Help with NIF upgrade implementation

I observe a reproducible SEGV of the 21.3.8.4 VM on macos Catalina when
repeatedly recompiling a module that has a skeletal NIF with an upgrade
callback.  The skeleton is based on the examples in the documentation
but I am assuming that I have made an error somewhere. I would be
grateful for any pointers.

The very simple NIF library is attached, together with its makefile and
the Erlang module's source. Once built, the failure is seen very
quickly:

$ erl
Erlang/OTP 21 [erts-10.3.5.3] [source] [64-bit] [smp:12:12] [ds:12:12:10] [async-threads:1] [hipe]

Eshell V10.3.5.3 (abort with ^G)
1> c(rtc), rtc:foo(), rtc:bar().
ok
2> c(rtc), rtc:foo(), rtc:bar().
ok
3> c(rtc), rtc:foo(), rtc:bar().
Segmentation fault: 11
$

The stack is

* thread #10, name = '6_scheduler', stop reason = EXC_BAD_ACCESS (code=1, address=0x70)
frame #0: 0x000000001e41bc0e beam.smp`nif_resource_dtor at atomic.h:240
237 ETHR_AINT_T__ tmp;
238
239 tmp = incr;
-> 240 __asm__ __volatile__(
241 "lock; xadd" ETHR_AINT_SUFFIX__ " %0, %1" /* xadd didn't exist prior to the 486 */
242 : "=r"(tmp)
243 : "m"(var->counter), "0"(tmp)

* thread #10, name = '6_scheduler', stop reason = EXC_BAD_ACCESS (code=1, address=0x70)
* frame #0: 0x000000001e41bc0e beam.smp`nif_resource_dtor at atomic.h:240
frame #1: 0x000000001e41bc07 beam.smp`nif_resource_dtor
frame #2: 0x000000001e41bc07 beam.smp`nif_resource_dtor
frame #3: 0x000000001e41bc07 beam.smp`nif_resource_dtor
frame #4: 0x000000001e41bc07 beam.smp`nif_resource_dtor
frame #5: 0x000000001e41bbf0 beam.smp`nif_resource_dtor(bin=0x000000001fc800f8)
frame #6: 0x000000001e3d390d beam.smp`sweep_off_heap(p=0x0000000020740778, fullsweep=<unavailable>) at erl_binary.h:453
frame #7: 0x000000001e3d73f7 beam.smp`do_minor(p=0x0000000020740778, live_hf_end=<unavailable>, mature=<unavailable>, mature_size=696, new_sz=376, objv=<unavailable>, nobj=3) at erl_gc.c:1674
frame #8: 0x000000001e3d9af4 beam.smp`garbage_collect(p=0x0000000020740778, live_hf_end=0xfffffffffffffff8, need=4, objv=0x000000001f7d4440, nobj=3, fcalls=3047, max_young_gen_usage=0) at erl_gc.c:1417
frame #9: 0x000000001e3dabb5 beam.smp`erts_garbage_collect_nobump(p=0x0000000020740778, need=<unavailable>, objv=<unavailable>, nobj=<unavailable>, fcalls=3047) at erl_gc.c:878
frame #10: 0x000000001e4e8097 beam.smp`process_main(x_reg_array=0x000000001f7d4440, f_reg_array=<unavailable>) at beam_hot.h:104
frame #11: 0x000000001e287916 beam.smp`sched_thread_func(vesdp=0x0000000020bb3400) at erl_process.c:8469
frame #12: 0x000000001e4cbd52 beam.smp`thr_wrapper(vtwd=0x00007ffee197c140) at ethread.c:118
frame #13: 0x00007fff692aa109 libsystem_pthread.dylib`_pthread_start + 148
frame #14: 0x00007fff692a5b8b libsystem_pthread.dylib`thread_start + 15

Robert Harris

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#include <assert.h>
#include <stdlib.h>
#include <erl_nif.h>

static int rtc_load(ErlNifEnv *, void **, ERL_NIF_TERM);
static void rtc_resource_destroy(ErlNifEnv *, void *);
static int rtc_upgrade(ErlNifEnv *, void **, void **, ERL_NIF_TERM);
static ERL_NIF_TERM foo(ErlNifEnv *, int, const ERL_NIF_TERM[]);
static ERL_NIF_TERM bar(ErlNifEnv *, int, const ERL_NIF_TERM[]);

static ErlNifFunc api[] = {
	{ "foo", 0, foo, 0 },
	{ "bar", 0, bar, 0 },
};
ERL_NIF_INIT(rtc, api, &rtc_load, NULL, &rtc_upgrade, NULL);

static ErlNifResourceType *rtc_resource;

static int
rtc_load(ErlNifEnv *env, void **priv_data, ERL_NIF_TERM nif_context)
{
	rtc_resource = enif_open_resource_type(env, NULL, "rtc",
	    rtc_resource_destroy, ERL_NIF_RT_CREATE | ERL_NIF_RT_TAKEOVER,
	    NULL);
        assert(rtc_resource != NULL);
	return (0);
}

static void
rtc_resource_destroy(ErlNifEnv *env, void *obj)
{
}

static int
rtc_upgrade(ErlNifEnv *env, void **priv_data, void **old_priv_data,
    ERL_NIF_TERM load_info)
{
	return (0);
}

static ERL_NIF_TERM
foo(ErlNifEnv *env, int argc, const ERL_NIF_TERM argv[])
{
	void **resource;
	ERL_NIF_TERM result;

	resource = enif_alloc_resource(rtc_resource, sizeof (void *));
	assert(resource != NULL);
	result = enif_make_resource(env, resource);
	enif_release_resource(resource);
	return (result);
}

static ERL_NIF_TERM
bar(ErlNifEnv *env, int argc, const ERL_NIF_TERM argv[])
{
        return (enif_make_atom(env, "ok"));
}