mono/mini/xdebug.c

   1 /*
   2  * xdebug.c: Support for emitting gdb debug info for JITted code.
   3  *
   4  * Author:
   5  *   Zoltan Varga (vargaz@gmail.com)
   6  *
   7  * (C) 2010 Novell, Inc.
   8  */
   9
  10 /*
  11  * This works as follows:
  12  * - the runtime writes out an xdb.s file containing DWARF debug info.
  13  * - the user calls a gdb macro
  14  * - the macro compiles and loads this shared library using add-symbol-file.
  15  *
  16  * This is based on the xdebug functionality in the Kaffe Java VM.
  17  *
  18  * We emit assembly code instead of using the ELF writer, so we can emit debug info
  19  * incrementally as each method is JITted, and the debugger doesn't have to call
  20  * into the runtime to emit the shared library, which would cause all kinds of
  21  * complications, like threading issues, and the fact that the ELF writer's
  22  * emit_writeout () function cannot be called more than once.
  23  * GDB 7.0 and later has a JIT interface.
  24  */
  25
  26 #include "config.h"
  27 #include <glib.h>
  28 #include "mini.h"
  29
  30 #if !defined(DISABLE_AOT) && !defined(DISABLE_JIT) && USE_BIN_WRITER
  31 #include <sys/types.h>
  32 #ifdef HAVE_UNISTD_H
  33 #include <unistd.h>
  34 #endif
  35 #ifdef HAVE_STDINT_H
  36 #include <stdint.h>
  37 #endif
  38 #include <fcntl.h>
  39 #include <ctype.h>
  40 #include <string.h>
  41 #ifndef HOST_WIN32
  42 #include <sys/time.h>
  43 #else
  44 #include <winsock2.h>
  45 #include <windows.h>
  46 #endif
  47
  48 #include <errno.h>
  49 #include <sys/stat.h>
  50
  51 #include "image-writer.h"
  52 #include "dwarfwriter.h"
  53
  54 #include "mono/utils/mono-compiler.h"
  55
  56 #define USE_GDB_JIT_INTERFACE
  57
  58 /* The recommended gdb macro is: */
  59 /*
  60   define xdb
  61   shell rm -f xdb.so && as --64 -o xdb.o xdb.s && ld -shared -o xdb.so xdb.o
  62   add-symbol-file xdb.so 0
  63   end
  64 */
  65
  66 /*
  67  * GDB JIT interface definitions.
  68  *
  69  *      http://sources.redhat.com/gdb/onlinedocs/gdb_30.html
  70  */
  71 typedef enum
  72 {
  73   JIT_NOACTION = 0,
  74   JIT_REGISTER_FN,
  75   JIT_UNREGISTER_FN
  76 } jit_actions_t;
  77
  78 struct jit_code_entry
  79 {
  80         struct jit_code_entry *next_entry;
  81         struct jit_code_entry *prev_entry;
  82         const char *symfile_addr;
  83         /*
  84          * The gdb code in gdb/jit.c which reads this structure ignores alignment
  85          * requirements, so use two 32 bit fields.
  86          */
  87         guint32 symfile_size1, symfile_size2;
  88 };
  89
  90 struct jit_descriptor
  91 {
  92   guint32 version;
  93   /* This type should be jit_actions_t, but we use guint32
  94      to be explicit about the bitwidth.  */
  95   guint32 action_flag;
  96   struct jit_code_entry *relevant_entry;
  97   struct jit_code_entry *first_entry;
  98 };
  99
 100 /* GDB puts a breakpoint in this function.  */
 101 void MONO_NEVER_INLINE __jit_debug_register_code(void);
 102
 103 #if !defined(MONO_LLVM_LOADED) && defined(ENABLE_LLVM) && !defined(MONO_CROSS_COMPILE)
 104
 105 /* LLVM already defines these */
 106
 107 extern struct jit_descriptor __jit_debug_descriptor;
 108
 109 #else
 110
 111 /* gcc seems to inline/eliminate calls to noinline functions, thus the asm () */
 112 void MONO_NEVER_INLINE __jit_debug_register_code(void) {
 113 #if defined(__GNUC__)
 114         asm ("");
 115 #endif
 116 }
 117
 118 /* Make sure to specify the version statically, because the
 119    debugger may check the version before we can set it.  */
 120 struct jit_descriptor __jit_debug_descriptor = { 1, 0, 0, 0 };
 121
 122 #endif
 123
 124 static MonoImageWriter *xdebug_w;
 125 static MonoDwarfWriter *xdebug_writer;
 126 static FILE *xdebug_fp, *il_file;
 127 static gboolean use_gdb_interface, save_symfiles;
 128 static int il_file_line_index;
 129 static GHashTable *xdebug_syms;
 130
 131 void
 132 mono_xdebug_init (const char *options)
 133 {
 134         MonoImageWriter *w;
 135         char **args, **ptr;
 136
 137         args = g_strsplit (options, ",", -1);
 138         for (ptr = args; ptr && *ptr; ptr ++) {
 139                 char *arg = *ptr;
 140
 141                 if (!strcmp (arg, "gdb"))
 142                         use_gdb_interface = TRUE;
