Simplify backtrace mechanism; fix #3633 #3634 #3644

Instead of preserving a backtrace in `mrb_state`, `mrb_exc_set`
keeps packed backtrace in an exception object. `#backtrace` unpacks
it to an array of strings.

6 files changed, 90 insertions, 283 deletions

diff --git a/src/backtrace.c b/src/backtrace.c
index 75f926b2e..5081f1809 100644
--- a/src/backtrace.c
+++ b/src/backtrace.c
@@ -14,83 +14,24 @@
 #include <mruby/error.h>
 #include <mruby/numeric.h>
 
-struct backtrace_location_raw {
-  int i;
-  int lineno;
-  const char *filename;
-  mrb_sym method_id;
-};
-
 struct backtrace_location {
-  int i;
   int lineno;
   const char *filename;
-  const char *method;
-};
-
-typedef void (*each_backtrace_func)(mrb_state*, struct backtrace_location_raw*, void*);
-typedef void (*output_stream_func)(mrb_state*, struct backtrace_location*, void*);
-
-#ifndef MRB_DISABLE_STDIO
-
-struct print_backtrace_args {
-  FILE *stream;
-  int tracehead;
+  mrb_sym method_id;
 };
 
-static void
-print_backtrace_i(mrb_state *mrb, struct backtrace_location *loc, void *data)
-{
-  struct print_backtrace_args *args;
-
-  args = (struct print_backtrace_args*)data;
-
-  if (args->tracehead) {
-    fprintf(args->stream, "trace:\n");
-    args->tracehead = FALSE;
-  }
-
-  fprintf(args->stream, "\t[%d] %s:%d", loc->i, loc->filename, loc->lineno);
-
-  if (loc->method) {
-    fprintf(args->stream, ":in %s", loc->method);
-  }
-
-  fprintf(args->stream, "\n");
-}
-
-#endif
-
-static void
-get_backtrace_i(mrb_state *mrb, struct backtrace_location *loc, void *data)
-{
-  mrb_value ary, str;
-  int ai = mrb_gc_arena_save(mrb);
-
-  ary = mrb_obj_value((struct RArray*)data);
-
-  str = mrb_str_new_cstr(mrb, loc->filename);
-  str = mrb_format(mrb, "%S:%S", str, mrb_fixnum_to_str(mrb, mrb_fixnum_value(loc->lineno), 10));
-
-  if (loc->method) {
-    mrb_str_cat_lit(mrb, str, ":in ");
-    mrb_str_cat_cstr(mrb, str, loc->method);
-  }
-
-  mrb_ary_push(mrb, ary, str);
-  mrb_gc_arena_restore(mrb, ai);
-}
+typedef void (*each_backtrace_func)(mrb_state*, int i, struct backtrace_location*, void*);
 
 static void
 each_backtrace(mrb_state *mrb, mrb_int ciidx, mrb_code *pc0, each_backtrace_func func, void *data)
 {
-  int i;
+  int i, j;
 
   if (ciidx >= mrb->c->ciend - mrb->c->cibase)
     ciidx = 10; /* ciidx is broken... */
 
-  for (i = ciidx; i >= 0; i--) {
-    struct backtrace_location_raw loc;
+  for (i=ciidx, j=0; i >= 0; i--,j++) {
+    struct backtrace_location loc;
     mrb_callinfo *ci;
     mrb_irep *irep;
     mrb_code *pc;
@@ -122,58 +63,11 @@ each_backtrace(mrb_state *mrb, mrb_int ciidx, mrb_code *pc0, each_backtrace_func
     }
 
     loc.method_id = ci->mid;
-    loc.i = i;
-    func(mrb, &loc, data);
-  }
-}
-
-struct output_backtrace_args {
-  output_stream_func func;
-  void *data;
-};
-
-static void
-output_backtrace_i(mrb_state *mrb, struct backtrace_location_raw *loc_raw, void *data)
-{
-  struct backtrace_location loc;
-  struct output_backtrace_args *args = (struct output_backtrace_args *)data;
-
-  loc.i          = loc_raw->i;
-  loc.lineno     = loc_raw->lineno;
-  loc.filename   = loc_raw->filename;
-  loc.method     = mrb_sym2name(mrb, loc_raw->method_id);
-
-  args->func(mrb, &loc, args->data);
-}
-
-static void
-output_backtrace(mrb_state *mrb, mrb_int ciidx, mrb_code *pc0, output_stream_func func, void *data)
-{
-  struct output_backtrace_args args;
-  args.func = func;
-  args.data = data;
-  each_backtrace(mrb, ciidx, pc0, output_backtrace_i, &args);
-}
-
-static void
-exc_output_backtrace(mrb_state *mrb, struct RObject *exc, output_stream_func func, void *stream)
-{
-  mrb_value lastpc;
-  mrb_code *code;
-
-  lastpc = mrb_obj_iv_get(mrb, exc, mrb_intern_lit(mrb, "lastpc"));
-  if (mrb_nil_p(lastpc)) {
-    code = NULL;
+    func(mrb, j, &loc, data);
   }
-  else {
-    code = (mrb_code*)mrb_cptr(lastpc);
-  }
-
-  output_backtrace(mrb, mrb_fixnum(mrb_obj_iv_get(mrb, exc, mrb_intern_lit(mrb, "ciidx"))),
-                   code, func, stream);
 }
 
