471 lines
15 KiB
C
471 lines
15 KiB
C
/* Target-dependent code for GNU/Linux running on i386's, for GDB.
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Copyright 2000, 2001, 2002 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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#include "regcache.h"
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#include "inferior.h"
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/* For i386_linux_skip_solib_resolver. */
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#include "symtab.h"
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#include "symfile.h"
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#include "objfiles.h"
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#include "solib-svr4.h" /* For struct link_map_offsets. */
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#include "i386-tdep.h"
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#include "i386-linux-tdep.h"
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/* Return the name of register REG. */
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static const char *
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i386_linux_register_name (int reg)
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{
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/* Deal with the extra "orig_eax" pseudo register. */
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if (reg == I386_LINUX_ORIG_EAX_REGNUM)
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return "orig_eax";
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return i386_register_name (reg);
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}
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/* Recognizing signal handler frames. */
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/* GNU/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 GNU/Linux will support SA_SIGINFO
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for 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 PC_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 GNU/Linux sigtramp routine. */
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static int
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i386_linux_pc_in_sigtramp (CORE_ADDR pc, char *name)
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{
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/* If we have NAME, we can optimize the search. The trampolines are
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named __restore and __restore_rt. However, they aren't dynamically
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exported from the shared C library, so the trampoline may appear to
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be part of the preceding function. This should always be sigaction,
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__sigaction, or __libc_sigaction (all aliases to the same function). */
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if (name == NULL || strstr (name, "sigaction") != NULL)
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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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return (strcmp ("__restore", name) == 0
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|| strcmp ("__restore_rt", name) == 0);
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}
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/* Assuming FRAME is for a GNU/Linux sigtramp routine, return the
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address of the associated sigcontext structure. */
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static 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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/* Set the program counter for process PTID to PC. */
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static void
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i386_linux_write_pc (CORE_ADDR pc, ptid_t ptid)
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{
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write_register_pid (PC_REGNUM, pc, ptid);
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/* We must be careful with modifying the program counter. If we
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just interrupted a system call, the kernel might try to restart
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it when we resume the inferior. On restarting the system call,
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the kernel will try backing up the program counter even though it
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no longer points at the system call. This typically results in a
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SIGSEGV or SIGILL. We can prevent this by writing `-1' in the
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"orig_eax" pseudo-register.
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Note that "orig_eax" is saved when setting up a dummy call frame.
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This means that it is properly restored when that frame is
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popped, and that the interrupted system call will be restarted
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when we resume the inferior on return from a function call from
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within GDB. In all other cases the system call will not be
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restarted. */
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write_register_pid (I386_LINUX_ORIG_EAX_REGNUM, -1, ptid);
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}
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/* Calling functions in shared libraries. */
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/* Find the minimal symbol named NAME, and return both the minsym
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struct and its objfile. This probably ought to be in minsym.c, but
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everything there is trying to deal with things like C++ and
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SOFUN_ADDRESS_MAYBE_TURQUOISE, ... Since this is so simple, it may
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be considered too special-purpose for general consumption. */
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static struct minimal_symbol *
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find_minsym_and_objfile (char *name, struct objfile **objfile_p)
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{
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struct objfile *objfile;
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ALL_OBJFILES (objfile)
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{
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struct minimal_symbol *msym;
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ALL_OBJFILE_MSYMBOLS (objfile, msym)
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{
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if (SYMBOL_NAME (msym)
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&& STREQ (SYMBOL_NAME (msym), name))
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{
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*objfile_p = objfile;
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return msym;
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}
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}
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}
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return 0;
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}
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static CORE_ADDR
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skip_hurd_resolver (CORE_ADDR pc)
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{
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/* The HURD dynamic linker is part of the GNU C library, so many
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GNU/Linux distributions use it. (All ELF versions, as far as I
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know.) An unresolved PLT entry points to "_dl_runtime_resolve",
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which calls "fixup" to patch the PLT, and then passes control to
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the function.
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We look for the symbol `_dl_runtime_resolve', and find `fixup' in
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the same objfile. If we are at the entry point of `fixup', then
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we set a breakpoint at the return address (at the top of the
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stack), and continue.
