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)
  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 #define USE_GDB_JIT_INTERFACE
  55
  56 /* The recommended gdb macro is: */
  57 /*
  58   define xdb
  59   shell rm -f xdb.so && as --64 -o xdb.o xdb.s && ld -shared -o xdb.so xdb.o
  60   add-symbol-file xdb.so 0
  61   end
  62 */
  63
  64 /*
  65  * GDB JIT interface definitions.
  66  *
  67  *      http://sources.redhat.com/gdb/onlinedocs/gdb_30.html
  68  */
  69 typedef enum
  70 {
  71   JIT_NOACTION = 0,
  72   JIT_REGISTER_FN,
  73   JIT_UNREGISTER_FN
  74 } jit_actions_t;
  75
  76 struct jit_code_entry
  77 {
  78         struct jit_code_entry *next_entry;
  79         struct jit_code_entry *prev_entry;
  80         const char *symfile_addr;
  81         /*
  82          * The gdb code in gdb/jit.c which reads this structure ignores alignment
  83          * requirements, so use two 32 bit fields.
  84          */
  85         guint32 symfile_size1, symfile_size2;
  86 };
  87
  88 struct jit_descriptor
  89 {
  90   guint32 version;
  91   /* This type should be jit_actions_t, but we use guint32
  92      to be explicit about the bitwidth.  */
  93   guint32 action_flag;
  94   struct jit_code_entry *relevant_entry;
  95   struct jit_code_entry *first_entry;
  96 };
  97
  98
  99 #ifdef _MSC_VER
 100 #define MONO_NOINLINE __declspec (noinline)
 101 #else
 102 #define MONO_NOINLINE __attribute__((noinline))
 103 #endif
 104
 105 /* GDB puts a breakpoint in this function.  */
 106 void MONO_NOINLINE __jit_debug_register_code(void);
 107
 108 /* Make sure to specify the version statically, because the
 109    debugger may check the version before we can set it.  */
 110 struct jit_descriptor __jit_debug_descriptor = { 1, 0, 0, 0 };
 111
 112 /* gcc seems to inline/eliminate calls to noinline functions, thus the asm () */
 113 void MONO_NOINLINE __jit_debug_register_code(void) {
 114 #if defined(__GNUC__)
 115         asm ("");
 116 #endif
 117 }
 118
 119 static MonoImageWriter *xdebug_w;
 120 static MonoDwarfWriter *xdebug_writer;
 121 static FILE *xdebug_fp, *il_file;
 122 static gboolean use_gdb_interface, save_symfiles;
 123 static int il_file_line_index;
 124 static GHashTable *xdebug_syms;
 125
 126 void
 127 mono_xdebug_init (char *options)
 128 {
 129         MonoImageWriter *w;
 130         char **args, **ptr;
 131
 132         args = g_strsplit (options, ",", -1);
 133         for (ptr = args; ptr && *ptr; ptr ++) {
 134                 char *arg = *ptr;
 135
 136                 if (!strcmp (arg, "gdb"))
 137                         use_gdb_interface = TRUE;
 138                 if (!strcmp (arg, "save-symfiles"))
 139                         save_symfiles = TRUE;
 140         }
 141
 142         /* This file will contain the IL code for methods which don't have debug info */
 143         il_file = fopen ("xdb.il", "w");
 144         if (il_file == NULL) {
 145                 use_gdb_interface = FALSE;
 146                 g_warning ("** Unable to create xdb.il. Managed symbol names won't be available.");
 147                 return;
 148         }
 149
 150         if (use_gdb_interface)
 151                 return;
 152
 153         unlink ("xdb.s");
 154         xdebug_fp = fopen ("xdb.s", "w");
 155
 156         w = img_writer_create (xdebug_fp, FALSE);
 157
 158         img_writer_emit_start (w);
 159
 160         xdebug_writer = mono_dwarf_writer_create (w, il_file, 0, TRUE);
 161
 162         /* Emit something so the file has a text segment */
 163         img_writer_emit_section_change (w, ".text", 0);
 164         img_writer_emit_string (w, "");
 165
 166         mono_dwarf_writer_emit_base_info (xdebug_writer, mono_unwind_get_cie_program ());
