gdb/displaced-stepping.c

   1 /* Displaced stepping related things.
   2
   3    Copyright (C) 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 "defs.h"
  21 #include "displaced-stepping.h"
  22
  23 #include "cli/cli-cmds.h"
  24 #include "command.h"
  25 #include "gdbarch.h"
  26 #include "gdbcore.h"
  27 #include "gdbthread.h"
  28 #include "inferior.h"
  29 #include "regcache.h"
  30 #include "target/target.h"
  31
  32 /* Default destructor for displaced_step_copy_insn_closure.  */
  33
  34 displaced_step_copy_insn_closure::~displaced_step_copy_insn_closure ()
  35   = default;
  36
  37 bool debug_displaced = false;
  38
  39 static void
  40 show_debug_displaced (struct ui_file *file, int from_tty,
  41                       struct cmd_list_element *c, const char *value)
  42 {
  43   fprintf_filtered (file, _("Displace stepping debugging is %s.\n"), value);
  44 }
  45
  46 displaced_step_prepare_status
  47 displaced_step_buffer::prepare (thread_info *thread, CORE_ADDR &displaced_pc)
  48 {
  49   gdb_assert (!thread->displaced_step_state.in_progress ());
  50
  51   /* Is a thread currently using the buffer?  */
  52   if (m_current_thread != nullptr)
  53     {
  54       /* If so, it better not be this thread.  */
  55       gdb_assert (thread != m_current_thread);
  56       return DISPLACED_STEP_PREPARE_STATUS_UNAVAILABLE;
  57     }
  58
  59   regcache *regcache = get_thread_regcache (thread);
  60   const address_space *aspace = regcache->aspace ();
  61   gdbarch *arch = regcache->arch ();
  62   ULONGEST len = gdbarch_max_insn_length (arch);
  63
  64   if (breakpoint_in_range_p (aspace, m_addr, len))
  65     {
  66       /* There's a breakpoint set in the scratch pad location range
  67          (which is usually around the entry point).  We'd either
  68          install it before resuming, which would overwrite/corrupt the
  69          scratch pad, or if it was already inserted, this displaced
  70          step would overwrite it.  The latter is OK in the sense that
  71          we already assume that no thread is going to execute the code
  72          in the scratch pad range (after initial startup) anyway, but
  73          the former is unacceptable.  Simply punt and fallback to
  74          stepping over this breakpoint in-line.  */
  75       displaced_debug_printf ("breakpoint set in scratch pad.  "
  76                               "Stepping over breakpoint in-line instead.");
  77
  78       return DISPLACED_STEP_PREPARE_STATUS_CANT;
  79     }
  80
  81   m_original_pc = regcache_read_pc (regcache);
  82   displaced_pc = m_addr;
  83
  84   /* Save the original contents of the displaced stepping buffer.  */
  85   m_saved_copy.resize (len);
  86
  87   int status = target_read_memory (m_addr, m_saved_copy.data (), len);
  88   if (status != 0)
  89     throw_error (MEMORY_ERROR,
  90                  _("Error accessing memory address %s (%s) for "
  91                    "displaced-stepping scratch space."),
  92                  paddress (arch, m_addr), safe_strerror (status));
  93
  94   displaced_debug_printf ("saved %s: %s",
  95                           paddress (arch, m_addr),
  96                           displaced_step_dump_bytes
  97                             (m_saved_copy.data (), len).c_str ());
  98
  99   /* Save this in a local variable first, so it's released if code below
 100      throws.  */
 101   displaced_step_copy_insn_closure_up copy_insn_closure
 102     = gdbarch_displaced_step_copy_insn (arch, m_original_pc, m_addr, regcache);
 103
 104   if (copy_insn_closure == nullptr)
 105     {
 106       /* The architecture doesn't know how or want to displaced step
 107         this instruction or instruction sequence.  Fallback to
 108         stepping over the breakpoint in-line.  */
 109       return DISPLACED_STEP_PREPARE_STATUS_CANT;
 110     }
 111
 112   /* Resume execution at the copy.  */
 113   regcache_write_pc (regcache, m_addr);
 114
 115   /* This marks the buffer as being in use.  */
 116   m_current_thread = thread;
 117
 118   /* Save this, now that we know everything went fine.  */
 119   m_copy_insn_closure = std::move (copy_insn_closure);
 120
 121   /* Tell infrun not to try preparing a displaced step again for this inferior.  */
 122   thread->inf->displaced_step_state.unavailable = true;