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It's kind of gross to do all these checks every time we're
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called, since they don't change once the executable has gotten
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started. But this is only a temporary hack --- upcoming versions
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of GNU/Linux will provide a portable, efficient interface for
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debugging programs that use shared libraries. */
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struct objfile *objfile;
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struct minimal_symbol *resolver
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= find_minsym_and_objfile ("_dl_runtime_resolve", &objfile);
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if (resolver)
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{
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struct minimal_symbol *fixup
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= lookup_minimal_symbol ("fixup", NULL, objfile);
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if (fixup && SYMBOL_VALUE_ADDRESS (fixup) == pc)
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return (SAVED_PC_AFTER_CALL (get_current_frame ()));
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}
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return 0;
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}
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/* See the comments for SKIP_SOLIB_RESOLVER at the top of infrun.c.
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This function:
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1) decides whether a PLT has sent us into the linker to resolve
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a function reference, and
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2) if so, tells us where to set a temporary breakpoint that will
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trigger when the dynamic linker is done. */
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CORE_ADDR
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i386_linux_skip_solib_resolver (CORE_ADDR pc)
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{
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CORE_ADDR result;
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/* Plug in functions for other kinds of resolvers here. */
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result = skip_hurd_resolver (pc);
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if (result)
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return result;
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return 0;
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}
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/* Fetch (and possibly build) an appropriate link_map_offsets
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structure for native GNU/Linux x86 targets using the struct offsets
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defined in link.h (but without actual reference to that file).
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This makes it possible to access GNU/Linux x86 shared libraries
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from a GDB that was not built on an GNU/Linux x86 host (for cross
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debugging). */
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static struct link_map_offsets *
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i386_linux_svr4_fetch_link_map_offsets (void)
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{
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static struct link_map_offsets lmo;
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static struct link_map_offsets *lmp = NULL;
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if (lmp == NULL)
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{
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lmp = &lmo;
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lmo.r_debug_size = 8; /* The actual size is 20 bytes, but
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this is all we need. */
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lmo.r_map_offset = 4;
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lmo.r_map_size = 4;
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lmo.link_map_size = 20; /* The actual size is 552 bytes, but
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this is all we need. */
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lmo.l_addr_offset = 0;
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lmo.l_addr_size = 4;
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lmo.l_name_offset = 4;
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lmo.l_name_size = 4;
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lmo.l_next_offset = 12;
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lmo.l_next_size = 4;
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lmo.l_prev_offset = 16;
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lmo.l_prev_size = 4;
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}
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return lmp;
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}
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static void
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i386_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
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{
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struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
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/* GNU/Linux uses ELF. */
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i386_elf_init_abi (info, gdbarch);
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/* We support the SSE registers on GNU/Linux. */
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tdep->num_xmm_regs = I386_NUM_XREGS - 1;
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/* set_gdbarch_num_regs (gdbarch, I386_SSE_NUM_REGS); */
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/* Since we have the extra "orig_eax" register on GNU/Linux, we have
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to adjust a few things. */
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set_gdbarch_write_pc (gdbarch, i386_linux_write_pc);
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set_gdbarch_num_regs (gdbarch, I386_SSE_NUM_REGS + 1);
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set_gdbarch_register_name (gdbarch, i386_linux_register_name);
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set_gdbarch_register_bytes (gdbarch, I386_SSE_SIZEOF_REGS + 4);
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tdep->jb_pc_offset = 20; /* From <bits/setjmp.h>. */
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tdep->sigcontext_addr = i386_linux_sigcontext_addr;
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tdep->sc_pc_offset = 14 * 4; /* From <asm/sigcontext.h>. */
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tdep->sc_sp_offset = 7 * 4;
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/* When the i386 Linux kernel calls a signal handler, the return
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address points to a bit of code on the stack. This function is
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used to identify this bit of code as a signal trampoline in order
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to support backtracing through calls to signal handlers. */
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set_gdbarch_pc_in_sigtramp (gdbarch, i386_linux_pc_in_sigtramp);
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set_solib_svr4_fetch_link_map_offsets (gdbarch,
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i386_linux_svr4_fetch_link_map_offsets);
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}
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/* Provide a prototype to silence -Wmissing-prototypes. */
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extern void _initialize_i386_linux_tdep (void);
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void
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_initialize_i386_linux_tdep (void)
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{
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gdbarch_register_osabi (bfd_arch_i386, GDB_OSABI_LINUX,
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i386_linux_init_abi);
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}
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