misc: Serialize the ISA as a string in the checkpoint

With the introduction of multi-ISA gem5, we don't store the TARGET_ISA
anymore as a string in the root section of the checkpoint [1].  There is
therefore no way at the moment to asses the ISA of a CPU/ThreadContext.
This is a problem when it comes to checkpoint updates which are ISA
specific.

By explicitly serializing the ISA as a string under the cpu.isa section
we avoid this problem and we let cpt_upgraders be aware of the ISA in
use.

[1]: https://gem5-review.googlesource.com/c/public/gem5/+/48884

Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Change-Id: I1e75230cbc370cab84f4a54141b1e425af2dbfac
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>

src/arch/arm/isa.cc

@@ -80,7 +80,7 @@ RegClass floatRegClass(FloatRegClass, FloatRegClassName, 0, debug::FloatRegs);
 
 } // anonymous namespace
 
-ISA::ISA(const Params &p) : BaseISA(p), system(NULL),
+ISA::ISA(const Params &p) : BaseISA(p, "arm"), system(NULL),
     _decoderFlavor(p.decoderFlavor), pmu(p.pmu), impdefAsNop(p.impdef_nop)
 {
     _regClasses.push_back(&flatIntRegClass);
@@ -1541,6 +1541,8 @@ ISA::getCurSmeVecLenInBits() const
 void
 ISA::serialize(CheckpointOut &cp) const
 {
+    BaseISA::serialize(cp);
+
     DPRINTF(Checkpoint, "Serializing Arm Misc Registers\n");
     SERIALIZE_MAPPING(miscRegs, miscRegName, NUM_PHYS_MISCREGS);
 }

src/arch/generic/isa.hh

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020 ARM Limited
+ * Copyright (c) 2020, 2024 Arm Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
@@ -61,12 +61,16 @@ class BaseISA : public SimObject
     typedef std::vector<const RegClass *> RegClasses;
 
   protected:
-    using SimObject::SimObject;
+    BaseISA(const SimObjectParams &p, const std::string &name)
+      : SimObject(p), isaName(name)
+    {}
 
     ThreadContext *tc = nullptr;
 
     RegClasses _regClasses;
 
+    std::string isaName;
+
   public:
     virtual PCStateBase *newPCState(Addr new_inst_addr=0) const = 0;
     virtual void clear() {}
@@ -126,6 +130,12 @@ class BaseISA : public SimObject
     {
         globalClearExclusive();
     }
+
+    void
+    serialize(CheckpointOut &cp) const override
+    {
+        SERIALIZE_SCALAR(isaName);
+    }
 };
 
 } // namespace gem5

src/arch/mips/isa.cc

@@ -110,7 +110,7 @@ constexpr RegClass ccRegClass(CCRegClass, CCRegClassName, 0, debug::IntRegs);
 
 } // anonymous namespace
 
-ISA::ISA(const Params &p) : BaseISA(p), numThreads(p.num_threads),
+ISA::ISA(const Params &p) : BaseISA(p, "mips"), numThreads(p.num_threads),
     numVpes(p.num_vpes)
 {
     _regClasses.push_back(&intRegClass);

src/arch/power/isa.cc

@@ -62,7 +62,7 @@ RegClass ccRegClass(CCRegClass, CCRegClassName, 0, debug::IntRegs);
 
 } // anonymous namespace
 
-ISA::ISA(const Params &p) : BaseISA(p)
+ISA::ISA(const Params &p) : BaseISA(p, "power")
 {
     _regClasses.push_back(&intRegClass);
     _regClasses.push_back(&floatRegClass);

src/arch/riscv/isa.cc

@@ -256,7 +256,7 @@ RegClass ccRegClass(CCRegClass, CCRegClassName, 0, debug::IntRegs);
 
 } // anonymous namespace
 
-ISA::ISA(const Params &p) : BaseISA(p),
+ISA::ISA(const Params &p) : BaseISA(p, "riscv"),
     _rvType(p.riscv_type), checkAlignment(p.check_alignment),
     enableRvv(p.enable_rvv), vlen(p.vlen), elen(p.elen),
     _privilegeModeSet(p.privilege_mode_set)
@@ -792,6 +792,8 @@ ISA::setMiscReg(RegIndex idx, RegVal val)
 void
 ISA::serialize(CheckpointOut &cp) const
 {
+    BaseISA::serialize(cp);
+
     DPRINTF(Checkpoint, "Serializing Riscv Misc Registers\n");
     SERIALIZE_CONTAINER(miscRegFile);
 }

src/arch/sparc/isa.cc

@@ -79,7 +79,7 @@ RegClass ccRegClass(CCRegClass, CCRegClassName, 0, debug::IntRegs);
 
 } // anonymous namespace
 
-ISA::ISA(const Params &p) : BaseISA(p)
+ISA::ISA(const Params &p) : BaseISA(p, "sparc")
 {
     _regClasses.push_back(&flatIntRegClass);
     _regClasses.push_back(&floatRegClass);
@@ -844,6 +844,8 @@ ISA::setMiscReg(RegIndex idx, RegVal val)
 void
 ISA::serialize(CheckpointOut &cp) const
 {
+    BaseISA::serialize(cp);
+
     SERIALIZE_SCALAR(asi);
     SERIALIZE_SCALAR(tick);
     SERIALIZE_SCALAR(fprs);

src/arch/x86/isa.cc

@@ -152,7 +152,7 @@ RegClass matRegClass(MatRegClass, MatRegClassName, 0, debug::MatRegs);
 } // anonymous namespace
 
 ISA::ISA(const X86ISAParams &p)
-    : BaseISA(p), cpuid(new X86CPUID(p.vendor_string, p.name_string))
+    : BaseISA(p, "x86"), cpuid(new X86CPUID(p.vendor_string, p.name_string))
 {
     cpuid->addStandardFunc(FamilyModelStepping, p.FamilyModelStepping);
     cpuid->addStandardFunc(CacheParams, p.CacheParams);
@@ -491,6 +491,8 @@ ISA::setMiscReg(RegIndex idx, RegVal val)
 void
 ISA::serialize(CheckpointOut &cp) const
 {
+    BaseISA::serialize(cp);
+
     SERIALIZE_ARRAY(regVal, misc_reg::NumRegs);
 }