Merge branch 'fix-stack-alignment'

compiler/jit-encoder.stanza

@@ -1286,6 +1286,7 @@ defn AsmGen (code:CodeHolder,
   ;   before the CALL instruction.
   ;2) Therefore we need to push an odd number of items onto the stack to
   ;   ensure that our own CALL instructions are 16-byte aligned.
+  ;   In the body of JIT generated code, RSP will be 0x???????0. 
   defn make-jit-launch-stub () :
     ;Save incoming arguments
     push(a, reg(Tmp1))                 ;Save Dummy for 16-byte stack alignment.
@@ -1445,9 +1446,13 @@ defn AsmGen (code:CodeHolder,
   ;Call directly using the C-calling convention.
   defn emit-fast-callc (f:VMImm, xs:Tuple<Local|VMType>, ys:Tuple<VMImm>) :
     ;This is added to CRSP before the call.
+    ;In the body of JIT generated code, launcher ensures that RSP will be 0x???????0. 
+    ;The System-V convention requires that RSP by 0x???????0 before the CALL instruction.
+    ;Therefore we ensure that the number of slots is even.
     defn crsp-offset (records:CallCRecords) -> Int :
       val num-slots = num-mem-args(records) + c-num-spill-slots(backend)
-      (8 * num-slots + 7) & -8
+      ;Ensure that the number of slots is even so that the new C RSP is 16-byte aligned.
+      8 * ((num-slots + 1) & -2)
 
     ;Compute all the SetCArg to implement the given calling records.
     defn compute-set-c-args (records:CallCRecords) -> Tuple<SetCArg> :