feat(asm): encode the riscv64 privileged instructions

Assisted-by: GLM 5.3 Flash

asm/riscv_encode_test.go

@@ -7,6 +7,8 @@ import (
 	"bytes"
 	"encoding/binary"
 	"encoding/hex"
+	"os"
+	"path/filepath"
 	"strings"
 	"testing"
 
@@ -785,6 +787,50 @@ TEXT ·sys(SB), NOSPLIT, $0
 	}
 }
 
+// TestRISCV_privilegedWords pins the privileged ISA slice.  The toolchain's
+// object table carries the encodings (its assembler accepts no mnemonic for
+// them), so the golden vectors come from the privileged and debug
+// specifications: SFENCEVMA X10, X11 is 0x12b50073, SRET 0x10200073,
+// MRET 0x30200073, WFI 0x10500073 and DRET 0x7b200073.
+func TestRISCV_privilegedWords(t *testing.T) {
+	fn := firstTextRISCV(t, `#include "textflag.h"
+TEXT ·priv(SB), NOSPLIT, $0
+	SFENCEVMA	X10, X11
+	SRET
+	MRET
+	WFI
+	DRET
+	RET
+`)
+	code := assembleRISCVHelper(t, fn)
+	riscvWants(t, code,
+		0x12B50073, // sfence.vma x10, x11
+		0x10200073, // sret
+		0x30200073, // mret
+		0x10500073, // wfi
+		0x7B200073, // dret
+	)
+}
+
+// TestRISCV_privilegedAliases checks the supervisor spellings SCALL and
+// SBREAK against the toolchain: both alias ECALL and EBREAK and must come
+// out byte-identical.
+func TestRISCV_privilegedAliases(t *testing.T) {
+	src := `#include "textflag.h"
+
+TEXT ·alias(SB), NOSPLIT, $0
+	SCALL
+	SBREAK
+	RET
+`
+	dir := t.TempDir()
+	path := filepath.Join(dir, "alias_riscv64.s")
+	if err := os.WriteFile(path, []byte(src), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	assertRISCVDifferential(t, path, src, "alias")
+}
+
 func TestRISCV_MOV_sym_FP(t *testing.T) {
 	// MOV $sym(FP), rd lowers to the frame-adjusted ADDI against SP: the
 	// toolchain's argframe spelling.  A zero frame leaves the offset at the