feat(asm): add RISC-V ELF relocatable object emission and SB relocation

support

parser/parser.go

@@ -398,10 +398,15 @@ func parseAddress(g []token.Token) ast.Address {
 		return addr
 	}
 	// Symbol-with-pseudo form: name[<>][+off](PSEUDO).
+	// When the prefix is not a valid symbol name (e.g. a bare number like
+	// 0(SP) in RISC-V), sym is nil and we fall through to regular memory
+	// operand parsing instead of returning an empty address.
 	if idx := findPseudoParen(g); idx >= 0 {
 		sym, _ := parseSymbolPrefix(g[:idx+3])
-		addr.Sym = sym
-		return addr
+		if sym != nil {
+			addr.Sym = sym
+			return addr
+		}
 	}
 
 	i := 0