From e7a3693d02be3c8e4718fb008b5f5e9a9612c410 Mon Sep 17 00:00:00 2001 From: Taylor R Campbell Date: Thu, 31 Mar 2022 01:55:08 +0000 Subject: [PATCH 19/49] libc/atomic: Fix membars in __atomic_load/store_* stubs. - membar_enter/exit ordering was backwards. - membar_enter doesn't make any sense for load anyway. - Switch to membar_release for store and membar_acquire for load. The only sensible orderings for a simple load or store are acquire or release, respectively, or sequential consistency. This never provided correct sequential consistency before -- we should really make it conditional on memmodel but I don't know offhand what the values of memmodel might be and this is at least better than before. --- common/lib/libc/atomic/atomic_load.c | 3 +-- common/lib/libc/atomic/atomic_store.c | 3 +-- 2 files changed, 2 insertions(+), 4 deletions(-) diff --git a/common/lib/libc/atomic/atomic_load.c b/common/lib/libc/atomic/atomic_load.c index a93bc0ee4ea0..c19d2074ba96 100644 --- a/common/lib/libc/atomic/atomic_load.c +++ b/common/lib/libc/atomic/atomic_load.c @@ -40,9 +40,8 @@ uint ## b ## _t \ __atomic_load_ ## n(const volatile void *ptr, int memmodel) \ { \ uint## b ##_t val; \ - membar_enter(); \ val = *(const volatile uint ## b ## _t *)ptr; \ - membar_exit(); \ + membar_acquire(); \ return val; \ } diff --git a/common/lib/libc/atomic/atomic_store.c b/common/lib/libc/atomic/atomic_store.c index 474bb43b8ba9..cf53ae83010c 100644 --- a/common/lib/libc/atomic/atomic_store.c +++ b/common/lib/libc/atomic/atomic_store.c @@ -40,9 +40,8 @@ void \ __atomic_store_ ## n(volatile void *ptr, uint ## b ## _t val, \ int memmodel) \ { \ - membar_enter(); \ + membar_release(); \ *(volatile uint ## b ## _t *)ptr = val; \ - membar_exit(); \ } atomic_store_n(1, 8)