Add FFLAG support in csr-relative instuctions

Author: 2011eric

emulate.c

@@ -639,7 +639,10 @@ static uint32_t csr_csrrw(struct riscv_t *rv, uint32_t csr, uint32_t val)
     if (!c)
         return 0;
 
-    const uint32_t out = *c;
+    uint32_t out = *c;
+    if (csr == CSR_FFLAGS)
+        out &= FFLAG_MASK;
+
     if (csr_is_writable(csr))
         *c = val;
 
@@ -670,7 +673,10 @@ static uint32_t csr_csrrc(struct riscv_t *rv, uint32_t csr, uint32_t val)
     if (!c)
         return 0;
 
-    const uint32_t out = *c;
+    uint32_t out = *c;
+    if (csr == CSR_FFLAGS)
+        out &= FFLAG_MASK;
+
     if (csr_is_writable(csr))
         *c &= ~val;
     return out;