diff -Naur ocaml-3.10.0/asmrun/backtrace.c ocaml-3.10.0-backtrace/asmrun/backtrace.c
--- ocaml-3.10.0/asmrun/backtrace.c	2007-08-02 18:42:24.000000000 +0000
+++ ocaml-3.10.0-backtrace/asmrun/backtrace.c	2007-09-04 17:46:00.000000000 +0000
@@ -97,7 +97,7 @@
 
 /* Print a backtrace */
 
-static void print_location(int index, frame_descr * d)
+static int snprint_location(char *s, int len, int index, frame_descr * d)
 {
   uintnat infoptr;
   uint32 info1, info2, k, n, l, a, b;
@@ -106,7 +106,7 @@
   /* If no debugging information available, print nothing.
      When everything is compiled with -g, this corresponds to 
      compiler-inserted re-raise operations. */
-  if ((d->frame_size & 1) == 0) return;
+  if ((d->frame_size & 1) == 0) return 0;
   /* Recover debugging info */
   infoptr = ((uintnat) d +
              sizeof(char *) + sizeof(short) + sizeof(short) +
@@ -136,14 +136,60 @@
   else
     kind = "Called from";
 
-  fprintf(stderr, "%s file \"%s\", line %d, characters %d-%d\n",
-          kind, ((char *) infoptr) + n, l, a, b);
+  char *fmt = "%s file \"%s\", line %d, characters %d-%d\n";
+  if (s)
+    return snprintf(s, len, fmt, kind, ((char *) infoptr) + n, l, a, b);
+  else {
+    fprintf(stderr, fmt, kind, ((char *) infoptr) + n, l, a, b);
+    return 0;
+  }
 }
 
-void caml_print_exception_backtrace(void)
+static int snprint_exception_backtrace(char *s, int len)
 {
   int i;
 
+  int total_chars = 0;
   for (i = 0; i < caml_backtrace_pos; i++)
-    print_location(i, (frame_descr *) caml_backtrace_buffer[i]);
+  {
+    int chars = snprint_location(s, len, i, (frame_descr *) caml_backtrace_buffer[i]);
+    total_chars += chars;
+    s += chars;
+    len -= chars;
+  }
+  return total_chars;
+}
+
+void caml_print_exception_backtrace(void)
+{
+  snprint_exception_backtrace(0, 0);
+}
+
+CAMLprim value caml_sprint_backtrace(value sv)
+{
+  if (caml_backtrace_active)
+  {
+    int len = caml_string_length(sv);
+    char *s = String_val(sv);
+    int chars = snprint_exception_backtrace(s, len);
+    return Val_int(chars);
+  }
+  else
+    return Val_int(0);
+}
+
+CAMLprim value caml_capture_backtrace(value on)
+{
+  if (Bool_val(on))
+  {
+    caml_backtrace_active = 1;
+    caml_register_global_root(&caml_backtrace_last_exn);
+  }
+  else
+  {
+    caml_backtrace_active = 0;
+    caml_remove_global_root(&caml_backtrace_last_exn);
+    caml_backtrace_last_exn = Val_unit;
+  }
+  return Val_unit;
 }
diff -Naur ocaml-3.10.0/byterun/Makefile ocaml-3.10.0-backtrace/byterun/Makefile
--- ocaml-3.10.0/byterun/Makefile	2007-08-02 18:42:24.000000000 +0000
+++ ocaml-3.10.0-backtrace/byterun/Makefile	2007-08-02 19:25:23.000000000 +0000
@@ -29,7 +29,7 @@
 
 DOBJS=$(OBJS:.o=.d.o) instrtrace.d.o
 
-PRIMS=alloc.c array.c compare.c extern.c floats.c gc_ctrl.c hash.c \
+PRIMS=alloc.c array.c backtrace.c compare.c extern.c floats.c gc_ctrl.c hash.c \
   intern.c interp.c ints.c io.c lexing.c md5.c meta.c obj.c parsing.c \
   signals.c str.c sys.c terminfo.c callback.c weak.c finalise.c stacks.c \
   dynlink.c
diff -Naur ocaml-3.10.0/byterun/backtrace.c ocaml-3.10.0-backtrace/byterun/backtrace.c
--- ocaml-3.10.0/byterun/backtrace.c	2007-08-02 18:42:24.000000000 +0000
+++ ocaml-3.10.0-backtrace/byterun/backtrace.c	2007-09-04 17:46:00.000000000 +0000
@@ -168,7 +168,7 @@
 
