target/xtensa: implement exclusive access option

The Exclusive Instructions provide a general-purpose mechanism for
atomic updates of memory-based synchronization variables that can be
used for exclusion algorithms.

Use cmpxchg-based implementation that is sufficient for the typical use
of exclusive access in atomic operations.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/target/xtensa/cpu.h b/target/xtensa/cpu.h
index 8301923..28a6fb4 100644
--- a/target/xtensa/cpu.h
+++ b/target/xtensa/cpu.h
@@ -527,6 +527,8 @@ typedef struct CPUXtensaState {
     } fregs[16];
     float_status fp_status;
     uint32_t windowbase_next;
+    uint32_t exclusive_addr;
+    uint32_t exclusive_val;
 
 #ifndef CONFIG_USER_ONLY
     xtensa_tlb_entry itlb[7][MAX_TLB_WAY_SIZE];