1 /* Displaced stepping related things.
3 Copyright (C) 2020-2023 Free Software Foundation, Inc.
5 This file is part of GDB.
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.
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.
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/>. */
21 #include "displaced-stepping.h"
23 #include "cli/cli-cmds.h"
27 #include "gdbthread.h"
30 #include "target/target.h"
32 /* Default destructor for displaced_step_copy_insn_closure. */
34 displaced_step_copy_insn_closure::~displaced_step_copy_insn_closure ()
37 bool debug_displaced
= false;
40 show_debug_displaced (struct ui_file
*file
, int from_tty
,
41 struct cmd_list_element
*c
, const char *value
)
43 gdb_printf (file
, _("Displace stepping debugging is %s.\n"), value
);
46 displaced_step_prepare_status
47 displaced_step_buffers::prepare (thread_info
*thread
, CORE_ADDR
&displaced_pc
)
49 gdb_assert (!thread
->displaced_step_state
.in_progress ());
51 /* Sanity check: the thread should not be using a buffer at this point. */
52 for (displaced_step_buffer
&buf
: m_buffers
)
53 gdb_assert (buf
.current_thread
!= thread
);
55 regcache
*regcache
= get_thread_regcache (thread
);
56 const address_space
*aspace
= regcache
->aspace ();
57 gdbarch
*arch
= regcache
->arch ();
58 ULONGEST len
= gdbarch_displaced_step_buffer_length (arch
);
60 /* Search for an unused buffer. */
61 displaced_step_buffer
*buffer
= nullptr;
62 displaced_step_prepare_status fail_status
63 = DISPLACED_STEP_PREPARE_STATUS_CANT
;
65 for (displaced_step_buffer
&candidate
: m_buffers
)
67 bool bp_in_range
= breakpoint_in_range_p (aspace
, candidate
.addr
, len
);
68 bool is_free
= candidate
.current_thread
== nullptr;
79 /* This buffer would be suitable, but it's used right now. */
80 fail_status
= DISPLACED_STEP_PREPARE_STATUS_UNAVAILABLE
;
85 /* There's a breakpoint set in the scratch pad location range
86 (which is usually around the entry point). We'd either
87 install it before resuming, which would overwrite/corrupt the
88 scratch pad, or if it was already inserted, this displaced
89 step would overwrite it. The latter is OK in the sense that
90 we already assume that no thread is going to execute the code
91 in the scratch pad range (after initial startup) anyway, but
92 the former is unacceptable. Simply punt and fallback to
93 stepping over this breakpoint in-line. */
94 displaced_debug_printf ("breakpoint set in displaced stepping "
95 "buffer at %s, can't use.",
96 paddress (arch
, candidate
.addr
));
100 if (buffer
== nullptr)
103 displaced_debug_printf ("selected buffer at %s",
104 paddress (arch
, buffer
->addr
));
106 /* Save the original PC of the thread. */
107 buffer
->original_pc
= regcache_read_pc (regcache
);
109 /* Return displaced step buffer address to caller. */
110 displaced_pc
= buffer
->addr
;
112 /* Save the original contents of the displaced stepping buffer. */
113 buffer
->saved_copy
.resize (len
);
115 int status
= target_read_memory (buffer
->addr
,
116 buffer
->saved_copy
.data (), len
);
118 throw_error (MEMORY_ERROR
,
119 _("Error accessing memory address %s (%s) for "
120 "displaced-stepping scratch space."),
121 paddress (arch
, buffer
->addr
), safe_strerror (status
));
123 displaced_debug_printf ("saved %s: %s",
124 paddress (arch
, buffer
->addr
),
125 bytes_to_string (buffer
->saved_copy
).c_str ());
127 /* Save this in a local variable first, so it's released if code below
129 displaced_step_copy_insn_closure_up copy_insn_closure
130 = gdbarch_displaced_step_copy_insn (arch
, buffer
->original_pc
,
131 buffer
->addr
, regcache
);
133 if (copy_insn_closure
== nullptr)
135 /* The architecture doesn't know how or want to displaced step
136 this instruction or instruction sequence. Fallback to
137 stepping over the breakpoint in-line. */
138 return DISPLACED_STEP_PREPARE_STATUS_CANT
;
141 /* This marks the buffer as being in use. */
142 buffer
->current_thread
= thread
;
144 /* Save this, now that we know everything went fine. */
145 buffer
->copy_insn_closure
= std::move (copy_insn_closure
);
147 /* Reset the displaced step buffer state if we failed to write PC.
