arch-arm: Add a reverse map MiscRegIndex -> MiscRegNum64

Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Change-Id: I63cdcdfca610cfd37a03769e077388a193510bc7
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/55606
Reviewed-by: Richard Cooper <richard.cooper@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/arm/regs/misc.cc

@@ -1454,6 +1454,10 @@ std::bitset<NUM_MISCREG_INFOS> miscRegInfo[NUM_MISCREGS]; // initialized below
 
 namespace {
 
+// The map is translating a MiscRegIndex into AArch64 system register
+// numbers (op0, op1, crn, crm, op2)
+std::unordered_map<MiscRegIndex, MiscRegNum64> idxToMiscRegNum;
+
 // The map is translating AArch64 system register numbers
 // (op0, op1, crn, crm, op2) into a MiscRegIndex
 std::unordered_map<MiscRegNum64, MiscRegIndex> miscRegNumToIdx{
@@ -1947,6 +1951,17 @@ decodeAArch64SysReg(unsigned op0, unsigned op1,
     }
 }
 
+MiscRegNum64
+encodeAArch64SysReg(MiscRegIndex misc_reg)
+{
+    if (auto it = idxToMiscRegNum.find(misc_reg);
+        it != idxToMiscRegNum.end()) {
+        return it->second;
+    } else {
+        panic("Invalid MiscRegIndex: %n\n", misc_reg);
+    }
+}
+
 void
 ISA::initializeMiscRegMetadata()
 {
@@ -4585,6 +4600,12 @@ ISA::initializeMiscRegMetadata()
     // DBGDTRTX_EL0 -> DBGDTRRXint
     // MDCR_EL3 -> SDCR, NAM D7-2108 (the latter is unimpl. in gem5)
 
+    // Populate the idxToMiscRegNum map
+    assert(idxToMiscRegNum.empty());
+    for (const auto& [key, val] : miscRegNumToIdx) {
+        idxToMiscRegNum.insert({val, key});
+    }
+
     completed = true;
 }
 

src/arch/arm/regs/misc.hh

@@ -1199,6 +1199,8 @@ namespace ArmISA
     MiscRegIndex decodeAArch64SysReg(unsigned op0, unsigned op1,
                                      unsigned crn, unsigned crm,
                                      unsigned op2);
+    MiscRegNum64 encodeAArch64SysReg(MiscRegIndex misc_reg);
+
     // Whether a particular AArch64 system register is -always- read only.
     bool aarch64SysRegReadOnly(MiscRegIndex miscReg);