Merge pull request #13 from ved-rivos/enc_clarifications

encoding clarifications

cfi_backward.adoc

@@ -34,6 +34,8 @@ using the `mop.r` and `mop.rr` instructions defined by the Zimops extension.
 |            2+^|`12`                2+^|`5`     2+^|`3`      2+^|`5`    2+^|`7`      
 |===
 
+Encoding `rs1` as `x0` is not supported for `sspush`.
+Encoding `rd`  as `x0` is not supported for `sspop`.
 
 [width=100%]
 [%header, cols="6,<3,>3,<3,>3,<3,>3,<3,>3,<3,>3,<3,>3", grid=rows, frame=none]
@@ -45,6 +47,8 @@ using the `mop.r` and `mop.rr` instructions defined by the Zimops extension.
 |            2+^|`7`       2+^|`5`   2+^|`5`     2+^|`3`      2+^|`5`    2+^|`7`      
 |===
 
+Encoding `rd` as `x0` is not supported for `ssamoswap`.
+
 When `menvcfg.CFI` is 0, then Zisslpcfi is not enabled for privilege modes less than
 M and backward-edge CFI is not active at privilege levels less than M.
 
@@ -125,7 +129,7 @@ using shadow stacks is as follows:
          :
          : 
         sspop x5       # pop from shadow stack into x5
-        sschkra x1, x5 # compare link register x1 to shadow 
+        sschkra x5, x1 # compare link register x1 to shadow 
                        # link register x5; faults if not same
         ret