[LLDB][RISCV] Add RISC-V ArchSpec and rv32/rv64 variant detection

Adds the RISC-V ArchSpec bits contributed by @simoncook as part of D62732,
plus logic to distinguish between riscv32 and riscv64 based on ELF class.

The patch follows the implementation approach previously used for MIPS.
It defines RISC-V architecture subtypes and inspects the ELF header,
namely the ELF class, to detect the right subtype.

Differential Revision: https://reviews.llvm.org/D86292

lldb/include/lldb/Utility/ArchSpec.h

@@ -92,6 +92,12 @@ public:
     eARM_abi_hard_float = 0x00000400
   };
 
+  enum RISCVSubType {
+    eRISCVSubType_unknown,
+    eRISCVSubType_riscv32,
+    eRISCVSubType_riscv64,
+  };
+
   enum Core {
     eCore_arm_generic,
     eCore_arm_armv4,
@@ -184,6 +190,9 @@ public:
     eCore_hexagon_hexagonv4,
     eCore_hexagon_hexagonv5,
 
+    eCore_riscv32,
+    eCore_riscv64,
+
     eCore_uknownMach32,
     eCore_uknownMach64,
 

lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp

@@ -296,9 +296,23 @@ static uint32_t mipsVariantFromElfFlags (const elf::ELFHeader &header) {
   return arch_variant;
 }
 
+static uint32_t riscvVariantFromElfFlags(const elf::ELFHeader &header) {
+  uint32_t fileclass = header.e_ident[EI_CLASS];
+  switch (fileclass) {
+  case llvm::ELF::ELFCLASS32:
+    return ArchSpec::eRISCVSubType_riscv32;
+  case llvm::ELF::ELFCLASS64:
+    return ArchSpec::eRISCVSubType_riscv64;
+  default:
+    return ArchSpec::eRISCVSubType_unknown;
+  }
+}
+
 static uint32_t subTypeFromElfHeader(const elf::ELFHeader &header) {
   if (header.e_machine == llvm::ELF::EM_MIPS)
     return mipsVariantFromElfFlags(header);
+  else if (header.e_machine == llvm::ELF::EM_RISCV)
+    return riscvVariantFromElfFlags(header);
 
   return LLDB_INVALID_CPUTYPE;
 }

lldb/source/Utility/ArchSpec.cpp

@@ -212,6 +212,11 @@ static const CoreDefinition g_core_definitions[] = {
     {eByteOrderLittle, 4, 4, 4, llvm::Triple::hexagon,
      ArchSpec::eCore_hexagon_hexagonv5, "hexagonv5"},
 
+    {eByteOrderLittle, 4, 2, 4, llvm::Triple::riscv32, ArchSpec::eCore_riscv32,
+     "riscv32"},
+    {eByteOrderLittle, 8, 2, 4, llvm::Triple::riscv64, ArchSpec::eCore_riscv64,
+     "riscv64"},
+
     {eByteOrderLittle, 4, 4, 4, llvm::Triple::UnknownArch,
      ArchSpec::eCore_uknownMach32, "unknown-mach-32"},
     {eByteOrderLittle, 8, 4, 4, llvm::Triple::UnknownArch,
@@ -395,6 +400,10 @@ static const ArchDefinitionEntry g_elf_arch_entries[] = {
      0xFFFFFFFFu, 0xFFFFFFFFu}, // ARC
     {ArchSpec::eCore_avr, llvm::ELF::EM_AVR, LLDB_INVALID_CPUTYPE,
      0xFFFFFFFFu, 0xFFFFFFFFu}, // AVR
+    {ArchSpec::eCore_riscv32, llvm::ELF::EM_RISCV,
+     ArchSpec::eRISCVSubType_riscv32, 0xFFFFFFFFu, 0xFFFFFFFFu}, // riscv32
+    {ArchSpec::eCore_riscv64, llvm::ELF::EM_RISCV,
+     ArchSpec::eRISCVSubType_riscv64, 0xFFFFFFFFu, 0xFFFFFFFFu}, // riscv64
 };
 
 static const ArchDefinition g_elf_arch_def = {

lldb/test/Shell/ObjectFile/ELF/riscv-arch.yaml

@@ -0,0 +1,24 @@
+# RUN: yaml2obj --docnum=1 %s > %t32
+# RUN: yaml2obj --docnum=2 %s > %t64
+# RUN: lldb-test object-file %t32 | FileCheck --check-prefix=CHECK-RV32 %s
+# RUN: lldb-test object-file %t64 | FileCheck --check-prefix=CHECK-RV64 %s
+
+# CHECK-RV32: Architecture: riscv32--
+
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS32
+  Data:            ELFDATA2LSB
+  Type:            ET_EXEC
+  Machine:         EM_RISCV
+...
+
+# CHECK-RV64: Architecture: riscv64--
+
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_EXEC
+  Machine:         EM_RISCV
+...