arch-power: Refactor argument registers

This reintroduces the argument register constants that
were removed in commit 7bb456f02 ("arch-power: Delete
unused register related constants"), adds a definition
for the sixth argument register and switches to these
constants to specify the arguments used by the system
call ABI.

Change-Id: I5804f4d2b27a04d0e7b69132e5abce5761b239f5
Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40938
Reviewed-by: Boris Shingarov <shingarov@labware.com>
Maintainer: Boris Shingarov <shingarov@labware.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/power/regs/int.hh

@@ -43,6 +43,12 @@ const int NumIntRegs = NumIntArchRegs + NumIntSpecialRegs;
 
 // Semantically meaningful register indices
 const int ReturnValueReg = 3;
+const int ArgumentReg0 = 3;
+const int ArgumentReg1 = 4;
+const int ArgumentReg2 = 5;
+const int ArgumentReg3 = 6;
+const int ArgumentReg4 = 7;
+const int ArgumentReg5 = 8;
 const int StackPointerReg = 1;
 
 enum MiscIntRegNums

src/arch/power/se_workload.cc

@@ -31,7 +31,12 @@ namespace PowerISA
 {
 
 const std::vector<int> SEWorkload::SyscallABI::ArgumentRegs = {
-    3, 4, 5, 6, 7, 8
+    ArgumentReg0,
+    ArgumentReg1,
+    ArgumentReg2,
+    ArgumentReg3,
+    ArgumentReg4,
+    ArgumentReg5
 };
 
 } // namespace PowerISA