feat(asm): encode indirect JMP and CALL on all four architectures

Assisted-by: GLM 5.3 Flash

asm/encode_test.go

@@ -181,6 +181,39 @@ func TestControl(t *testing.T) {
 	checkOp(t, x86asm.JBE, "JLS", Imm(0))
 }
 
+// TestIndirectControlFlow pins the indirect JMP/CALL forms: FF /4 for JMP and
+// FF /2 for CALL through a register or memory.  A REX appears only for the
+// extended registers, never REX.W: the branch operand size is fixed at 64
+// bits in long mode.
+func TestIndirectControlFlow(t *testing.T) {
+	cases := []struct {
+		name string
+		mnem string
+		ops  []Operand
+		want string
+	}{
+		{"JMP AX", "JMP", []Operand{AX}, "ffe0"},
+		{"CALL AX", "CALL", []Operand{AX}, "ffd0"},
+		{"JMP (BX)", "JMP", []Operand{Ptr(BX, 0, 8)}, "ff23"},
+		{"CALL (BX)", "CALL", []Operand{Ptr(BX, 0, 8)}, "ff13"},
+		{"JMP 8(BX)", "JMP", []Operand{Ptr(BX, 8, 8)}, "ff6308"},
+		{"CALL -16(BX)", "CALL", []Operand{Ptr(BX, -16, 8)}, "ff53f0"},
+		{"JMP R8", "JMP", []Operand{Reg{idx: 8, size: 2}}, "41ffe0"},
+		{"CALL R9", "CALL", []Operand{Reg{idx: 9, size: 2}}, "41ffd1"},
+		{"JMP R15", "JMP", []Operand{Reg{idx: 15, size: 2}}, "41ffe7"},
+	}
+	for _, c := range cases {
+		code, err := Encode(c.mnem, c.ops...)
+		if err != nil {
+			t.Errorf("%s: %v", c.name, err)
+			continue
+		}
+		if got := fmt.Sprintf("%x", code); got != c.want {
+			t.Errorf("%s: got %s, want %s", c.name, got, c.want)
+		}
+	}
+}
+
 // TestSSEMoveGroundTruth checks the legacy (non-VEX) SSE moves byte for byte
 // against the Go assembler.  wantOp is the decoder's name, which differs from
 // the Plan 9 spelling for the octa moves (MOVOU = MOVDQU, MOVO = MOVDQA).