-/* mrb_print_backtrace/mrb_get_backtrace:
+/* mrb_print_backtrace
 
    function to retrieve backtrace information from the exception.
    note that if you call method after the exception, call stack will be
@@ -202,19 +96,27 @@ print_backtrace(mrb_state *mrb, mrb_value backtrace)
 }
 
 static void
-print_backtrace_saved(mrb_state *mrb)
+print_packed_backtrace(mrb_state *mrb, mrb_value packed)
 {
-  int i, ai;
   FILE *stream = stderr;
+  struct backtrace_location *bt;
+  mrb_int n, i;
 
-  fprintf(stream, "trace:\n");
-  ai = mrb_gc_arena_save(mrb);
-  for (i = 0; i < mrb->backtrace.n; i++) {
-    mrb_backtrace_entry *entry;
-
-    entry = &(mrb->backtrace.entries[i]);
-    fprintf(stream, "\t[%d] %s:%d", i, entry->filename, entry->lineno);
+  if (!mrb_string_p(packed)) {
+  broken:
+    mrb_raise(mrb, E_RUNTIME_ERROR, "broken backtrace");
+  }
+  n = RSTRING_LEN(packed);
+  if (n%sizeof(struct backtrace_location) != 0) goto broken;
+  n /= sizeof(struct backtrace_location);
+  bt = (struct backtrace_location*)RSTRING_PTR(packed);
 
+  fprintf(stream, "trace:\n");
+  for (i = 0; i < n; i++) {
+    int ai = mrb_gc_arena_save(mrb);
+    struct backtrace_location *entry = &bt[i];
+    if (entry->filename == NULL) continue;
+    fprintf(stream, "\t[%d] %s:%d", (int)i, entry->filename, entry->lineno);
     if (entry->method_id != 0) {
       const char *method_name;
 
@@ -222,7 +124,6 @@ print_backtrace_saved(mrb_state *mrb)
       fprintf(stream, ":in %s", method_name);
       mrb_gc_arena_restore(mrb, ai);
     }
-
     fprintf(stream, "\n");
   }
 }
@@ -237,20 +138,13 @@ mrb_print_backtrace(mrb_state *mrb)
   }
 
   backtrace = mrb_obj_iv_get(mrb, mrb->exc, mrb_intern_lit(mrb, "backtrace"));
-  if (!mrb_nil_p(backtrace)) {
+  if (mrb_array_p(backtrace)) {
     print_backtrace(mrb, backtrace);
   }
-  else if (mrb->backtrace.n > 0) {
-    print_backtrace_saved(mrb);
-  }
   else {
-    struct print_backtrace_args args;
-    args.stream = stderr;
-    args.tracehead = TRUE;
-    exc_output_backtrace(mrb, mrb->exc, print_backtrace_i, (void*)&args);
+    print_packed_backtrace(mrb, backtrace);
   }
 }
-
 #else
 
 MRB_API void
@@ -260,126 +154,83 @@ mrb_print_backtrace(mrb_state *mrb)
 
