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c7acb87b SM |
1 | /* Displaced stepping related things. |
2 | ||
3666a048 | 3 | Copyright (C) 2020-2021 Free Software Foundation, Inc. |
c7acb87b SM |
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" | |
c7acb87b | 22 | |
187b041e | 23 | #include "cli/cli-cmds.h" |
c7acb87b | 24 | #include "command.h" |
187b041e SM |
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" | |
c7acb87b SM |
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 | ||
187b041e | 46 | displaced_step_prepare_status |
480af54c | 47 | displaced_step_buffers::prepare (thread_info *thread, CORE_ADDR &displaced_pc) |
187b041e SM |
48 | { |
49 | gdb_assert (!thread->displaced_step_state.in_progress ()); | |
50 | ||
480af54c SM |
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); | |
187b041e SM |
54 | |
55 | regcache *regcache = get_thread_regcache (thread); | |
56 | const address_space *aspace = regcache->aspace (); | |
57 | gdbarch *arch = regcache->arch (); | |
58 | ULONGEST len = gdbarch_max_insn_length (arch); | |
59 | ||
480af54c SM |
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; | |
187b041e | 64 | |
480af54c SM |
65 | for (displaced_step_buffer &candidate : m_buffers) |
66 | { | |
67 | bool bp_in_range = breakpoint_in_range_p (aspace, candidate.addr, len); | |
68 | bool is_free = candidate.current_thread == nullptr; | |
69 | ||
70 | if (!bp_in_range) | |
71 | { | |
72 | if (is_free) | |
73 | { | |
74 | buffer = &candidate; | |
75 | break; | |
76 | } | |
77 | else | |
78 | { | |
79 | /* This buffer would be suitable, but it's used right now. */ | |
80 | fail_status = DISPLACED_STEP_PREPARE_STATUS_UNAVAILABLE; | |
81 | } | |
82 | } | |
83 | else | |
84 | { | |
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)); | |
97 | } | |
187b041e SM |
98 | } |
99 | ||
480af54c SM |
100 | if (buffer == nullptr) |
101 | return fail_status; | |
102 | ||
103 | displaced_debug_printf ("selected buffer at %s", | |
104 | paddress (arch, buffer->addr)); | |
105 | ||
106 | /* Save the original PC of the thread. */ | |
107 | buffer->original_pc = regcache_read_pc (regcache); | |
108 | ||
109 | /* Return displaced step buffer address to caller. */ | |
110 | displaced_pc = buffer->addr; | |
187b041e SM |
111 | |
112 | /* Save the original contents of the displaced stepping buffer. */ | |
480af54c | 113 | buffer->saved_copy.resize (len); |
187b041e | 114 | |
480af54c SM |
115 | int status = target_read_memory (buffer->addr, |
116 | buffer->saved_copy.data (), len); | |
187b041e SM |
117 | if (status != 0) |
118 | throw_error (MEMORY_ERROR, | |
119 | _("Error accessing memory address %s (%s) for " | |
120 | "displaced-stepping scratch space."), | |
480af54c | 121 | paddress (arch, buffer->addr), safe_strerror (status)); |
187b041e SM |
122 | |
123 | displaced_debug_printf ("saved %s: %s", | |
480af54c | 124 | paddress (arch, buffer->addr), |
187b041e | 125 | displaced_step_dump_bytes |
480af54c | 126 | (buffer->saved_copy.data (), len).c_str ()); |
187b041e SM |
127 | |
128 | /* Save this in a local variable first, so it's released if code below | |
129 | throws. */ | |
130 | displaced_step_copy_insn_closure_up copy_insn_closure | |
480af54c SM |
131 | = gdbarch_displaced_step_copy_insn (arch, buffer->original_pc, |
