
| if (name) |
| return STREQ ("__restore", name) || STREQ ("__restore_rt", name); |
| |
| return (i386_linux_sigtramp_start (pc) != 0 |
| || i386_linux_rt_sigtramp_start (pc) != 0); |
| } |
| |
| /* Assuming FRAME is for a Linux sigtramp routine, return the address |
| of the associated sigcontext structure. */ |
| |
| CORE_ADDR |
| i386_linux_sigcontext_addr (struct frame_info *frame) |
| { |
| CORE_ADDR pc; |
| |
| pc = i386_linux_sigtramp_start (frame->pc); |
| if (pc) |
| { |
| CORE_ADDR sp; |
| |
| if (frame->next) |
| /* If this isn't the top frame, the next frame must be for the |
| signal handler itself. The sigcontext structure lives on |
| the stack, right after the signum argument. */ |
| return frame->next->frame + 12; |
| |
| /* This is the top frame. We'll have to find the address of the |
| sigcontext structure by looking at the stack pointer. Keep |
| in mind that the first instruction of the sigtramp code is |
| "pop %eax". If the PC is at this instruction, adjust the |
| returned value accordingly. */ |
| sp = read_register (SP_REGNUM); |
| if (pc == frame->pc) |
| return sp + 4; |
| return sp; |
| } |
| |
| pc = i386_linux_rt_sigtramp_start (frame->pc); |
| if (pc) |
| { |
| if (frame->next) |
| /* If this isn't the top frame, the next frame must be for the |
| signal handler itself. The sigcontext structure is part of |
| the user context. A pointer to the user context is passed |
| as the third argument to the signal handler. */ |
| return read_memory_integer (frame->next->frame + 16, 4) + 20; |
| |
| /* This is the top frame. Again, use the stack pointer to find |
| the address of the sigcontext structure. */ |
| return read_memory_integer (read_register (SP_REGNUM) + 8, 4) + 20; |
| } |
| |
| error ("Couldn't recognize signal trampoline."); |
| return 0; |
| } |
| |
| /* Offset to saved PC in sigcontext, from <asm/sigcontext.h>. */ |
| #define LINUX_SIGCONTEXT_PC_OFFSET (56) |
| |
| /* Assuming FRAME is for a Linux sigtramp routine, return the saved |
| program counter. */ |
| |
| CORE_ADDR |
| i386_linux_sigtramp_saved_pc (struct frame_info *frame) |
| { |
| CORE_ADDR addr; |
| addr = i386_linux_sigcontext_addr (frame); |
| return read_memory_integer (addr + LINUX_SIGCONTEXT_PC_OFFSET, 4); |
| } |
| |
| /* Offset to saved SP in sigcontext, from <asm/sigcontext.h>. */ |
| #define LINUX_SIGCONTEXT_SP_OFFSET (28) |
| |
| /* Assuming FRAME is for a Linux sigtramp routine, return the saved |
| stack pointer. */ |
| |
| CORE_ADDR |
| i386_linux_sigtramp_saved_sp (struct frame_info *frame) |
| { |
| CORE_ADDR addr; |
| addr = i386_linux_sigcontext_addr (frame); |
| return read_memory_integer (addr + LINUX_SIGCONTEXT_SP_OFFSET, 4); |
| } |
| |
| /* Immediately after a function call, return the saved pc. */ |
| |
| CORE_ADDR |
| i386_linux_saved_pc_after_call (struct frame_info *frame) |
| { |
| if (frame->signal_handler_caller) |
| return i386_linux_sigtramp_saved_pc (frame); |
| |
| return read_memory_integer (read_register (SP_REGNUM), 4); |
| } |