2 * xdebug.c: Support for emitting gdb debug info for JITted code.
5 * Zoltan Varga (vargaz@gmail.com)
7 * (C) 2010 Novell, Inc.
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.
16 * This is based on the xdebug functionality in the Kaffe Java VM.
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.
30 #if !defined(DISABLE_AOT) && !defined(DISABLE_JIT) && USE_BIN_WRITER
31 #include <sys/types.h>
51 #include "image-writer.h"
52 #include "dwarfwriter.h"
54 #include "mono/utils/mono-compiler.h"
56 #define USE_GDB_JIT_INTERFACE
58 /* The recommended gdb macro is: */
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
67 * GDB JIT interface definitions.
69 * http://sources.redhat.com/gdb/onlinedocs/gdb_30.html
80 struct jit_code_entry *next_entry;
81 struct jit_code_entry *prev_entry;
82 const char *symfile_addr;
84 * The gdb code in gdb/jit.c which reads this structure ignores alignment
85 * requirements, so use two 32 bit fields.
87 guint32 symfile_size1, symfile_size2;
93 /* This type should be jit_actions_t, but we use guint32
94 to be explicit about the bitwidth. */
96 struct jit_code_entry *relevant_entry;
97 struct jit_code_entry *first_entry;
100 /* GDB puts a breakpoint in this function. */
101 void MONO_NEVER_INLINE __jit_debug_register_code(void);
103 #if !defined(MONO_LLVM_LOADED) && defined(ENABLE_LLVM) && !defined(MONO_CROSS_COMPILE)
105 /* LLVM already defines these */
107 extern struct jit_descriptor __jit_debug_descriptor;
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__)
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 };
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;
132 mono_xdebug_init (const char *options)
137 args = g_strsplit (options, ",", -1);
138 for (ptr = args; ptr && *ptr; ptr ++) {
141 if (!strcmp (arg, "gdb"))
142 use_gdb_interface = TRUE;
143 if (!strcmp (arg, "save-symfiles"))
144 save_symfiles = TRUE;
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.");
155 if (use_gdb_interface)
159 xdebug_fp = fopen ("xdb.s", "w");
161 w = mono_img_writer_create (xdebug_fp, FALSE);
163 mono_img_writer_emit_start (w);
165 xdebug_writer = mono_dwarf_writer_create (w, il_file, 0, TRUE, TRUE);
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, "");
171 mono_dwarf_writer_emit_base_info (xdebug_writer, "JITted code", mono_unwind_get_cie_program ());
175 xdebug_begin_emit (MonoImageWriter **out_w, MonoDwarfWriter **out_dw)
180 w = mono_img_writer_create (NULL, TRUE);
182 mono_img_writer_emit_start (w);
184 /* This file will contain the IL code for methods which don't have debug info */
186 il_file = fopen ("xdb.il", "w");
188 dw = mono_dwarf_writer_create (w, il_file, il_file_line_index, FALSE, TRUE);
190 mono_dwarf_writer_emit_base_info (dw, "JITted code", mono_unwind_get_cie_program ());
197 xdebug_end_emit (MonoImageWriter *w, MonoDwarfWriter *dw, MonoMethod *method)
201 struct jit_code_entry *entry;
204 il_file_line_index = mono_dwarf_writer_get_il_file_line_index (dw);
205 mono_dwarf_writer_close (dw);
207 mono_img_writer_emit_writeout (w);
209 img = mono_img_writer_get_output (w, &img_size);
211 mono_img_writer_destroy (w);
214 /* Save the symbol files to help debugging */
217 static int file_counter;
220 file_name = g_strdup_printf ("xdb-%d.o", file_counter);
221 printf ("%s %p %d\n", file_name, img, img_size);
223 fp = fopen (file_name, "w");
224 fwrite (img, img_size, 1, fp);
229 /* Register the image with GDB */
231 entry = g_malloc0 (sizeof (struct jit_code_entry));
233 entry->symfile_addr = (const char*)img;
234 psize = (guint64*)&entry->symfile_size1;
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;
242 __jit_debug_descriptor.relevant_entry = entry;
243 __jit_debug_descriptor.action_flag = JIT_REGISTER_FN;
245 __jit_debug_register_code ();
251 * This could be called from inside gdb to flush the debugging information not yet
252 * registered with gdb.
255 mono_xdebug_flush (void)
258 xdebug_end_emit (xdebug_w, xdebug_writer, NULL);
260 xdebug_begin_emit (&xdebug_w, &xdebug_writer);
263 static int xdebug_method_count;
266 * mono_save_xdebug_info:
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.
273 mono_save_xdebug_info (MonoCompile *cfg)
275 MonoDebugMethodJitInfo *dmji;
277 if (use_gdb_interface) {
281 xdebug_syms = g_hash_table_new_full (g_str_hash, g_str_equal, g_free, NULL);
284 * gdb is not designed to handle 1000s of symbol files (one per method). So we
285 * group them into groups of 100.
287 if ((xdebug_method_count % 100) == 0)
288 mono_xdebug_flush ();
290 xdebug_method_count ++;
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);
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.
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);
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);
316 mono_loader_unlock ();
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);
327 mono_loader_unlock ();
333 * mono_save_trampoline_xdebug_info:
335 * Same as mono_save_xdebug_info, but for trampolines.
336 * LOCKING: Acquires the loader lock.
339 mono_save_trampoline_xdebug_info (MonoTrampInfo *info)
341 if (use_gdb_interface) {
345 /* This can be called before the loader lock is initialized */
346 mono_loader_lock_if_inited ();
348 xdebug_begin_emit (&w, &dw);
350 mono_dwarf_writer_emit_trampoline (dw, info->name, NULL, NULL, info->code, info->code_size, info->unwind_ops);
352 xdebug_end_emit (w, dw, NULL);
354 mono_loader_unlock_if_inited ();
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);
362 mono_loader_unlock_if_inited ();
366 #else /* !defined(DISABLE_AOT) && !defined(DISABLE_JIT) */
369 mono_xdebug_init (const char *options)
374 mono_save_xdebug_info (MonoCompile *cfg)
379 mono_save_trampoline_xdebug_info (MonoTrampInfo *info)