stack-limit: bug: not handling RLIM_INFINITY.

* gc.c (gc_init): We must check rlim_cur for the RLIM_INFINITY
value indicating unlimited stack, and not misuse this value as a
limit number, otherwise hilarity ensues. This reproduced on
an older platform with make 3.81, which calls setrlimit to
bring about an unlimited stack, passed on to child processes.
Because of this txr segfaulted, as a consequence of a false
positive.

* tests/012/stack.tl (stack-limited): New variable which
indicates whether there is a stack limit. If there isn't, we
avoid running the fork-based test case. Also, we set the stack
limit to 32768 so we have a limit against which to run some of
the tests.

2 files changed, 10 insertions, 7 deletions

diff --git a/gc.c b/gc.c
index 4b7c0a8c..ee47f054 100644
--- a/gc.c
+++ b/gc.c
@@ -896,7 +896,7 @@ void gc_init(val *stack_bottom)
 #if HAVE_RLIMIT
   struct rlimit rl;
   if (getrlimit(RLIMIT_STACK, &rl) == 0) {
-    if (rl.rlim_cur > 512 * 1024) {
+    if (rl.rlim_cur != RLIM_INFINITY && rl.rlim_cur > 512 * 1024) {
       rlim_t lim = (rl.rlim_cur - rl.rlim_cur / 16) / sizeof (val);
       gc_stack_limit = gc_stack_bottom - lim;
     }
diff --git a/tests/012/stack.tl b/tests/012/stack.tl
index 879d3d27..9a7534bb 100644
--- a/tests/012/stack.tl
+++ b/tests/012/stack.tl
@@ -1,5 +1,7 @@
 (load "../common")
 
+(defvar stack-limited (set-stack-limit 32768))
+
 (defun recur () (recur))
 
 (defmacro so (expr)
@@ -8,12 +10,13 @@
 
 (test (so (recur)) :so)
 
-(test (let ((pid (fork)))
-        (cond
-          ((zerop pid) (set-stack-limit 0) (recur))
-          (t (let ((status (wait pid)))
-               (w-ifsignaled status)))))
-      t)
+(if stack-limited
+  (test (let ((pid (fork)))
+          (cond
+            ((zerop pid) (set-stack-limit 0) (recur))
+            (t (let ((status (wait pid)))
+                 (w-ifsignaled status)))))
+        t))
 
 (defmacro infexp ()
   ^(foo (infexp)))