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