bugfix: gc-incorrect creation of catenated stream.

* stream.c (make_catenated_stream): Fix incorrect order
of operations: list of streams stored into a structure
that is not yet visible to the garbage collector.
(Rules for coding this properly are explained in
HACKING.) This was found by running a test with --gc-debug
on 64 bit Darwin. The read_eval_stream function calls
make_catenated_stream with an argument that is freshly
constructed in the argument expression itself, triggering
the issue.

1 files changed, 4 insertions, 1 deletions

diff --git a/stream.c b/stream.c
index b34da981..398feaf6 100644
--- a/stream.c
+++ b/stream.c
@@ -2343,9 +2343,12 @@ static struct strm_ops cat_stream_ops =
 val make_catenated_stream(val stream_list)
 {
   struct cat_strm *s = coerce(struct cat_strm *, chk_malloc(sizeof *s));
+  val catstrm = nil;
   strm_base_init(&s->a);
+  s->streams = nil;
+  catstrm = cobj(coerce(mem_t *, s), stream_s, &cat_stream_ops.cobj_ops);
   s->streams = stream_list;
-  return cobj(coerce(mem_t *, s), stream_s, &cat_stream_ops.cobj_ops);
+  return catstrm;
 }
 
 val make_catenated_stream_v(struct args *streams)