string is the new file name. In general, the filename is
recognized whether or not it is surrounded by quotes "; but if you wish
to specify an empty file name, you must give the quotes–
statement may go away in future: it is only recognized to be compatible with
old as programs.
When emitting DWARF2 line number information,
.file assigns filenames
.debug_line file name table. The syntax is:
.file fileno filename
The fileno operand should be a unique positive integer to use as the index of the entry in the table. The filename operand is a C string literal.
The detail of filename indices is exposed to the user because the filename
table is shared with the
.debug_info section of the DWARF2 debugging
information, and thus the user must know the exact indices that table
entries will have.