 167 }
 168
 169 static void
 170 xdebug_begin_emit (MonoImageWriter **out_w, MonoDwarfWriter **out_dw)
 171 {
 172         MonoImageWriter *w;
 173         MonoDwarfWriter *dw;
 174
 175         w = img_writer_create (NULL, TRUE);
 176
 177         img_writer_emit_start (w);
 178
 179         /* This file will contain the IL code for methods which don't have debug info */
 180         if (!il_file)
 181                 il_file = fopen ("xdb.il", "w");
 182
 183         dw = mono_dwarf_writer_create (w, il_file, il_file_line_index, FALSE);
 184
 185         mono_dwarf_writer_emit_base_info (dw, mono_unwind_get_cie_program ());
 186
 187         *out_w = w;
 188         *out_dw = dw;
 189 }
 190
 191 static void
 192 xdebug_end_emit (MonoImageWriter *w, MonoDwarfWriter *dw, MonoMethod *method)
 193 {
 194         guint8 *img;
 195         guint32 img_size;
 196         struct jit_code_entry *entry;
 197         guint64 *psize;
 198
 199         il_file_line_index = mono_dwarf_writer_get_il_file_line_index (dw);
 200         mono_dwarf_writer_close (dw);
 201
 202         img_writer_emit_writeout (w);
 203
 204         img = img_writer_get_output (w, &img_size);
 205
 206         img_writer_destroy (w);
 207
 208         if (FALSE) {
 209                 /* Save the symbol files to help debugging */
 210                 FILE *fp;
 211                 char *file_name;
 212                 static int file_counter;
 213
 214                 file_counter ++;
 215                 file_name = g_strdup_printf ("xdb-%d.o", file_counter);
 216                 printf ("%s %p %d\n", file_name, img, img_size);
 217
 218                 fp = fopen (file_name, "w");
 219                 fwrite (img, img_size, 1, fp);
 220                 fclose (fp);
 221                 g_free (file_name);
 222         }
 223
 224         /* Register the image with GDB */
 225
 226         entry = g_malloc0 (sizeof (struct jit_code_entry));
 227
 228         entry->symfile_addr = (const char*)img;
 229         psize = (guint64*)&entry->symfile_size1;
 230         *psize = img_size;
 231
 232         entry->next_entry = __jit_debug_descriptor.first_entry;
 233         if (__jit_debug_descriptor.first_entry)
 234                 __jit_debug_descriptor.first_entry->prev_entry = entry;
 235         __jit_debug_descriptor.first_entry = entry;
 236
 237         __jit_debug_descriptor.relevant_entry = entry;
 238         __jit_debug_descriptor.action_flag = JIT_REGISTER_FN;
 239
 240         __jit_debug_register_code ();
 241 }
 242
 243 /*
 244  * mono_xdebug_flush:
 245  *
 246  *   This could be called from inside gdb to flush the debugging information not yet
 247  * registered with gdb.
 248  */
 249 void
 250 mono_xdebug_flush (void)
 251 {
 252         if (xdebug_w)
 253                 xdebug_end_emit (xdebug_w, xdebug_writer, NULL);
 254
 255         xdebug_begin_emit (&xdebug_w, &xdebug_writer);
 256 }
 257
 258 static int xdebug_method_count;
 259
 260 /*
 261  * mono_save_xdebug_info:
 262  *
 263  *   Emit debugging info for METHOD into an assembly file which can be assembled
 264  * and loaded into gdb to provide debugging info for JITted code.
 265  * LOCKING: Acquires the loader lock.
 266  */
 267 void
 268 mono_save_xdebug_info (MonoCompile *cfg)
 269 {
 270         MonoDebugMethodJitInfo *dmji;
 271
 272         if (use_gdb_interface) {
 273                 mono_loader_lock ();
 274
 275                 if (!xdebug_syms)
 276                         xdebug_syms = g_hash_table_new_full (g_str_hash, g_str_equal, g_free, NULL);
 277
 278                 /*
 279                  * gdb is not designed to handle 1000s of symbol files (one per method). So we
 280                  * group them into groups of 100.
