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   guint64 symfile_size;
  82 };
  83
  84 struct jit_descriptor
  85 {
  86   guint32 version;
  87   /* This type should be jit_actions_t, but we use guint32
  88      to be explicit about the bitwidth.  */
  89   guint32 action_flag;
  90   struct jit_code_entry *relevant_entry;
  91   struct jit_code_entry *first_entry;
  92 };
  93
  94
  95 #ifdef _MSC_VER
  96 #define MONO_NOINLINE __declspec (noinline)
  97 #else
  98 #define MONO_NOINLINE __attribute__((noinline))
  99 #endif
 100
 101 /* GDB puts a breakpoint in this function.  */
 102 void MONO_NOINLINE __jit_debug_register_code(void);
 103
 104 #if defined(ENABLE_LLVM) && ((LLVM_MAJOR_VERSION == 2 && LLVM_MINOR_VERSION >= 7) || LLVM_MAJOR_VERSION > 2)
 105 /* LLVM already defines these */
 106 extern struct jit_descriptor __jit_debug_descriptor;
 107 #else
 108
 109 /* Make sure to specify the version statically, because the
 110    debugger may check the version before we can set it.  */
 111 struct jit_descriptor __jit_debug_descriptor = { 1, 0, 0, 0 };
 112
 113 void MONO_NOINLINE __jit_debug_register_code(void) { };
 114 #endif
 115
 116 static MonoImageWriter *xdebug_w;
 117 static MonoDwarfWriter *xdebug_writer;
 118 static FILE *xdebug_fp, *il_file;
 119 static gboolean use_gdb_interface, save_symfiles;
 120 static int il_file_line_index;
 121 static GHashTable *xdebug_syms;
 122
 123 void
 124 mono_xdebug_init (char *options)
 125 {
 126         MonoImageWriter *w;
 127         char **args, **ptr;
 128
 129         args = g_strsplit (options, ",", -1);
 130         for (ptr = args; ptr && *ptr; ptr ++) {
 131                 char *arg = *ptr;
 132
 133                 if (!strcmp (arg, "gdb"))
 134                         use_gdb_interface = TRUE;
 135                 if (!strcmp (arg, "save-symfiles"))
 136                         save_symfiles = TRUE;
 137         }
 138
 139         /* This file will contain the IL code for methods which don't have debug info */
 140         il_file = fopen ("xdb.il", "w");
 141
 142         if (use_gdb_interface)
 143                 return;
 144
 145         unlink ("xdb.s");
 146         xdebug_fp = fopen ("xdb.s", "w");
 147
 148         w = img_writer_create (xdebug_fp, FALSE);
 149
 150         img_writer_emit_start (w);
 151
 152         xdebug_writer = mono_dwarf_writer_create (w, il_file, 0, TRUE);
 153
 154         /* Emit something so the file has a text segment */
 155         img_writer_emit_section_change (w, ".text", 0);
 156         img_writer_emit_string (w, "");
 157
 158         mono_dwarf_writer_emit_base_info (xdebug_writer, mono_unwind_get_cie_program ());
 159 }
 160
 161 static void
 162 xdebug_begin_emit (MonoImageWriter **out_w, MonoDwarfWriter **out_dw)
 163 {
 164         MonoImageWriter *w;
 165         MonoDwarfWriter *dw;
 166
 167         w = img_writer_create (NULL, TRUE);
 168
 169         img_writer_emit_start (w);
 170
 171         /* This file will contain the IL code for methods which don't have debug info */
 172         if (!il_file)
 173                 il_file = fopen ("xdb.il", "w");
 174
 175         dw = mono_dwarf_writer_create (w, il_file, il_file_line_index, FALSE);
 176
 177         mono_dwarf_writer_emit_base_info (dw, mono_unwind_get_cie_program ());
 178
 179         *out_w = w;
 180         *out_dw = dw;
 181 }
 182
 183 static void
 184 xdebug_end_emit (MonoImageWriter *w, MonoDwarfWriter *dw, MonoMethod *method)
 185 {
 186         guint8 *img;
 187         guint32 img_size;
 188         struct jit_code_entry *entry;
 189
 190         il_file_line_index = mono_dwarf_writer_get_il_file_line_index (dw);
 191         mono_dwarf_writer_close (dw);
 192
 193         img_writer_emit_writeout (w);
 194
 195         img = img_writer_get_output (w, &img_size);
 196
 197         img_writer_destroy (w);
 198
 199         if (FALSE) {
 200                 /* Save the symbol files to help debugging */
 201                 FILE *fp;
 202                 char *file_name;
 203                 static int file_counter;
 204
 205                 file_counter ++;
 206                 file_name = g_strdup_printf ("xdb-%d.o", file_counter);
 207                 //printf ("%s -> %s\n", mono_method_full_name (method, TRUE), file_name);
 208
 209                 fp = fopen (file_name, "w");
 210                 fwrite (img, img_size, 1, fp);
 211                 fclose (fp);
 212                 g_free (file_name);
 213         }
 214
 215         /* Register the image with GDB */
 216
 217         entry = g_malloc (sizeof (struct jit_code_entry));
 218
 219         entry->symfile_addr = (const char*)img;
 220         entry->symfile_size = img_size;
 221
 222         entry->next_entry = __jit_debug_descriptor.first_entry;
 223         if (__jit_debug_descriptor.first_entry)
 224                 __jit_debug_descriptor.first_entry->prev_entry = entry;
 225         __jit_debug_descriptor.first_entry = entry;
 226
 227         __jit_debug_descriptor.relevant_entry = entry;
 228         __jit_debug_descriptor.action_flag = JIT_REGISTER_FN;
 229
 230         __jit_debug_register_code ();
 231 }
 232
 233 /*
 234  * mono_xdebug_flush:
 235  *
 236  *   This could be called from inside gdb to flush the debugging information not yet
 237  * registered with gdb.
