External section symbol reference.
XREF s ymbol[,symbol,...,symbol]
The XREF directive is used to specify that the list of symbols is referenced in the current section, but is not defined within the current section. These symbols must either have been defined outside of any section or declared as globally accessible within another section using the XDEF directive. If the XREF directive is not used to specify that a symbol is defined globally and the symbol is not defined within the current section, an error is generated, and all references within the current section to such a symbol are flagged as undefined. The XREF directive must appear before any reference to symbol in the section.
A label is not allowed with this directive.
SECTION FILTER
XREF AA,CC,DD
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ENDSEC