 123
 124   return DISPLACED_STEP_PREPARE_STATUS_OK;
 125 }
 126
 127 static void
 128 write_memory_ptid (ptid_t ptid, CORE_ADDR memaddr,
 129                    const gdb_byte *myaddr, int len)
 130 {
 131   scoped_restore save_inferior_ptid = make_scoped_restore (&inferior_ptid);
 132
 133   inferior_ptid = ptid;
 134   write_memory (memaddr, myaddr, len);
 135 }
 136
 137 static bool
 138 displaced_step_instruction_executed_successfully (gdbarch *arch,
 139                                                   gdb_signal signal)
 140 {
 141   if (signal != GDB_SIGNAL_TRAP)
 142     return false;
 143
 144   if (target_stopped_by_watchpoint ())
 145     {
 146       if (gdbarch_have_nonsteppable_watchpoint (arch)
 147           || target_have_steppable_watchpoint ())
 148         return false;
 149     }
 150
 151   return true;
 152 }
 153
 154 displaced_step_finish_status
 155 displaced_step_buffer::finish (gdbarch *arch, thread_info *thread,
 156                                gdb_signal sig)
 157 {
 158   gdb_assert (thread->displaced_step_state.in_progress ());
 159   gdb_assert (thread == m_current_thread);
 160
 161   /* Move this to a local variable so it's released in case something goes
 162      wrong.  */
 163   displaced_step_copy_insn_closure_up copy_insn_closure
 164     = std::move (m_copy_insn_closure);
 165   gdb_assert (copy_insn_closure != nullptr);
 166
 167   /* Reset M_CURRENT_THREAD immediately to mark the buffer as available, in case
 168      something goes wrong below.  */
 169   m_current_thread = nullptr;
 170
 171   /* Now that a buffer gets freed, tell infrun it can ask us to prepare a displaced
 172      step again for this inferior.  Do that here in case something goes wrong
 173      below.  */
 174   thread->inf->displaced_step_state.unavailable = false;
 175
 176   ULONGEST len = gdbarch_max_insn_length (arch);
 177
 178   write_memory_ptid (thread->ptid, m_addr,
 179                      m_saved_copy.data (), len);
 180
 181   displaced_debug_printf ("restored %s %s",
 182                           target_pid_to_str (thread->ptid).c_str (),
 183                           paddress (arch, m_addr));
 184
 185   regcache *rc = get_thread_regcache (thread);
 186
 187   bool instruction_executed_successfully
 188     = displaced_step_instruction_executed_successfully (arch, sig);
 189
 190   if (instruction_executed_successfully)
 191     {
 192       gdbarch_displaced_step_fixup (arch, copy_insn_closure.get (), m_original_pc,
 193                                     m_addr, rc);
 194       return DISPLACED_STEP_FINISH_STATUS_OK;
 195     }
 196   else
 197     {
 198       /* Since the instruction didn't complete, all we can do is relocate the
 199          PC.  */
 200       CORE_ADDR pc = regcache_read_pc (rc);
 201       pc = m_original_pc + (pc - m_addr);
 202       regcache_write_pc (rc, pc);
 203       return DISPLACED_STEP_FINISH_STATUS_NOT_EXECUTED;
 204     }
 205 }
 206
 207 const displaced_step_copy_insn_closure *
 208 displaced_step_buffer::copy_insn_closure_by_addr (CORE_ADDR addr)
 209 {
 210   if (addr == m_addr)
 211     return m_copy_insn_closure.get ();
 212   else
 213     return nullptr;
 214 }
 215
 216 void
 217 displaced_step_buffer::restore_in_ptid (ptid_t ptid)
 218 {
 219   if (m_current_thread != nullptr)
 220     {
 221       regcache *regcache = get_thread_regcache (m_current_thread);
 222       gdbarch *arch = regcache->arch ();
 223       ULONGEST len = gdbarch_max_insn_length (arch);
 224
 225       write_memory_ptid (ptid, m_addr, m_saved_copy.data (), len);
 226
 227       displaced_debug_printf ("restored in ptid %s %s",
 228                               target_pid_to_str (ptid).c_str (),
 229                               paddress (arch, m_addr));
 230     }
 231 }
 232
 233 void _initialize_displaced_stepping ();
 234 void
 235 _initialize_displaced_stepping ()
 236 {
 237   add_setshow_boolean_cmd ("displaced", class_maintenance,
 238                            &debug_displaced, _("\
 239 Set displaced stepping debugging."), _("\
 240 Show displaced stepping debugging."), _("\
 241 When non-zero, displaced stepping specific debugging is enabled."),
 242                             NULL,
 243                             show_debug_displaced,
 244                             &setdebuglist, &showdebuglist);
 245 }