Remove excessive stack usage in caml_get_exception_raw_backtrace

stedolan · stedolan · commit 846ce834e5df · 2019-05-14T16:05:10.000+01:00
diff --git a/runtime/backtrace.c b/runtime/backtrace.c
@@ -136,34 +136,21 @@ CAMLprim value caml_get_exception_raw_backtrace(value unit)
   CAMLparam0();
   CAMLlocal1(res);
 
-  /* Beware: the allocations below may cause finalizers to be run, and another
-     backtrace---possibly of a different length---to be stashed (for example
-     if the finalizer raises then catches an exception).  We choose to ignore
-     any such finalizer backtraces and return the original one. */
-
   if (!caml_backtrace_active ||
       caml_backtrace_buffer == NULL ||
       caml_backtrace_pos == 0) {
     res = caml_alloc(0, 0);
   }
   else {
-    backtrace_slot saved_caml_backtrace_buffer[BACKTRACE_BUFFER_SIZE];
-    int saved_caml_backtrace_pos;
     intnat i;
 
-    saved_caml_backtrace_pos = caml_backtrace_pos;
-
-    if (saved_caml_backtrace_pos > BACKTRACE_BUFFER_SIZE) {
-      saved_caml_backtrace_pos = BACKTRACE_BUFFER_SIZE;
-    }
-
-    memcpy(saved_caml_backtrace_buffer, caml_backtrace_buffer,
-           saved_caml_backtrace_pos * sizeof(backtrace_slot));
-
-    res = caml_alloc(saved_caml_backtrace_pos, 0);
-    for (i = 0; i < saved_caml_backtrace_pos; i++) {
-      Field(res, i) = Val_backtrace_slot(saved_caml_backtrace_buffer[i]);
+    /* We use caml_alloc_shr instead of caml_alloc, since caml_alloc might
+       trigger finalisers, which in turn might overwrite the backtrace. */
+    res = caml_alloc_shr(caml_backtrace_pos, 0);
+    for (i = 0; i < caml_backtrace_pos; i++) {
+      caml_initialize(&Field(res, i), Val_backtrace_slot(caml_backtrace_buffer[i]));
     }
+    res = caml_check_urgent_gc(res);
   }
 
   CAMLreturn(res);
