contrib/plugins/lockstep.c

   1 /*
   2  * Lockstep Execution Plugin
   3  *
   4  * Allows you to execute two QEMU instances in lockstep and report
   5  * when their execution diverges. This is mainly useful for developers
   6  * who want to see where a change to TCG code generation has
   7  * introduced a subtle and hard to find bug.
   8  *
   9  * Caveats:
  10  *   - single-threaded linux-user apps only with non-deterministic syscalls
  11  *   - no MTTCG enabled system emulation (icount may help)
  12  *
  13  * While icount makes things more deterministic it doesn't mean a
  14  * particular run may execute the exact same sequence of blocks. An
  15  * asynchronous event (for example X11 graphics update) may cause a
  16  * block to end early and a new partial block to start. This means
  17  * serial only test cases are a better bet. -d nochain may also help.
  18  *
  19  * This code is not thread safe!
  20  *
  21  * Copyright (c) 2020 Linaro Ltd
  22  *
  23  * SPDX-License-Identifier: GPL-2.0-or-later
  24  */
  25
  26 #include <glib.h>
  27 #include <inttypes.h>
  28 #include <unistd.h>
  29 #include <sys/socket.h>
  30 #include <sys/un.h>
  31 #include <stdio.h>
  32 #include <errno.h>
  33
  34 #include <qemu-plugin.h>
  35
  36 QEMU_PLUGIN_EXPORT int qemu_plugin_version = QEMU_PLUGIN_VERSION;
  37
  38 /* saved so we can uninstall later */
  39 static qemu_plugin_id_t our_id;
  40
  41 static unsigned long bb_count;
  42 static unsigned long insn_count;
  43
  44 /* Information about a translated block */
  45 typedef struct {
  46     uint64_t pc;
  47     uint64_t insns;
  48 } BlockInfo;
  49
  50 /* Information about an execution state in the log */
  51 typedef struct {
  52     BlockInfo *block;
  53     unsigned long insn_count;
  54     unsigned long block_count;
  55 } ExecInfo;
  56
  57 /* The execution state we compare */
  58 typedef struct {
  59     uint64_t pc;
  60     unsigned long insn_count;
  61 } ExecState;
  62
  63 typedef struct {
  64     GSList *log_pos;
  65     int distance;
  66 } DivergeState;
  67
  68 /* list of translated block info */
  69 static GSList *blocks;
  70
  71 /* execution log and points of divergence */
  72 static GSList *log, *divergence_log;
  73
  74 static int socket_fd;
  75 static char *path_to_unlink;
  76
  77 static bool verbose;
  78
  79 static void plugin_cleanup(qemu_plugin_id_t id)
  80 {
  81     /* Free our block data */
  82     g_slist_free_full(blocks, &g_free);
  83     g_slist_free_full(log, &g_free);
  84     g_slist_free(divergence_log);
  85
  86     close(socket_fd);
  87     if (path_to_unlink) {
  88         unlink(path_to_unlink);
  89     }
  90 }
  91
  92 static void plugin_exit(qemu_plugin_id_t id, void *p)
  93 {
  94     g_autoptr(GString) out = g_string_new("No divergence :-)\n");
  95     g_string_append_printf(out, "Executed %ld/%d blocks\n",
  96                            bb_count, g_slist_length(log));
  97     g_string_append_printf(out, "Executed ~%ld instructions\n", insn_count);
  98     qemu_plugin_outs(out->str);
  99
 100     plugin_cleanup(id);
 101 }
 102
 103 static void report_divergance(ExecState *us, ExecState *them)
 104 {
 105     DivergeState divrec = { log, 0 };
 106     g_autoptr(GString) out = g_string_new("");
 107     bool diverged = false;
 108
 109     /*
 110      * If we have diverged before did we get back on track or are we
 111      * totally loosing it?