 #endif
 
-MRB_API mrb_value
-mrb_exc_backtrace(mrb_state *mrb, mrb_value self)
-{
-  mrb_value ary;
-
-  ary = mrb_ary_new(mrb);
-  exc_output_backtrace(mrb, mrb_obj_ptr(self), get_backtrace_i, (void*)mrb_ary_ptr(ary));
-
-  return ary;
-}
-
-MRB_API mrb_value
-mrb_get_backtrace(mrb_state *mrb)
-{
-  mrb_value ary;
-  mrb_callinfo *ci = mrb->c->ci;
-  mrb_code *pc = ci->pc;
-  mrb_int ciidx = (mrb_int)(ci - mrb->c->cibase - 1);
-
-  if (ciidx < 0) ciidx = 0;
-  ary = mrb_ary_new(mrb);
-  output_backtrace(mrb, ciidx, pc, get_backtrace_i, (void*)mrb_ary_ptr(ary));
-
-  return ary;
-}
-
-void
-mrb_free_backtrace(mrb_state *mrb)
-{
-  mrb->backtrace.exc = 0;
-  mrb->backtrace.n = 0;
-  mrb->backtrace.n_allocated = 0;
-  mrb_free(mrb, mrb->backtrace.entries);
-}
-
 static void
-save_backtrace_i(mrb_state *mrb,
-                 struct backtrace_location_raw *loc_raw,
+pack_backtrace_i(mrb_state *mrb,
+                 int i,
+                 struct backtrace_location *loc,
                  void *data)
 {
-  mrb_backtrace_entry *entry;
-
-  if (mrb->backtrace.n >= mrb->backtrace.n_allocated) {
-    int new_n_allocated;
-    if (mrb->backtrace.n_allocated == 0) {
-      new_n_allocated = 8;
-    }
-    else {
-      new_n_allocated = mrb->backtrace.n_allocated * 2;
-    }
-    mrb->backtrace.entries = (mrb_backtrace_entry *)
-      mrb_realloc(mrb,
-                  mrb->backtrace.entries,
-                  sizeof(mrb_backtrace_entry) * new_n_allocated);
-    mrb->backtrace.n_allocated = new_n_allocated;
-  }
-
-  entry = &mrb->backtrace.entries[mrb->backtrace.n];
-  entry->filename  = loc_raw->filename;
-  entry->lineno    = loc_raw->lineno;
-  entry->method_id = loc_raw->method_id;
+  struct backtrace_location *entry = (struct backtrace_location*)data;
 
-  mrb->backtrace.n++;
+  entry[i] = *loc;
 }
 
-void
-mrb_save_backtrace(mrb_state *mrb)
+static mrb_value
+packed_backtrace(mrb_state *mrb)
 {
-  mrb_value lastpc;
-  mrb_code *code;
-  mrb_int ciidx;
-
-  mrb->backtrace.n = 0;
-  mrb->backtrace.exc = 0;
-
-  if (!mrb->exc)
-    return;
-
-  mrb->backtrace.exc = mrb->exc;
-
-  lastpc = mrb_obj_iv_get(mrb, mrb->exc, mrb_intern_lit(mrb, "lastpc"));
-  if (mrb_nil_p(lastpc)) {
-    code = NULL;
-  }
-  else {
-    code = (mrb_code*)mrb_cptr(lastpc);
-  }
-
-  ciidx = mrb_fixnum(mrb_obj_iv_get(mrb, mrb->exc, mrb_intern_lit(mrb, "ciidx")));
-
-  each_backtrace(mrb, ciidx, code, save_backtrace_i, NULL);
+  mrb_value backtrace;
+  mrb_int ciidx = mrb->c->ci - mrb->c->cibase;
+  mrb_int len = (ciidx+1)*sizeof(struct backtrace_location);
+  char *ptr;
+
+  backtrace = mrb_str_new(mrb, NULL, len);
+  ptr = RSTRING_PTR(backtrace);
+  memset(ptr, 0, len);
+  each_backtrace(mrb, ciidx, mrb->c->ci->pc, pack_backtrace_i, ptr);
+  return backtrace;
 }
 
-mrb_value
-mrb_restore_backtrace(mrb_state *mrb)
+void
+mrb_keep_backtrace(mrb_state *mrb, mrb_value exc)
 {
-  int i;
   mrb_value backtrace;
+  int ai = mrb_gc_arena_save(mrb);
 
-  backtrace = mrb_ary_new(mrb);
-  for (i = 0; i < mrb->backtrace.n; i++) {
-    int ai;
-    mrb_backtrace_entry *entry;
-    mrb_value mrb_entry;
-
-    ai = mrb_gc_arena_save(mrb);
-    entry = &(mrb->backtrace.entries[i]);
+  backtrace = packed_backtrace(mrb);
+  mrb_iv_set(mrb, exc, mrb_intern_lit(mrb, "backtrace"), backtrace);
+  mrb_gc_arena_restore(mrb, ai);
+}
 
