fix(asm): close the oracle parity gaps in frame addressing and calls

asm/assemble.go

@@ -515,6 +515,9 @@ func addSP(size int) []byte { // ADDQ $size, SP
 func instrSize(s *ast.Instr, fi frameInfo, long bool, link *linkInfo) (int, error) {
 	mnem := strings.ToUpper(s.Mnemonic.Text)
 	if isJumpMnemonic(mnem) {
+		if (mnem == "CALL" || mnem == "JMP") && isSBCall(s) {
+			return 5, nil // opcode + rel32, always the long form
+		}
 		return jumpSize(mnem, long), nil
 	}
 	code, _, err := encodeInstr(s, 0, nil, fi, false, nil, link)
@@ -564,9 +567,10 @@ func encodeInstr(s *ast.Instr, pc int, offsets map[string]int, fi frameInfo, lon
 	var ps []sbPatch
 	var err error
 	if isJumpMnemonic(mnem) {
-		if mnem == "CALL" && isSBCall(s) {
-			// CALL sym(SB): a rel32 call against a static or external
-			// symbol, resolved by the file-level layout or the linker.
+		if (mnem == "CALL" || mnem == "JMP") && isSBCall(s) {
+			// CALL/JMP sym(SB): a rel32 call (or tail call) against a
+			// static or external symbol, resolved by the file-level layout
+			// or the linker.
 			code, ps, err = encodeSBCall(s, link)
 			if err != nil {
 				return nil, nil, err
@@ -678,8 +682,12 @@ func encodeSBCall(s *ast.Instr, link *linkInfo) ([]byte, []sbPatch, error) {
 	if !ok {
 		return nil, nil, fmt.Errorf("CALL: unsupported operand")
 	}
+	opcode := []byte{0xE8}
+	if strings.ToUpper(s.Mnemonic.Text) == "JMP" {
+		opcode = []byte{0xE9} // a tail call, no return address pushed
+	}
 	e := &enc{}
-	if err := e.emit(&instr{opcode: []byte{0xE8}, modrm: -1, sib: -1, disp: le32(0), sb: &sbRef{name: m.name, addend: m.addend}}); err != nil {
+	if err := e.emit(&instr{opcode: opcode, modrm: -1, sib: -1, disp: le32(0), sb: &sbRef{name: m.name, addend: m.addend}}); err != nil {
 		return nil, nil, err
 	}
 	ps := make([]sbPatch, len(e.patches))