148 Otherwise we will prevent this buffer from being used, as it will
149 always have a thread in buffer->current_thread. */
150 auto reset_buffer
= make_scope_exit
153 buffer
->current_thread
= nullptr;
154 buffer
->copy_insn_closure
.reset ();
157 /* Adjust the PC so it points to the displaced step buffer address that will
158 be used. This needs to be done after we save the copy_insn_closure, as
159 some architectures (Arm, for one) need that information so they can adjust
160 other data as needed. In particular, Arm needs to know if the instruction
161 being executed in the displaced step buffer is thumb or not. Without that
162 information, things will be very wrong in a random way. */
163 regcache_write_pc (regcache
, buffer
->addr
);
165 /* PC update successful. Discard the displaced step state rollback. */
166 reset_buffer
.release ();
168 /* Tell infrun not to try preparing a displaced step again for this inferior if
169 all buffers are taken. */
170 thread
->inf
->displaced_step_state
.unavailable
= true;
171 for (const displaced_step_buffer
&buf
: m_buffers
)
173 if (buf
.current_thread
== nullptr)
175 thread
->inf
->displaced_step_state
.unavailable
= false;
180 return DISPLACED_STEP_PREPARE_STATUS_OK
;
184 write_memory_ptid (ptid_t ptid
, CORE_ADDR memaddr
,
185 const gdb_byte
*myaddr
, int len
)
187 scoped_restore save_inferior_ptid
= make_scoped_restore (&inferior_ptid
);
189 inferior_ptid
= ptid
;
190 write_memory (memaddr
, myaddr
, len
);
194 displaced_step_instruction_executed_successfully
195 (gdbarch
*arch
, const target_waitstatus
&status
)
197 if (status
.kind () == TARGET_WAITKIND_STOPPED
198 && status
.sig () != GDB_SIGNAL_TRAP
)
201 /* All other (thread event) waitkinds can only happen if the
202 instruction fully executed. For example, a fork, or a syscall
203 entry can only happen if the syscall instruction actually
206 if (target_stopped_by_watchpoint ())
208 if (gdbarch_have_nonsteppable_watchpoint (arch
)
209 || target_have_steppable_watchpoint ())
216 displaced_step_finish_status
217 displaced_step_buffers::finish (gdbarch
*arch
, thread_info
*thread
,
218 const target_waitstatus
&status
)
220 gdb_assert (thread
->displaced_step_state
.in_progress ());
222 /* Find the buffer this thread was using. */
223 displaced_step_buffer
*buffer
= nullptr;
225 for (displaced_step_buffer
&candidate
: m_buffers
)
227 if (candidate
.current_thread
== thread
)
234 gdb_assert (buffer
!= nullptr);
236 /* Move this to a local variable so it's released in case something goes
238 displaced_step_copy_insn_closure_up copy_insn_closure
239 = std::move (buffer
->copy_insn_closure
);
240 gdb_assert (copy_insn_closure
!= nullptr);
242 /* Reset BUFFER->CURRENT_THREAD immediately to mark the buffer as available,
243 in case something goes wrong below. */
244 buffer
->current_thread
= nullptr;
246 /* Now that a buffer gets freed, tell infrun it can ask us to prepare a displaced
247 step again for this inferior. Do that here in case something goes wrong
249 thread
->inf
->displaced_step_state
.unavailable
= false;
251 ULONGEST len
= gdbarch_displaced_step_buffer_length (arch
);
253 /* Restore memory of the buffer. */
254 write_memory_ptid (thread
->ptid
, buffer
->addr
,
255 buffer
->saved_copy
.data (), len
);
257 displaced_debug_printf ("restored %s %s",
258 thread
->ptid
.to_string ().c_str (),
259 paddress (arch
, buffer
->addr
));
261 regcache
*rc
= get_thread_regcache (thread
);
263 bool instruction_executed_successfully
264 = displaced_step_instruction_executed_successfully (arch
, status
);
266 gdbarch_displaced_step_fixup (arch
, copy_insn_closure
.get (),
267 buffer
->original_pc
, buffer
->addr
,
268 rc
, instruction_executed_successfully
);
270 return (instruction_executed_successfully
271 ? DISPLACED_STEP_FINISH_STATUS_OK
272 : DISPLACED_STEP_FINISH_STATUS_NOT_EXECUTED
);
275 const displaced_step_copy_insn_closure
*
276 displaced_step_buffers::copy_insn_closure_by_addr (CORE_ADDR addr
)
278 for (const displaced_step_buffer
&buffer
: m_buffers
)
280 /* Make sure we have active buffers to compare to. */
281 if (buffer
.current_thread
!= nullptr && addr
== buffer
.addr
)
283 /* The closure information should always be available. */
284 gdb_assert (buffer
.copy_insn_closure
.get () != nullptr);
285 return buffer
.copy_insn_closure
.get ();
293 displaced_step_buffers::restore_in_ptid (ptid_t ptid
)
295 for (const displaced_step_buffer
&buffer
: m_buffers
)
297 if (buffer
.current_thread
== nullptr)
300 regcache
*regcache
= get_thread_regcache (buffer
.current_thread
);
301 gdbarch
*arch
= regcache
->arch ();
302 ULONGEST len
= gdbarch_displaced_step_buffer_length (arch
);
304 write_memory_ptid (ptid
, buffer
.addr
, buffer
.saved_copy
.data (), len
);
306 displaced_debug_printf ("restored in ptid %s %s",
307 ptid
.to_string ().c_str (),
308 paddress (arch
, buffer
.addr
));
312 void _initialize_displaced_stepping ();
314 _initialize_displaced_stepping ()
316 add_setshow_boolean_cmd ("displaced", class_maintenance
,
317 &debug_displaced
, _("\
318 Set displaced stepping debugging."), _("\
319 Show displaced stepping debugging."), _("\
320 When non-zero, displaced stepping specific debugging is enabled."),
322 show_debug_displaced
,
323 &setdebuglist
, &showdebuglist
);