Clear p->fvalue when handling a try/catch

p->fvalue will be set by BIFs that generate exceptions
(such as throw/1), and it will not be cleared before another
exception is generated. Potentially, p->fvalue may contain a
huge term (e.g. after throw(HugeTerm)) which will be kept in
the heap.

We can shorten the lifetime of f->value by clearing it in
the instructions that handle catches: catch_end and try_end.
That is safe because BEAM code will never access p->fvalue.
If BEAM code needs to rethrow an exception it will use a
reference to the value passed in an X register.

The reason that p->fvalue must not be cleared already in
handle_error() is that native code trap handlers will use
it. (See the comment before handle_error() and the comment
at the end of handle_error() in beam_emu.c for some more
information about exception handling.)

1 files changed, 2 insertions, 0 deletions

diff --git a/erts/emulator/beam/beam_emu.c b/erts/emulator/beam/beam_emu.c
index 311bb94242..a90e6a0ba8 100644
--- a/erts/emulator/beam/beam_emu.c
+++ b/erts/emulator/beam/beam_emu.c
@@ -1814,6 +1814,7 @@ void process_main(Eterm * x_reg_array, FloatDef* f_reg_array)
      c_p->catches--;
      make_blank(yb(Arg(0)));
      if (is_non_value(r(0))) {
+         c_p->fvalue = NIL;
 	 if (x(1) == am_throw) {
 	     r(0) = x(2);
 	 } else {
@@ -1843,6 +1844,7 @@ void process_main(Eterm * x_reg_array, FloatDef* f_reg_array)
      c_p->catches--;
      make_blank(yb(Arg(0)));
      if (is_non_value(r(0))) {
+         c_p->fvalue = NIL;
 	 r(0) = x(1);
 	 x(1) = x(2);
 	 x(2) = x(3);