 112      */
 113     if (divergence_log) {
 114         DivergeState *last = (DivergeState *) divergence_log->data;
 115         GSList *entry;
 116
 117         for (entry = log; g_slist_next(entry); entry = g_slist_next(entry)) {
 118             if (entry == last->log_pos) {
 119                 break;
 120             }
 121             divrec.distance++;
 122         }
 123
 124         /*
 125          * If the last two records are so close it is likely we will
 126          * not recover synchronisation with the other end.
 127          */
 128         if (divrec.distance == 1 && last->distance == 1) {
 129             diverged = true;
 130         }
 131     }
 132     divergence_log = g_slist_prepend(divergence_log,
 133                                      g_memdup(&divrec, sizeof(divrec)));
 134
 135     /* Output short log entry of going out of sync... */
 136     if (verbose || divrec.distance == 1 || diverged) {
 137         g_string_printf(out, "@ %#016lx vs %#016lx (%d/%d since last)\n",
 138                         us->pc, them->pc, g_slist_length(divergence_log),
 139                         divrec.distance);
 140         qemu_plugin_outs(out->str);
 141     }
 142
 143     if (diverged) {
 144         int i;
 145         GSList *entry;
 146
 147         g_string_printf(out, "Δ insn_count @ %#016lx (%ld) vs %#016lx (%ld)\n",
 148                         us->pc, us->insn_count, them->pc, them->insn_count);
 149
 150         for (entry = log, i = 0;
 151              g_slist_next(entry) && i < 5;
 152              entry = g_slist_next(entry), i++) {
 153             ExecInfo *prev = (ExecInfo *) entry->data;
 154             g_string_append_printf(out,
 155                                    "  previously @ %#016lx/%ld (%ld insns)\n",
 156                                    prev->block->pc, prev->block->insns,
 157                                    prev->insn_count);
 158         }
 159         qemu_plugin_outs(out->str);
 160         qemu_plugin_outs("too much divergence... giving up.");
 161         qemu_plugin_uninstall(our_id, plugin_cleanup);
 162     }
 163 }
 164
 165 static void vcpu_tb_exec(unsigned int cpu_index, void *udata)
 166 {
 167     BlockInfo *bi = (BlockInfo *) udata;
 168     ExecState us, them;
 169     ssize_t bytes;
 170     ExecInfo *exec;
 171
 172     us.pc = bi->pc;
 173     us.insn_count = insn_count;
 174
 175     /*
 176      * Write our current position to the other end. If we fail the
 177      * other end has probably died and we should shut down gracefully.
 178      */
 179     bytes = write(socket_fd, &us, sizeof(ExecState));
 180     if (bytes < sizeof(ExecState)) {
 181         qemu_plugin_outs(bytes < 0 ?
 182                          "problem writing to socket" :
 183                          "wrote less than expected to socket");
 184         qemu_plugin_uninstall(our_id, plugin_cleanup);
 185         return;
 186     }
 187
 188     /*
 189      * Now read where our peer has reached. Again a failure probably
 190      * indicates the other end died and we should close down cleanly.
 191      */
 192     bytes = read(socket_fd, &them, sizeof(ExecState));
 193     if (bytes < sizeof(ExecState)) {
 194         qemu_plugin_outs(bytes < 0 ?
 195                          "problem reading from socket" :
 196                          "read less than expected");
 197         qemu_plugin_uninstall(our_id, plugin_cleanup);
 198         return;
 199     }
 200
 201     /*
 202      * Compare and report if we have diverged.
 203      */
 204     if (us.pc != them.pc) {
 205         report_divergance(&us, &them);
 206     }
 207
 208     /*
 209      * Assume this block will execute fully and record it
 210      * in the execution log.
