diff options
Diffstat (limited to 'include/gcc/x86_64/ck_pr.h')
| -rw-r--r-- | include/gcc/x86_64/ck_pr.h | 35 |
1 files changed, 28 insertions, 7 deletions
diff --git a/include/gcc/x86_64/ck_pr.h b/include/gcc/x86_64/ck_pr.h index 532d593f277c7..4de1332910cee 100644 --- a/include/gcc/x86_64/ck_pr.h +++ b/include/gcc/x86_64/ck_pr.h @@ -58,8 +58,8 @@ #endif /* - * Prevent speculative execution in busy-wait loops (P4 <=) - * or "predefined delay". + * Prevent speculative execution in busy-wait loops (P4 <=) or "predefined + * delay". */ CK_CC_INLINE static void ck_pr_stall(void) @@ -75,18 +75,39 @@ ck_pr_stall(void) __asm__ __volatile__(I ::: "memory"); \ } -CK_PR_FENCE(atomic, "sfence") -CK_PR_FENCE(atomic_store, "sfence") -CK_PR_FENCE(atomic_load, "mfence") -CK_PR_FENCE(store_atomic, "sfence") -CK_PR_FENCE(load_atomic, "mfence") +/* Atomic operations are always serializing. */ +CK_PR_FENCE(atomic, "") +CK_PR_FENCE(atomic_store, "") +CK_PR_FENCE(atomic_load, "") +CK_PR_FENCE(store_atomic, "") +CK_PR_FENCE(load_atomic, "") + +/* Traditional fence interface. */ CK_PR_FENCE(load, "lfence") CK_PR_FENCE(load_store, "mfence") CK_PR_FENCE(store, "sfence") CK_PR_FENCE(store_load, "mfence") CK_PR_FENCE(memory, "mfence") + +/* Below are stdatomic-style fences. */ + +/* + * Provides load-store and store-store ordering. However, Intel specifies that + * the WC memory model is relaxed. It is likely an sfence *is* sufficient (in + * particular, stores are not re-ordered with respect to prior loads and it is + * really just the stores that are subject to re-ordering). However, we take + * the conservative route as the manuals are too ambiguous for my taste. + */ CK_PR_FENCE(release, "mfence") + +/* + * Provides load-load and load-store ordering. The lfence instruction ensures + * all prior load operations are complete before any subsequent instructions + * actually begin execution. However, the manual also ends up going to describe + * WC memory as a relaxed model. + */ CK_PR_FENCE(acquire, "mfence") + CK_PR_FENCE(acqrel, "mfence") CK_PR_FENCE(lock, "mfence") CK_PR_FENCE(unlock, "mfence") |