-    mrb_entry = mrb_format(mrb, "%S:%S",
-                           mrb_str_new_cstr(mrb, entry->filename),
-                           mrb_fixnum_value(entry->lineno));
+mrb_value
+mrb_unpack_backtrace(mrb_state *mrb, mrb_value backtrace)
+{
+  mrb_value str;
+  struct backtrace_location *bt;
+  mrb_int n, i;
+
+  if (mrb_array_p(backtrace)) return backtrace;
+  if (!mrb_string_p(backtrace)) {
+  broken:
+    mrb_raise(mrb, E_RUNTIME_ERROR, "broken backtrace");
+  }
+  str = backtrace;
+  n = RSTRING_LEN(str);
+  if (n%sizeof(struct backtrace_location) != 0) goto broken;
+  n /= sizeof(struct backtrace_location);
+  bt = (struct backtrace_location*)RSTRING_PTR(str);
+  backtrace = mrb_ary_new_capa(mrb, n);
+  for (i = 0; i < n; i++) {
+    int ai = mrb_gc_arena_save(mrb);
+    struct backtrace_location *entry = &bt[i];
+    mrb_value btline;
+
+    if (entry->filename == NULL) continue;
+    btline = mrb_format(mrb, "%S:%S",
+                              mrb_str_new_cstr(mrb, entry->filename),
+                              mrb_fixnum_value(entry->lineno));
     if (entry->method_id != 0) {
-      mrb_str_cat_lit(mrb, mrb_entry, ":in ");
-      mrb_str_cat_cstr(mrb, mrb_entry, mrb_sym2name(mrb, entry->method_id));
+      mrb_str_cat_lit(mrb, btline, ":in ");
+      mrb_str_cat_cstr(mrb, btline, mrb_sym2name(mrb, entry->method_id));
     }
-
-    mrb_ary_push(mrb, backtrace, mrb_entry);
-
+    mrb_ary_push(mrb, backtrace, btline);
     mrb_gc_arena_restore(mrb, ai);
   }
 
   return backtrace;
 }
+
+mrb_value
+mrb_get_backtrace(mrb_state *mrb)
+{
+  return mrb_unpack_backtrace(mrb, packed_backtrace(mrb));
+}
diff --git a/src/error.c b/src/error.c
index 5bb547afe..b71c718e2 100644
--- a/src/error.c
+++ b/src/error.c
@@ -163,8 +163,8 @@ exc_inspect(mrb_state *mrb, mrb_value exc)
   return str;
 }
 
-void mrb_save_backtrace(mrb_state *mrb);
-mrb_value mrb_restore_backtrace(mrb_state *mrb);
+void mrb_keep_backtrace(mrb_state *mrb, mrb_value exc);
+mrb_value mrb_unpack_backtrace(mrb_state *mrb, mrb_value backtrace);
 
 static mrb_value
 exc_get_backtrace(mrb_state *mrb, mrb_value exc)
@@ -175,17 +175,9 @@ exc_get_backtrace(mrb_state *mrb, mrb_value exc)
   attr_name = mrb_intern_lit(mrb, "backtrace");
   backtrace = mrb_iv_get(mrb, exc, attr_name);
   if (!mrb_array_p(backtrace)) {
-    if (mrb_obj_ptr(exc) == mrb->backtrace.exc && mrb->backtrace.n > 0) {
-      backtrace = mrb_restore_backtrace(mrb);
-      mrb->backtrace.n = 0;
-      mrb->backtrace.exc = 0;
-    }
-    else {
-      backtrace = mrb_exc_backtrace(mrb, exc);
-    }
+    backtrace = mrb_unpack_backtrace(mrb, backtrace);
     mrb_iv_set(mrb, exc, attr_name, backtrace);
   }
-
   return backtrace;
 }
 
@@ -224,7 +216,6 @@ exc_debug_info(mrb_state *mrb, struct RObject *exc)
   mrb_callinfo *ci = mrb->c->ci;
   mrb_code *pc = ci->pc;
 
-  mrb_obj_iv_set(mrb, exc, mrb_intern_lit(mrb, "ciidx"), mrb_fixnum_value((mrb_int)(ci - mrb->c->cibase)));
   while (ci >= mrb->c->cibase) {
     mrb_code *err = ci->err;
 