 211      */
 212     insn_count += bi->insns;
 213     bb_count++;
 214     exec = g_new0(ExecInfo, 1);
 215     exec->block = bi;
 216     exec->insn_count = insn_count;
 217     exec->block_count = bb_count;
 218     log = g_slist_prepend(log, exec);
 219 }
 220
 221 static void vcpu_tb_trans(qemu_plugin_id_t id, struct qemu_plugin_tb *tb)
 222 {
 223     BlockInfo *bi = g_new0(BlockInfo, 1);
 224     bi->pc = qemu_plugin_tb_vaddr(tb);
 225     bi->insns = qemu_plugin_tb_n_insns(tb);
 226
 227     /* save a reference so we can free later */
 228     blocks = g_slist_prepend(blocks, bi);
 229     qemu_plugin_register_vcpu_tb_exec_cb(tb, vcpu_tb_exec,
 230                                          QEMU_PLUGIN_CB_NO_REGS, (void *)bi);
 231 }
 232
 233
 234 /*
 235  * Instead of encoding master/slave status into what is essentially
 236  * two peers we shall just take the simple approach of checking for
 237  * the existence of the pipe and assuming if it's not there we are the
 238  * first process.
 239  */
 240 static bool setup_socket(const char *path)
 241 {
 242     struct sockaddr_un sockaddr;
 243     int fd;
 244
 245     fd = socket(AF_UNIX, SOCK_STREAM, 0);
 246     if (fd < 0) {
 247         perror("create socket");
 248         return false;
 249     }
 250
 251     sockaddr.sun_family = AF_UNIX;
 252     g_strlcpy(sockaddr.sun_path, path, sizeof(sockaddr.sun_path) - 1);
 253     if (bind(fd, (struct sockaddr *)&sockaddr, sizeof(sockaddr)) < 0) {
 254         perror("bind socket");
 255         close(fd);
 256         return false;
 257     }
 258
 259     /* remember to clean-up */
 260     path_to_unlink = g_strdup(path);
 261
 262     if (listen(fd, 1) < 0) {
 263         perror("listen socket");
 264         close(fd);
 265         return false;
 266     }
 267
 268     socket_fd = accept(fd, NULL, NULL);
 269     if (socket_fd < 0 && errno != EINTR) {
 270         perror("accept socket");
 271         return false;
 272     }
 273
 274     qemu_plugin_outs("setup_socket::ready\n");
 275
 276     return true;
 277 }
 278
 279 static bool connect_socket(const char *path)
 280 {
 281     int fd;
 282     struct sockaddr_un sockaddr;
 283
 284     fd = socket(AF_UNIX, SOCK_STREAM, 0);
 285     if (fd < 0) {
 286         perror("create socket");
 287         return false;
 288     }
 289
 290     sockaddr.sun_family = AF_UNIX;
 291     g_strlcpy(sockaddr.sun_path, path, sizeof(sockaddr.sun_path) - 1);
 292
 293     if (connect(fd, (struct sockaddr *)&sockaddr, sizeof(sockaddr)) < 0) {
 294         perror("failed to connect");
 295         return false;
 296     }
 297
 298     qemu_plugin_outs("connect_socket::ready\n");
 299
 300     socket_fd = fd;
 301     return true;
 302 }
 303
 304 static bool setup_unix_socket(const char *path)
 305 {
 306     if (g_file_test(path, G_FILE_TEST_EXISTS)) {
 307         return connect_socket(path);
 308     } else {
 309         return setup_socket(path);
 310     }
 311 }
 312
 313
 314 QEMU_PLUGIN_EXPORT int qemu_plugin_install(qemu_plugin_id_t id,
 315                                            const qemu_info_t *info,
 316                                            int argc, char **argv)
 317 {
 318     int i;
 319
 320     if (!argc || !argv[0]) {
 321         qemu_plugin_outs("Need a socket path to talk to other instance.");
 322         return -1;
 323     }
 324
 325     for (i = 0; i < argc; i++) {
 326         char *p = argv[i];
 327         if (strcmp(p, "verbose") == 0) {
 328             verbose = true;
 329         } else if (!setup_unix_socket(argv[0])) {
 330             qemu_plugin_outs("Failed to setup socket for communications.");
 331             return -1;
 332         }
 333     }
 334
 335     our_id = id;
 336
 337     qemu_plugin_register_vcpu_tb_trans_cb(id, vcpu_tb_trans);
 338     qemu_plugin_register_atexit_cb(id, plugin_exit, NULL);
 339     return 0;
 340 }