 /* Print the location corresponding to the given PC */
 
-static void print_location(value events, int index)
+static int snprint_location(char *s, int len, value events, int index)
 {
    code_t pc = caml_backtrace_buffer[index];
   char * info;
@@ -177,7 +177,7 @@
   ev = event_for_location(events, pc);
   if (caml_is_instruction(*pc, RAISE)) {
     /* Ignore compiler-inserted raise */
-    if (ev == Val_false) return;
+    if (ev == Val_false) return 0;
     /* Initial raise if index == 0, re-raise otherwise */
     if (index == 0)
       info = "Raised at";
@@ -190,7 +190,13 @@
       info = "Called from";
   }
   if (ev == Val_false) {
-    fprintf(stderr, "%s unknown location\n", info);
+    char *fmt = "%s unknown location\n";
+    if (s)
+      return snprintf(s, len, fmt, info);
+    else {
+      fprintf(stderr, fmt, info);
+      return 0;
+    }
   } else {
     value ev_start = Field (Field (ev, EV_LOC), LOC_START);
     char *fname = String_val (Field (ev_start, POS_FNAME));
@@ -199,24 +205,74 @@
                    - Int_val (Field (ev_start, POS_BOL));
     int endchr = Int_val (Field (Field (Field (ev, EV_LOC), LOC_END), POS_CNUM))
                  - Int_val (Field (ev_start, POS_BOL));
-    fprintf (stderr, "%s file \"%s\", line %d, characters %d-%d\n", info, fname,
-             lnum, startchr, endchr);
+    char *fmt = "%s file \"%s\", line %d, characters %d-%d\n";
+    if (s)
+      return snprintf (s, len, fmt, info, fname, lnum, startchr, endchr);
+    else {
+      fprintf (stderr, fmt, info, fname,lnum, startchr, endchr);
+      return 0;
+    }
   }
 }
 
 /* Print a backtrace */
 
-CAMLexport void caml_print_exception_backtrace(void)
+static int snprint_exception_backtrace(char *s, int len)
 {
   value events;
   int i;
 
   events = read_debug_info();
   if (events == Val_false) {
-    fprintf(stderr,
-            "(Program not linked with -g, cannot print stack backtrace)\n");
-    return;
+    char *fmt = "(Program not linked with -g, cannot print stack backtrace)\n";
+    if (s)
+      return snprintf(s, len, fmt);
+    else {
+      fprintf(stderr, fmt);
+      return 0;
+    }
   }
+  int total_chars = 0;
   for (i = 0; i < caml_backtrace_pos; i++)
-    print_location(events, i);
+  {
+    int chars = snprint_location(s, len, events, i);
+    total_chars += chars;
+    s += chars;
+    len -= chars;
+  }
+  return total_chars;
+}
+
+CAMLexport void caml_print_exception_backtrace(void)
+{
+  snprint_exception_backtrace(0, 0);
+}
+
+CAMLprim value caml_sprint_backtrace(value sv)
+{
+  if (caml_backtrace_active)
+  {
+    int len = caml_string_length(sv);
+    char *s = String_val(sv);
+    int chars = snprint_exception_backtrace(s, len);
+    return Val_int(chars);
+  }
+  else
+    return Val_int(0);
+}
+
+CAMLprim value caml_capture_backtrace(value on)
+{
+  if (Bool_val(on))
+  {
+    caml_backtrace_active = 1;
+    caml_register_global_root(&caml_backtrace_last_exn);
+  }
+  else
+  {
+    caml_backtrace_active = 0;
+    caml_remove_global_root(&caml_backtrace_last_exn);
+    caml_backtrace_last_exn = Val_unit;
+  }
+  return Val_unit;
 }
diff -Naur ocaml-3.10.0/stdlib/printexc.ml ocaml-3.10.0-backtrace/stdlib/printexc.ml
--- ocaml-3.10.0/stdlib/printexc.ml	2007-03-30 20:30:16.000000000 +0000
+++ ocaml-3.10.0-backtrace/stdlib/printexc.ml	2007-09-04 18:53:36.000000000 +0000
@@ -13,6 +13,9 @@
 
 (* $Id: printexc.ml,v 1.18 2004/01/16 15:24:02 doligez Exp $ *)
 
+external capture_backtrace : bool -> unit = "caml_capture_backtrace";;
+external sprint_backtrace : string -> int = "caml_sprint_backtrace";;
+
 open Printf;;
 
 let locfmt = format_of_string "File \"%s\", line %d, characters %d-%d: %s";;
diff -Naur ocaml-3.10.0/stdlib/printexc.mli ocaml-3.10.0-backtrace/stdlib/printexc.mli
--- ocaml-3.10.0/stdlib/printexc.mli	2007-03-30 20:30:16.000000000 +0000
+++ ocaml-3.10.0-backtrace/stdlib/printexc.mli	2007-09-04 18:28:58.000000000 +0000
@@ -15,6 +15,16 @@
 
 (** Facilities for printing exceptions. *)
 
+(* UNCOMMENT
+val capture_backtrace : bool -> unit
+(** [Printexc.capture_backtrace b] turns the capturing of backtraces
+   on if [b] is true, otherwise turns it off. *)
+
+val sprint_backtrace : string -> int
+(** [Printexc.sprint_backtrace s] prints the latest exception
+   backtrace into [s] and returns the number of characters written. *)
+*)
+
 val to_string : exn -> string
 (** [Printexc.to_string e] returns a string representation of
    the exception [e]. *)