132 | buffer->addr, regcache); | |
187b041e SM |
133 | |
134 | if (copy_insn_closure == nullptr) | |
135 | { | |
136 | /* The architecture doesn't know how or want to displaced step | |
480af54c SM |
137 | this instruction or instruction sequence. Fallback to |
138 | stepping over the breakpoint in-line. */ | |
187b041e SM |
139 | return DISPLACED_STEP_PREPARE_STATUS_CANT; |
140 | } | |
141 | ||
142 | /* Resume execution at the copy. */ | |
480af54c | 143 | regcache_write_pc (regcache, buffer->addr); |
187b041e SM |
144 | |
145 | /* This marks the buffer as being in use. */ | |
480af54c | 146 | buffer->current_thread = thread; |
187b041e SM |
147 | |
148 | /* Save this, now that we know everything went fine. */ | |
480af54c | 149 | buffer->copy_insn_closure = std::move (copy_insn_closure); |
187b041e | 150 | |
480af54c SM |
151 | /* Tell infrun not to try preparing a displaced step again for this inferior if |
152 | all buffers are taken. */ | |
187b041e | 153 | thread->inf->displaced_step_state.unavailable = true; |
480af54c SM |
154 | for (const displaced_step_buffer &buf : m_buffers) |
155 | { | |
156 | if (buf.current_thread == nullptr) | |
157 | { | |
158 | thread->inf->displaced_step_state.unavailable = false; | |
159 | break; | |
160 | } | |
161 | } | |
187b041e SM |
162 | |
163 | return DISPLACED_STEP_PREPARE_STATUS_OK; | |
164 | } | |
165 | ||
166 | static void | |
167 | write_memory_ptid (ptid_t ptid, CORE_ADDR memaddr, | |
168 | const gdb_byte *myaddr, int len) | |
169 | { | |
170 | scoped_restore save_inferior_ptid = make_scoped_restore (&inferior_ptid); | |
171 | ||
172 | inferior_ptid = ptid; | |
173 | write_memory (memaddr, myaddr, len); | |
174 | } | |
175 | ||
176 | static bool | |
177 | displaced_step_instruction_executed_successfully (gdbarch *arch, | |
178 | gdb_signal signal) | |
179 | { | |
180 | if (signal != GDB_SIGNAL_TRAP) | |
181 | return false; | |
182 | ||
183 | if (target_stopped_by_watchpoint ()) | |
184 | { | |
185 | if (gdbarch_have_nonsteppable_watchpoint (arch) | |
186 | || target_have_steppable_watchpoint ()) | |
187 | return false; | |
188 | } | |
189 | ||
190 | return true; | |
191 | } | |
192 | ||
193 | displaced_step_finish_status | |
480af54c SM |
194 | displaced_step_buffers::finish (gdbarch *arch, thread_info *thread, |
195 | gdb_signal sig) | |
187b041e SM |
196 | { |
197 | gdb_assert (thread->displaced_step_state.in_progress ()); | |
480af54c SM |
198 | |
199 | /* Find the buffer this thread was using. */ | |
200 | displaced_step_buffer *buffer = nullptr; | |
201 | ||
202 | for (displaced_step_buffer &candidate : m_buffers) | |
203 | { | |
204 | if (candidate.current_thread == thread) | |
205 | { | |
206 | buffer = &candidate; | |
207 | break; | |
208 | } | |
209 | } | |
210 | ||
211 | gdb_assert (buffer != nullptr); | |
187b041e SM |
212 | |
213 | /* Move this to a local variable so it's released in case something goes | |
214 | wrong. */ | |
215 | displaced_step_copy_insn_closure_up copy_insn_closure | |
480af54c | 216 | = std::move (buffer->copy_insn_closure); |
187b041e SM |
217 | gdb_assert (copy_insn_closure != nullptr); |
218 | ||
480af54c SM |
219 | /* Reset BUFFER->CURRENT_THREAD immediately to mark the buffer as available, |
220 | in case something goes wrong below. */ | |
221 | buffer->current_thread = nullptr; | |
