There are two different versions of the
.file directive. Targets
that support DWARF2 line number information use the DWARF2 version of
.file. Other targets use the default version.
This version of the
.file directive tells as that we
are about to start a new logical file. The syntax is:
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.