@@ -245,36 +236,9 @@ exc_debug_info(mrb_state *mrb, struct RObject *exc)
   }
 }
 
-static mrb_bool
-have_backtrace(mrb_state *mrb, struct RObject *exc)
-{
-  return !mrb_nil_p(mrb_obj_iv_get(mrb, exc, mrb_intern_lit(mrb, "backtrace")));
-}
-
 void
 mrb_exc_set(mrb_state *mrb, mrb_value exc)
 {
-  if (!mrb->gc.out_of_memory && mrb->backtrace.n > 0) {
-    mrb_value target_exc = mrb_nil_value();
-    int ai;
-
-    ai = mrb_gc_arena_save(mrb);
-    if ((mrb->exc && !have_backtrace(mrb, mrb->exc))) {
-      target_exc = mrb_obj_value(mrb->exc);
-    }
-    else if (!mrb_nil_p(exc) && mrb->backtrace.exc) {
-      target_exc = mrb_obj_value(mrb->backtrace.exc);
-      mrb_gc_protect(mrb, target_exc);
-    }
-    if (!mrb_nil_p(target_exc)) {
-      mrb_value backtrace;
-      backtrace = mrb_restore_backtrace(mrb);
-      set_backtrace(mrb, target_exc, backtrace);
-    }
-    mrb_gc_arena_restore(mrb, ai);
-  }
-
-  mrb->backtrace.n = 0;
   if (mrb_nil_p(exc)) {
     mrb->exc = 0;
   }
@@ -282,7 +246,7 @@ mrb_exc_set(mrb_state *mrb, mrb_value exc)
     mrb->exc = mrb_obj_ptr(exc);
     if (!mrb->gc.out_of_memory) {
       exc_debug_info(mrb, mrb->exc);
-      mrb_save_backtrace(mrb);
+      mrb_keep_backtrace(mrb, exc);
     }
   }
 }
diff --git a/src/gc.c b/src/gc.c
index bd633a9fe..7337c659a 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -735,8 +735,6 @@ obj_free(mrb_state *mrb, struct RBasic *obj, int end)
 
   case MRB_TT_EXCEPTION:
     mrb_gc_free_iv(mrb, (struct RObject*)obj);
-    if ((struct RObject*)obj == mrb->backtrace.exc)
-      mrb->backtrace.exc = 0;
     break;
 
   case MRB_TT_CLASS:
@@ -870,8 +868,6 @@ root_scan_phase(mrb_state *mrb, mrb_gc *gc)
   mrb_gc_mark(mrb, (struct RBasic*)mrb->top_self);
   /* mark exception */
   mrb_gc_mark(mrb, (struct RBasic*)mrb->exc);
-  /* mark backtrace */
-  mrb_gc_mark(mrb, (struct RBasic*)mrb->backtrace.exc);
   /* mark pre-allocated exception */
   mrb_gc_mark(mrb, (struct RBasic*)mrb->nomem_err);
   mrb_gc_mark(mrb, (struct RBasic*)mrb->stack_err);
diff --git a/src/kernel.c b/src/kernel.c
index c1300ed70..f0a5ed536 100644
--- a/src/kernel.c
+++ b/src/kernel.c
@@ -872,7 +872,6 @@ mrb_f_raise(mrb_state *mrb, mrb_value self)
     /* fall through */
   default:
     exc = mrb_make_exception(mrb, argc, a);
-    mrb_obj_iv_set(mrb, mrb_obj_ptr(exc), mrb_intern_lit(mrb, "lastpc"), mrb_cptr_value(mrb, mrb->c->ci->pc));
     mrb_exc_raise(mrb, exc);
     break;
   }
diff --git a/src/state.c b/src/state.c
index 2a02debef..0be5a184a 100644
--- a/src/state.c
+++ b/src/state.c
@@ -246,7 +246,6 @@ mrb_close(mrb_state *mrb)
 
   /* free */
   mrb_gc_free_gv(mrb);
-  mrb_free_backtrace(mrb);
   mrb_free_context(mrb, mrb->root_c);
   mrb_free_symtbl(mrb);
   mrb_alloca_free(mrb);
diff --git a/src/vm.c b/src/vm.c
index b56da6c88..896be7ad9 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -1741,8 +1741,6 @@ RETRY_TRY_BLOCK:
 
       L_RAISE:
         ci0 = ci = mrb->c->ci;
-        mrb_obj_iv_ifnone(mrb, mrb->exc, mrb_intern_lit(mrb, "lastpc"), mrb_cptr_value(mrb, pc));
-        mrb_obj_iv_ifnone(mrb, mrb->exc, mrb_intern_lit(mrb, "ciidx"), mrb_fixnum_value(ci - mrb->c->cibase));
         eidx = ci->eidx;
         if (ci == mrb->c->cibase) {
           if (ci->ridx == 0) goto L_STOP;