 143                 if (!strcmp (arg, "save-symfiles"))
 144                         save_symfiles = TRUE;
 145         }
 146
 147         /* This file will contain the IL code for methods which don't have debug info */
 148         il_file = fopen ("xdb.il", "w");
 149         if (il_file == NULL) {
 150                 use_gdb_interface = FALSE;
 151                 g_warning ("** Unable to create xdb.il. Managed symbol names won't be available.");
 152                 return;
 153         }
 154
 155         if (use_gdb_interface)
 156                 return;
 157
 158         unlink ("xdb.s");
 159         xdebug_fp = fopen ("xdb.s", "w");
 160
 161         w = mono_img_writer_create (xdebug_fp, FALSE);
 162
 163         mono_img_writer_emit_start (w);
 164
 165         xdebug_writer = mono_dwarf_writer_create (w, il_file, 0, TRUE);
 166
 167         /* Emit something so the file has a text segment */
 168         mono_img_writer_emit_section_change (w, ".text", 0);
 169         mono_img_writer_emit_string (w, "");
 170
 171         mono_dwarf_writer_emit_base_info (xdebug_writer, "JITted code", mono_unwind_get_cie_program ());
 172 }
 173
 174 static void
 175 xdebug_begin_emit (MonoImageWriter **out_w, MonoDwarfWriter **out_dw)
 176 {
 177         MonoImageWriter *w;
 178         MonoDwarfWriter *dw;
 179
 180         w = mono_img_writer_create (NULL, TRUE);
 181
 182         mono_img_writer_emit_start (w);
 183
 184         /* This file will contain the IL code for methods which don't have debug info */
 185         if (!il_file)
 186                 il_file = fopen ("xdb.il", "w");
 187
 188         dw = mono_dwarf_writer_create (w, il_file, il_file_line_index, TRUE);
 189
 190         mono_dwarf_writer_emit_base_info (dw, "JITted code", mono_unwind_get_cie_program ());
 191
 192         *out_w = w;
 193         *out_dw = dw;
 194 }
 195
 196 static void
 197 xdebug_end_emit (MonoImageWriter *w, MonoDwarfWriter *dw, MonoMethod *method)
 198 {
 199         guint8 *img;
 200         guint32 img_size;
 201         struct jit_code_entry *entry;
 202         guint64 *psize;
 203
 204         il_file_line_index = mono_dwarf_writer_get_il_file_line_index (dw);
 205         mono_dwarf_writer_close (dw);
 206
 207         mono_img_writer_emit_writeout (w);
 208
 209         img = mono_img_writer_get_output (w, &img_size);
 210
 211         mono_img_writer_destroy (w);
 212
 213         if (FALSE) {
 214                 /* Save the symbol files to help debugging */
 215                 FILE *fp;
 216                 char *file_name;
 217                 static int file_counter;
 218
 219                 file_counter ++;
 220                 file_name = g_strdup_printf ("xdb-%d.o", file_counter);
 221                 printf ("%s %p %d\n", file_name, img, img_size);
 222
 223                 fp = fopen (file_name, "w");
 224                 fwrite (img, img_size, 1, fp);
 225                 fclose (fp);
 226                 g_free (file_name);
 227         }
 228
 229         /* Register the image with GDB */
 230
 231         entry = g_malloc0 (sizeof (struct jit_code_entry));
 232
 233         entry->symfile_addr = (const char*)img;
 234         psize = (guint64*)&entry->symfile_size1;
 235         *psize = img_size;
 236
 237         entry->next_entry = __jit_debug_descriptor.first_entry;
 238         if (__jit_debug_descriptor.first_entry)
 239                 __jit_debug_descriptor.first_entry->prev_entry = entry;
 240         __jit_debug_descriptor.first_entry = entry;
 241
 242         __jit_debug_descriptor.relevant_entry = entry;
 243         __jit_debug_descriptor.action_flag = JIT_REGISTER_FN;
 244
 245         __jit_debug_register_code ();
 246 }
 247
 248 /*
 249  * mono_xdebug_flush:
 250  *
 251  *   This could be called from inside gdb to flush the debugging information not yet
 252  * registered with gdb.
 253  */
 254 void
 255 mono_xdebug_flush (void)
 256 {
 257         if (xdebug_w)
 258                 xdebug_end_emit (xdebug_w, xdebug_writer, NULL);
 259
 260         xdebug_begin_emit (&xdebug_w, &xdebug_writer);
 261 }
 262
 263 static int xdebug_method_count;
 264
 265 /*
 266  * mono_save_xdebug_info:
 267  *
 268  *   Emit debugging info for METHOD into an assembly file which can be assembled
 269  * and loaded into gdb to provide debugging info for JITted code.
