load.c: fix `prev_ext_config` clobbering in `require_internal`

The variable `prev_ext_config` is modified by `ext_config_push` between
`setjmp` and `longjmp` calls. Since `ext_config_push` and `ext_config_pop`
are small and likely to be inlined, `prev_ext_config` can be allocated on
a register and get clobbered. Fix by making it `volatile`.

This bug can be observed by adding a check for values greater than 1 in
`th2->ext_config.ractor_safe` after `ext_config_pop` and building with Clang.

1 files changed, 3 insertions, 3 deletions

diff --git a/load.c b/load.c
index 329b0f4b3b..017c236483 100644
--- a/load.c
+++ b/load.c
@@ -1346,14 +1346,14 @@ rb_resolve_feature_path(VALUE klass, VALUE fname)
 }
 
 static void
-ext_config_push(rb_thread_t *th, struct rb_ext_config *prev)
+ext_config_push(rb_thread_t *th, volatile struct rb_ext_config *prev)
 {
     *prev = th->ext_config;
     th->ext_config = (struct rb_ext_config){0};
 }
 
 static void
-ext_config_pop(rb_thread_t *th, struct rb_ext_config *prev)
+ext_config_pop(rb_thread_t *th, volatile struct rb_ext_config *prev)
 {
     th->ext_config = *prev;
 }
@@ -1407,7 +1407,7 @@ require_internal(rb_execution_context_t *ec, VALUE fname, int exception, bool wa
     VALUE realpaths = get_loaded_features_realpaths(vm_ns);
     VALUE realpath_map = get_loaded_features_realpath_map(vm_ns);
     volatile bool reset_ext_config = false;
-    struct rb_ext_config prev_ext_config;
+    volatile struct rb_ext_config prev_ext_config;
 
     path = rb_str_encode_ospath(fname);
     RUBY_DTRACE_HOOK(REQUIRE_ENTRY, RSTRING_PTR(fname));