 238  */
 239 void
 240 mono_xdebug_flush (void)
 241 {
 242         if (xdebug_w)
 243                 xdebug_end_emit (xdebug_w, xdebug_writer, NULL);
 244
 245         xdebug_begin_emit (&xdebug_w, &xdebug_writer);
 246 }
 247
 248 static int xdebug_method_count;
 249
 250 /*
 251  * mono_save_xdebug_info:
 252  *
 253  *   Emit debugging info for METHOD into an assembly file which can be assembled
 254  * and loaded into gdb to provide debugging info for JITted code.
 255  * LOCKING: Acquires the loader lock.
 256  */
 257 void
 258 mono_save_xdebug_info (MonoCompile *cfg)
 259 {
 260         if (use_gdb_interface) {
 261                 mono_loader_lock ();
 262
 263                 if (!xdebug_syms)
 264                         xdebug_syms = g_hash_table_new_full (g_str_hash, g_str_equal, g_free, NULL);
 265
 266                 /*
 267                  * gdb is not designed to handle 1000s of symbol files (one per method). So we
 268                  * group them into groups of 100.
 269                  */
 270                 if ((xdebug_method_count % 100) == 0)
 271                         mono_xdebug_flush ();
 272
 273                 xdebug_method_count ++;
 274
 275                 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, mono_debug_find_method (cfg->jit_info->method, mono_domain_get ()));
 276
 277 #if 0
 278                 /*
 279                  * Emit a symbol for the code by emitting it at the beginning of the text
 280                  * segment, and setting the text segment to have an absolute address.
 281                  * This symbol can be used to set breakpoints in gdb.
 282                  * FIXME: This doesn't work when multiple methods are emitted into the same file.
 283                  */
 284                 sym = get_debug_sym (cfg->jit_info->method, "", xdebug_syms);
 285                 img_writer_emit_section_change (w, ".text", 0);
 286                 if (!xdebug_text_addr) {
 287                         xdebug_text_addr = cfg->jit_info->code_start;
 288                         img_writer_set_section_addr (w, (gssize)xdebug_text_addr);
 289                 }
 290                 img_writer_emit_global_with_size (w, sym, cfg->jit_info->code_size, TRUE);
 291                 img_writer_emit_label (w, sym);
 292                 img_writer_emit_bytes (w, cfg->jit_info->code_start, cfg->jit_info->code_size);
 293                 g_free (sym);
 294 #endif
 295
 296                 mono_loader_unlock ();
 297         } else {
 298                 if (!xdebug_writer)
 299                         return;
 300
 301                 mono_loader_lock ();
 302                 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, mono_debug_find_method (cfg->jit_info->method, mono_domain_get ()));
 303                 fflush (xdebug_fp);
 304                 mono_loader_unlock ();
 305         }
 306 }
 307
 308 /*
 309  * mono_save_trampoline_xdebug_info:
 310  *
 311  *   Same as mono_save_xdebug_info, but for trampolines.
 312  * LOCKING: Acquires the loader lock.
 313  */
 314 void
 315 mono_save_trampoline_xdebug_info (const char *tramp_name, guint8 *code, guint32 code_size, GSList *unwind_info)
 316 {
 317         if (use_gdb_interface) {
 318                 MonoImageWriter *w;
 319                 MonoDwarfWriter *dw;
 320
 321                 mono_loader_lock ();
 322
 323                 xdebug_begin_emit (&w, &dw);
 324
 325                 mono_dwarf_writer_emit_trampoline (dw, tramp_name, NULL, NULL, code, code_size, unwind_info);
 326
 327                 xdebug_end_emit (w, dw, NULL);
 328
 329                 mono_loader_unlock ();
 330         } else {
 331                 if (!xdebug_writer)
 332                         return;
 333
 334                 mono_loader_lock ();
 335                 mono_dwarf_writer_emit_trampoline (xdebug_writer, tramp_name, NULL, NULL, code, code_size, unwind_info);
 336                 fflush (xdebug_fp);
 337                 mono_loader_unlock ();
 338         }
 339 }
 340
 341 #else /* !defined(DISABLE_AOT) && !defined(DISABLE_JIT) */
 342
 343 void
 344 mono_xdebug_init (char *options)
 345 {
 346 }
 347
 348 void
 349 mono_save_xdebug_info (MonoCompile *cfg)
 350 {
 351 }
 352
 353 void
 354 mono_save_trampoline_xdebug_info (const char *tramp_name, guint8 *code, guint32 code_size, GSList *unwind_info)
 355 {
 356 }
 357
 358 #endif