 270  * LOCKING: Acquires the loader lock.
 271  */
 272 void
 273 mono_save_xdebug_info (MonoCompile *cfg)
 274 {
 275         MonoDebugMethodJitInfo *dmji;
 276
 277         if (use_gdb_interface) {
 278                 mono_loader_lock ();
 279
 280                 if (!xdebug_syms)
 281                         xdebug_syms = g_hash_table_new_full (g_str_hash, g_str_equal, g_free, NULL);
 282
 283                 /*
 284                  * gdb is not designed to handle 1000s of symbol files (one per method). So we
 285                  * group them into groups of 100.
 286                  */
 287                 if ((xdebug_method_count % 100) == 0)
 288                         mono_xdebug_flush ();
 289
 290                 xdebug_method_count ++;
 291
 292                 dmji = mono_debug_find_method (jinfo_get_method (cfg->jit_info), mono_domain_get ());;
 293                 mono_dwarf_writer_emit_method (xdebug_writer, cfg, jinfo_get_method (cfg->jit_info), NULL, NULL, NULL,
 294                                                                            cfg->jit_info->code_start, cfg->jit_info->code_size, cfg->args, cfg->locals, cfg->unwind_ops, dmji);
 295                 mono_debug_free_method_jit_info (dmji);
 296
 297 #if 0
 298                 /*
 299                  * Emit a symbol for the code by emitting it at the beginning of the text
 300                  * segment, and setting the text segment to have an absolute address.
 301                  * This symbol can be used to set breakpoints in gdb.
 302                  * FIXME: This doesn't work when multiple methods are emitted into the same file.
 303                  */
 304                 sym = get_debug_sym (cfg->jit_info->method, "", xdebug_syms);
 305                 mono_img_writer_emit_section_change (w, ".text", 0);
 306                 if (!xdebug_text_addr) {
 307                         xdebug_text_addr = cfg->jit_info->code_start;
 308                         mono_img_writer_set_section_addr (w, (gssize)xdebug_text_addr);
 309                 }
 310                 mono_img_writer_emit_global_with_size (w, sym, cfg->jit_info->code_size, TRUE);
 311                 mono_img_writer_emit_label (w, sym);
 312                 mono_img_writer_emit_bytes (w, cfg->jit_info->code_start, cfg->jit_info->code_size);
 313                 g_free (sym);
 314 #endif
 315
 316                 mono_loader_unlock ();
 317         } else {
 318                 if (!xdebug_writer)
 319                         return;
 320
 321                 mono_loader_lock ();
 322                 dmji = mono_debug_find_method (jinfo_get_method (cfg->jit_info), mono_domain_get ());
 323                 mono_dwarf_writer_emit_method (xdebug_writer, cfg, jinfo_get_method (cfg->jit_info), NULL, NULL, NULL,
 324                                                                            cfg->jit_info->code_start, cfg->jit_info->code_size, cfg->args, cfg->locals, cfg->unwind_ops, dmji);
 325                 mono_debug_free_method_jit_info (dmji);
 326                 fflush (xdebug_fp);
 327                 mono_loader_unlock ();
 328         }
 329
 330 }
 331
 332 /*
 333  * mono_save_trampoline_xdebug_info:
 334  *
 335  *   Same as mono_save_xdebug_info, but for trampolines.
 336  * LOCKING: Acquires the loader lock.
 337  */
 338 void
 339 mono_save_trampoline_xdebug_info (MonoTrampInfo *info)
 340 {
 341         if (use_gdb_interface) {
 342                 MonoImageWriter *w;
 343                 MonoDwarfWriter *dw;
 344
 345                 /* This can be called before the loader lock is initialized */
 346                 mono_loader_lock_if_inited ();
 347
 348                 xdebug_begin_emit (&w, &dw);
 349
 350                 mono_dwarf_writer_emit_trampoline (dw, info->name, NULL, NULL, info->code, info->code_size, info->unwind_ops);
 351
 352                 xdebug_end_emit (w, dw, NULL);
 353
 354                 mono_loader_unlock_if_inited ();
 355         } else {
 356                 if (!xdebug_writer)
 357                         return;
 358
 359                 mono_loader_lock_if_inited ();
 360                 mono_dwarf_writer_emit_trampoline (xdebug_writer, info->name, NULL, NULL, info->code, info->code_size, info->unwind_ops);
 361                 fflush (xdebug_fp);
 362                 mono_loader_unlock_if_inited ();
 363         }
 364 }
 365
 366 #else /* !defined(DISABLE_AOT) && !defined(DISABLE_JIT) */
 367
 368 void
 369 mono_xdebug_init (const char *options)
 370 {
 371 }
 372
 373 void
 374 mono_save_xdebug_info (MonoCompile *cfg)
 375 {
 376 }
 377
 378 void
 379 mono_save_trampoline_xdebug_info (MonoTrampInfo *info)
 380 {
 381 }
 382
 383 #endif