1/* Low-level debug register code for GNU/Linux x86 (i386 and x86-64).
2
3   Copyright (C) 1999-2020 Free Software Foundation, Inc.
4
5   This file is part of GDB.
6
7   This program is free software; you can redistribute it and/or modify
8   it under the terms of the GNU General Public License as published by
9   the Free Software Foundation; either version 3 of the License, or
10   (at your option) any later version.
11
12   This program is distributed in the hope that it will be useful,
13   but WITHOUT ANY WARRANTY; without even the implied warranty of
14   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
15   GNU General Public License for more details.
16
17   You should have received a copy of the GNU General Public License
18   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
19
20#include "gdbsupport/common-defs.h"
21#include "nat/gdb_ptrace.h"
22#include <sys/user.h>
23#include "target/waitstatus.h"
24#include "nat/x86-linux.h"
25#include "nat/x86-dregs.h"
26#include "nat/x86-linux-dregs.h"
27
28/* Return the offset of REGNUM in the u_debugreg field of struct
29   user.  */
30
31static int
32u_debugreg_offset (int regnum)
33{
34  return (offsetof (struct user, u_debugreg)
35	  + sizeof (((struct user *) 0)->u_debugreg[0]) * regnum);
36}
37
38/* Get debug register REGNUM value from the LWP specified by PTID.  */
39
40static unsigned long
41x86_linux_dr_get (ptid_t ptid, int regnum)
42{
43  int tid;
44  unsigned long value;
45
46  gdb_assert (ptid.lwp_p ());
47  tid = ptid.lwp ();
48
49  errno = 0;
50  value = ptrace (PTRACE_PEEKUSER, tid, u_debugreg_offset (regnum), 0);
51  if (errno != 0)
52    perror_with_name (_("Couldn't read debug register"));
53
54  return value;
55}
56
57/* Set debug register REGNUM to VALUE in the LWP specified by PTID.  */
58
59static void
60x86_linux_dr_set (ptid_t ptid, int regnum, unsigned long value)
61{
62  int tid;
63
64  gdb_assert (ptid.lwp_p ());
65  tid = ptid.lwp ();
66
67  errno = 0;
68  ptrace (PTRACE_POKEUSER, tid, u_debugreg_offset (regnum), value);
69  if (errno != 0)
70    perror_with_name (_("Couldn't write debug register"));
71}
72
73/* Callback for iterate_over_lwps.  Mark that our local mirror of
74   LWP's debug registers has been changed, and cause LWP to stop if
75   it isn't already.  Values are written from our local mirror to
76   the actual debug registers immediately prior to LWP resuming.  */
77
78static int
79update_debug_registers_callback (struct lwp_info *lwp)
80{
81  lwp_set_debug_registers_changed (lwp, 1);
82
83  if (!lwp_is_stopped (lwp))
84    linux_stop_lwp (lwp);
85
86  /* Continue the iteration.  */
87  return 0;
88}
89
90/* See nat/x86-linux-dregs.h.  */
91
92CORE_ADDR
93x86_linux_dr_get_addr (int regnum)
94{
95  gdb_assert (DR_FIRSTADDR <= regnum && regnum <= DR_LASTADDR);
96
97  return x86_linux_dr_get (current_lwp_ptid (), regnum);
98}
99
100/* See nat/x86-linux-dregs.h.  */
101
102void
103x86_linux_dr_set_addr (int regnum, CORE_ADDR addr)
104{
105  ptid_t pid_ptid = ptid_t (current_lwp_ptid ().pid ());
106
107  gdb_assert (DR_FIRSTADDR <= regnum && regnum <= DR_LASTADDR);
108
109  iterate_over_lwps (pid_ptid, update_debug_registers_callback);
110}
111
112/* See nat/x86-linux-dregs.h.  */
113
114unsigned long
115x86_linux_dr_get_control (void)
116{
117  return x86_linux_dr_get (current_lwp_ptid (), DR_CONTROL);
118}
119
120/* See nat/x86-linux-dregs.h.  */
121
122void
123x86_linux_dr_set_control (unsigned long control)
124{
125  ptid_t pid_ptid = ptid_t (current_lwp_ptid ().pid ());
126
127  iterate_over_lwps (pid_ptid, update_debug_registers_callback);
128}
129
130/* See nat/x86-linux-dregs.h.  */
131
132unsigned long
133x86_linux_dr_get_status (void)
134{
135  return x86_linux_dr_get (current_lwp_ptid (), DR_STATUS);
136}
137
138/* See nat/x86-linux-dregs.h.  */
139
140void
141x86_linux_update_debug_registers (struct lwp_info *lwp)
142{
143  ptid_t ptid = ptid_of_lwp (lwp);
144  int clear_status = 0;
145
146  gdb_assert (lwp_is_stopped (lwp));
147
148  if (lwp_debug_registers_changed (lwp))
149    {
150      struct x86_debug_reg_state *state
151	= x86_debug_reg_state (ptid.pid ());
152      int i;
153
154      /* Prior to Linux kernel 2.6.33 commit
155	 72f674d203cd230426437cdcf7dd6f681dad8b0d, setting DR0-3 to
156	 a value that did not match what was enabled in DR_CONTROL
157	 resulted in EINVAL.  To avoid this we zero DR_CONTROL before
158	 writing address registers, only writing DR_CONTROL's actual
159	 value once all the addresses are in place.  */
160      x86_linux_dr_set (ptid, DR_CONTROL, 0);
161
162      ALL_DEBUG_ADDRESS_REGISTERS (i)
163	if (state->dr_ref_count[i] > 0)
164	  {
165	    x86_linux_dr_set (ptid, i, state->dr_mirror[i]);
166
167	    /* If we're setting a watchpoint, any change the inferior
168	       has made to its debug registers needs to be discarded
169	       to avoid x86_stopped_data_address getting confused.  */
170	    clear_status = 1;
171	  }
172
173      /* If DR_CONTROL is supposed to be zero then it's already set.  */
174      if (state->dr_control_mirror != 0)
175	x86_linux_dr_set (ptid, DR_CONTROL, state->dr_control_mirror);
176
177      lwp_set_debug_registers_changed (lwp, 0);
178    }
179
180  if (clear_status
181      || lwp_stop_reason (lwp) == TARGET_STOPPED_BY_WATCHPOINT)
182    x86_linux_dr_set (ptid, DR_STATUS, 0);
183}
184