187b041e SM |
222 | |
223 | /* Now that a buffer gets freed, tell infrun it can ask us to prepare a displaced | |
224 | step again for this inferior. Do that here in case something goes wrong | |
225 | below. */ | |
226 | thread->inf->displaced_step_state.unavailable = false; | |
227 | ||
228 | ULONGEST len = gdbarch_max_insn_length (arch); | |
229 | ||
480af54c SM |
230 | /* Restore memory of the buffer. */ |
231 | write_memory_ptid (thread->ptid, buffer->addr, | |
232 | buffer->saved_copy.data (), len); | |
187b041e SM |
233 | |
234 | displaced_debug_printf ("restored %s %s", | |
235 | target_pid_to_str (thread->ptid).c_str (), | |
480af54c | 236 | paddress (arch, buffer->addr)); |
187b041e SM |
237 | |
238 | regcache *rc = get_thread_regcache (thread); | |
239 | ||
240 | bool instruction_executed_successfully | |
241 | = displaced_step_instruction_executed_successfully (arch, sig); | |
242 | ||
243 | if (instruction_executed_successfully) | |
244 | { | |
480af54c SM |
245 | gdbarch_displaced_step_fixup (arch, copy_insn_closure.get (), |
246 | buffer->original_pc, | |
247 | buffer->addr, rc); | |
187b041e SM |
248 | return DISPLACED_STEP_FINISH_STATUS_OK; |
249 | } | |
250 | else | |
251 | { | |
252 | /* Since the instruction didn't complete, all we can do is relocate the | |
253 | PC. */ | |
254 | CORE_ADDR pc = regcache_read_pc (rc); | |
480af54c | 255 | pc = buffer->original_pc + (pc - buffer->addr); |
187b041e SM |
256 | regcache_write_pc (rc, pc); |
257 | return DISPLACED_STEP_FINISH_STATUS_NOT_EXECUTED; | |
258 | } | |
259 | } | |
260 | ||
261 | const displaced_step_copy_insn_closure * | |
480af54c | 262 | displaced_step_buffers::copy_insn_closure_by_addr (CORE_ADDR addr) |
187b041e | 263 | { |
480af54c SM |
264 | for (const displaced_step_buffer &buffer : m_buffers) |
265 | { | |
266 | if (addr == buffer.addr) | |
267 | return buffer.copy_insn_closure.get (); | |
268 | } | |
269 | ||
270 | return nullptr; | |
187b041e SM |
271 | } |
272 | ||
273 | void | |
480af54c | 274 | displaced_step_buffers::restore_in_ptid (ptid_t ptid) |
187b041e | 275 | { |
480af54c | 276 | for (const displaced_step_buffer &buffer : m_buffers) |
187b041e | 277 | { |
480af54c SM |
278 | if (buffer.current_thread == nullptr) |
279 | continue; | |
280 | ||
281 | regcache *regcache = get_thread_regcache (buffer.current_thread); | |
187b041e SM |
282 | gdbarch *arch = regcache->arch (); |
283 | ULONGEST len = gdbarch_max_insn_length (arch); | |
284 | ||
480af54c | 285 | write_memory_ptid (ptid, buffer.addr, buffer.saved_copy.data (), len); |
187b041e SM |
286 | |
287 | displaced_debug_printf ("restored in ptid %s %s", | |
288 | target_pid_to_str (ptid).c_str (), | |
480af54c | 289 | paddress (arch, buffer.addr)); |
187b041e SM |
290 | } |
291 | } | |
292 | ||
c7acb87b SM |
293 | void _initialize_displaced_stepping (); |
294 | void | |
295 | _initialize_displaced_stepping () | |
296 | { | |
297 | add_setshow_boolean_cmd ("displaced", class_maintenance, | |
298 | &debug_displaced, _("\ | |
299 | Set displaced stepping debugging."), _("\ | |
300 | Show displaced stepping debugging."), _("\ | |
301 | When non-zero, displaced stepping specific debugging is enabled."), | |
302 | NULL, | |
303 | show_debug_displaced, | |
304 | &setdebuglist, &showdebuglist); | |
305 | } |