cmd/link: add loadelf support for riscv64

Update #36641

Change-Id: I8618da30d8940a56d6cc86a37a2f54b31ee029e5
Reviewed-on: https://go-review.googlesource.com/c/go/+/263601
Trust: Joel Sing <joel@sing.id.au>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Joel Sing <joel@sing.id.au>
TryBot-Result: Go Bot <gobot@golang.org>

src/cmd/link/internal/loadelf/ldelf.go

@@ -372,6 +372,11 @@ func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, f *bio.Reader,
 			return errorf("elf object but not ppc64")
 		}
 
+	case sys.RISCV64:
+		if mach != elf.EM_RISCV || class != elf.ELFCLASS64 {
+			return errorf("elf object but not riscv64")
+		}
+
 	case sys.S390X:
 		if mach != elf.EM_S390 || class != elf.ELFCLASS64 {
 			return errorf("elf object but not s390x")
@@ -946,14 +951,15 @@ func relSize(arch *sys.Arch, pn string, elftype uint32) (uint8, error) {
 	// performance.
 
 	const (
-		AMD64  = uint32(sys.AMD64)
-		ARM    = uint32(sys.ARM)
-		ARM64  = uint32(sys.ARM64)
-		I386   = uint32(sys.I386)
-		PPC64  = uint32(sys.PPC64)
-		S390X  = uint32(sys.S390X)
-		MIPS   = uint32(sys.MIPS)
-		MIPS64 = uint32(sys.MIPS64)
+		AMD64   = uint32(sys.AMD64)
+		ARM     = uint32(sys.ARM)
+		ARM64   = uint32(sys.ARM64)
+		I386    = uint32(sys.I386)
+		MIPS    = uint32(sys.MIPS)
+		MIPS64  = uint32(sys.MIPS64)
+		PPC64   = uint32(sys.PPC64)
+		RISCV64 = uint32(sys.RISCV64)
+		S390X   = uint32(sys.S390X)
 	)
 
 	switch uint32(arch.Family) | elftype<<16 {
@@ -1056,6 +1062,27 @@ func relSize(arch *sys.Arch, pn string, elftype uint32) (uint8, error) {
 		S390X | uint32(elf.R_390_GOT64)<<16,
 		S390X | uint32(elf.R_390_PLT64)<<16:
 		return 8, nil
+
+	case RISCV64 | uint32(elf.R_RISCV_RVC_BRANCH)<<16,
+		RISCV64 | uint32(elf.R_RISCV_RVC_JUMP)<<16:
+		return 2, nil
+
+	case RISCV64 | uint32(elf.R_RISCV_32)<<16,
+		RISCV64 | uint32(elf.R_RISCV_BRANCH)<<16,
+		RISCV64 | uint32(elf.R_RISCV_HI20)<<16,
+		RISCV64 | uint32(elf.R_RISCV_LO12_I)<<16,
+		RISCV64 | uint32(elf.R_RISCV_LO12_S)<<16,
+		RISCV64 | uint32(elf.R_RISCV_GOT_HI20)<<16,
+		RISCV64 | uint32(elf.R_RISCV_PCREL_HI20)<<16,
+		RISCV64 | uint32(elf.R_RISCV_PCREL_LO12_I)<<16,
+		RISCV64 | uint32(elf.R_RISCV_PCREL_LO12_S)<<16,
+		RISCV64 | uint32(elf.R_RISCV_RELAX)<<16:
+		return 4, nil
+
+	case RISCV64 | uint32(elf.R_RISCV_64)<<16,
+		RISCV64 | uint32(elf.R_RISCV_CALL)<<16,
+		RISCV64 | uint32(elf.R_RISCV_CALL_PLT)<<16:
+		return 8, nil
 	}
 }