binutils-gdb/gdb/nat/x86-linux.c

/* Native-dependent code for GNU/Linux x86 (i386 and x86-64).

   Copyright (C) 1999-2025 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 3 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, see <http://www.gnu.org/licenses/>.  */

#include "elf/common.h"
#include "gdbsupport/common-defs.h"
#include "nat/gdb_ptrace.h"
#include "nat/linux-ptrace.h"
#include "nat/x86-cpuid.h"
#include <sys/uio.h>
#include "x86-linux.h"
#include "x86-linux-dregs.h"
#include "nat/gdb_ptrace.h"
#include <sys/user.h>

/* Per-thread arch-specific data we want to keep.  */

struct arch_lwp_info
{
  /* Non-zero if our copy differs from what's recorded in the
     thread.  */
  int debug_registers_changed;
};

/* See nat/x86-linux.h.  */

void
lwp_set_debug_registers_changed (struct lwp_info *lwp, int value)
{
  if (lwp_arch_private_info (lwp) == NULL)
    lwp_set_arch_private_info (lwp, XCNEW (struct arch_lwp_info));

  lwp_arch_private_info (lwp)->debug_registers_changed = value;
}

/* See nat/x86-linux.h.  */

int
lwp_debug_registers_changed (struct lwp_info *lwp)
{
  struct arch_lwp_info *info = lwp_arch_private_info (lwp);

  /* NULL means either that this is the main thread still going
     through the shell, or that no watchpoint has been set yet.
     The debug registers are unchanged in either case.  */
  if (info == NULL)
    return 0;

  return info->debug_registers_changed;
}

/* See nat/x86-linux.h.  */

void
x86_linux_new_thread (struct lwp_info *lwp)
{
  lwp_set_debug_registers_changed (lwp, 1);
}

/* See nat/x86-linux.h.  */

void
x86_linux_delete_thread (struct arch_lwp_info *arch_lwp)
{
  xfree (arch_lwp);
}

/* See nat/x86-linux.h.  */

void
x86_linux_prepare_to_resume (struct lwp_info *lwp)
{
  x86_linux_update_debug_registers (lwp);
}

#ifdef __x86_64__
/* Value of CS segment register:
     64bit process: 0x33
     32bit process: 0x23  */
#define AMD64_LINUX_USER64_CS 0x33

/* Value of DS segment register:
     LP64 process: 0x0
     X32 process: 0x2b  */
#define AMD64_LINUX_X32_DS 0x2b
#endif

/* See nat/x86-linux.h.  */

x86_linux_arch_size
x86_linux_ptrace_get_arch_size (int tid)
{
#ifdef __x86_64__
  unsigned long cs;
  unsigned long ds;

  /* Get CS register.  */
  errno = 0;
  cs = ptrace (PTRACE_PEEKUSER, tid,
	       offsetof (struct user_regs_struct, cs), 0);
  if (errno != 0)
    perror_with_name (_("Couldn't get CS register"));

  bool is_64bit = cs == AMD64_LINUX_USER64_CS;

  /* Get DS register.  */
  errno = 0;
  ds = ptrace (PTRACE_PEEKUSER, tid,
	       offsetof (struct user_regs_struct, ds), 0);
  if (errno != 0)
    perror_with_name (_("Couldn't get DS register"));

  bool is_x32 = ds == AMD64_LINUX_X32_DS;

  return x86_linux_arch_size (is_64bit, is_x32);
#else
  return x86_linux_arch_size (false, false);
#endif
}

/* See nat/x86-linux.h.  */

bool
x86_check_ssp_support (const int tid)
{
  /* It's not enough to check shadow stack support with the ptrace call
     below only, as we cannot distinguish between shadow stack not enabled
     for the current thread and shadow stack is not supported by HW.  In
     both scenarios the ptrace call fails with ENODEV.  In case shadow
     stack is not enabled for the current thread, we still want to return
     true.  */
  unsigned int eax, ebx, ecx, edx;
  eax = ebx = ecx = edx = 0;

  if (!__get_cpuid_count (7, 0, &eax, &ebx, &ecx, &edx))
    return false;

  if ((ecx & bit_SHSTK) == 0)
    return false;

  /* Further check for NT_X86_SHSTK kernel support.  */
  uint64_t ssp;
  iovec iov {&ssp, sizeof (ssp) };

  errno = 0;
  int res = ptrace (PTRACE_GETREGSET, tid, NT_X86_SHSTK, &iov);
  if (res < 0)
    {
      if (errno == EINVAL)
	{
	  /* The errno EINVAL for a PTRACE_GETREGSET call indicates that
	     kernel support is not available.  */
	  return false;
	}
      else if (errno == ENODEV)
	{
	  /* At this point, since we already checked CPUID, the errno
	     ENODEV for a PTRACE_GETREGSET call indicates that shadow
	     stack is not enabled for the current thread.  As it could be
	     enabled later, we still want to return true here.  */
	  return true;
	}
      else
	{
	  warning (_("Unknown ptrace error for NT_X86_SHSTK: %s"),
		   safe_strerror (errno));
	  return false;
	}
    }

  return true;
}