 281                  */
 282                 if ((xdebug_method_count % 100) == 0)
 283                         mono_xdebug_flush ();
 284
 285                 xdebug_method_count ++;
 286
 287                 dmji = mono_debug_find_method (cfg->jit_info->method, mono_domain_get ());;
 288                 mono_dwarf_writer_emit_method (xdebug_writer, cfg, cfg->jit_info->method, NULL, NULL, cfg->jit_info->code_start, cfg->jit_info->code_size, cfg->args, cfg->locals, cfg->unwind_ops, dmji);
 289                 mono_debug_free_method_jit_info (dmji);
 290
 291 #if 0
 292                 /*
 293                  * Emit a symbol for the code by emitting it at the beginning of the text
 294                  * segment, and setting the text segment to have an absolute address.
 295                  * This symbol can be used to set breakpoints in gdb.
 296                  * FIXME: This doesn't work when multiple methods are emitted into the same file.
 297                  */
 298                 sym = get_debug_sym (cfg->jit_info->method, "", xdebug_syms);
 299                 img_writer_emit_section_change (w, ".text", 0);
 300                 if (!xdebug_text_addr) {
 301                         xdebug_text_addr = cfg->jit_info->code_start;
 302                         img_writer_set_section_addr (w, (gssize)xdebug_text_addr);
 303                 }
 304                 img_writer_emit_global_with_size (w, sym, cfg->jit_info->code_size, TRUE);
 305                 img_writer_emit_label (w, sym);
 306                 img_writer_emit_bytes (w, cfg->jit_info->code_start, cfg->jit_info->code_size);
 307                 g_free (sym);
 308 #endif
 309
 310                 mono_loader_unlock ();
 311         } else {
 312                 if (!xdebug_writer)
 313                         return;
 314
 315                 mono_loader_lock ();
 316                 dmji = mono_debug_find_method (cfg->jit_info->method, mono_domain_get ());;
 317                 mono_dwarf_writer_emit_method (xdebug_writer, cfg, cfg->jit_info->method, NULL, NULL, cfg->jit_info->code_start, cfg->jit_info->code_size, cfg->args, cfg->locals, cfg->unwind_ops, dmji);
 318                 mono_debug_free_method_jit_info (dmji);
 319                 fflush (xdebug_fp);
 320                 mono_loader_unlock ();
 321         }
 322
 323 }
 324
 325 /*
 326  * mono_save_trampoline_xdebug_info:
 327  *
 328  *   Same as mono_save_xdebug_info, but for trampolines.
 329  * LOCKING: Acquires the loader lock.
 330  */
 331 void
 332 mono_save_trampoline_xdebug_info (MonoTrampInfo *info)
 333 {
 334         if (use_gdb_interface) {
 335                 MonoImageWriter *w;
 336                 MonoDwarfWriter *dw;
 337
 338                 /* This can be called before the loader lock is initialized */
 339                 mono_loader_lock_if_inited ();
 340
 341                 xdebug_begin_emit (&w, &dw);
 342
 343                 mono_dwarf_writer_emit_trampoline (dw, info->name, NULL, NULL, info->code, info->code_size, info->unwind_ops);
 344
 345                 xdebug_end_emit (w, dw, NULL);
 346
 347                 mono_loader_unlock_if_inited ();
 348         } else {
 349                 if (!xdebug_writer)
 350                         return;
 351
 352                 mono_loader_lock_if_inited ();
 353                 mono_dwarf_writer_emit_trampoline (xdebug_writer, info->name, NULL, NULL, info->code, info->code_size, info->unwind_ops);
 354                 fflush (xdebug_fp);
 355                 mono_loader_unlock_if_inited ();
 356         }
 357 }
 358
 359 #else /* !defined(DISABLE_AOT) && !defined(DISABLE_JIT) */
 360
 361 void
 362 mono_xdebug_init (char *options)
 363 {
 364 }
 365
 366 void
 367 mono_save_xdebug_info (MonoCompile *cfg)
 368 {
 369 }
 370
 371 void
 372 mono_save_trampoline_xdebug_info (MonoTrampInfo *info)
 373 {
 374 }
 375
 376 #endif