View source for DWARF4 Line Table File Numbers

'''DWARF4'''

'''DWARF4 Line Table File Numbers'''

There is no self-contradiction here.

DW_AT_decl_file Sec 2.14 Declaration Coordinates page 50.
   The value of the DW_AT_decl_file attribute corresponds to a
   file number from the line number information table for the
   compilation unit containing the debugging information entry
   and represents the source file in which the declaration
   appeared (see Section 6.2 on page 148). The value 0
   indicates that no source file has been specified.

DW_LNS_set_file Defined in sec 6.2.5.2 page 119.
   Stores the file value into the file register of the state
   machine.  
   [comment: Nothing is said about 0 meaning no source file.]

DW_MACINFO_start_file Section 6.3.1.2 page 124.
   This index corresponds to a file number in the line
   number information table for the relevant compilation unit.
   [comment: Nothing is said about 0 meaning no source file.]

Table 6.2.2 state machine registers page 109
file  
   An unsigned integer indicating the identity of
   the source file corresponding to a machine
   instruction. 
   [comment: While not stated it is clear this
   refers to the line table header file table.]
   [comment: Nothing is said about 0 meaning no source file.]
    
Section 6.2.2 Page 111 
initial state of the registers
file  1
   [comment; Nothing is said on why 1 is appropriate here.]
   [comment: Seemingly there is an assumption that the file
   table has at least one entry, and that first
   entry is numbered 1 and is the primary source file.]
   [comment: Nothing is said about 0 meaning no source file.]

Section 6.2.4 page 115
   The primary source file is described by an entry whose
   path name exactly matches that given in the DW_AT_name
   attribute in the compilation unit, and whose directory is
   understood to be given by the implicit entry with index 0.

   The line number program assigns numbers to each of the
   file entries in order, beginning with 1, and uses those
   numbers instead of file names in the file register.

   [comment: nothing stops a DWARF4 compiler from emitting
   an initial file with the name of the primary source file.
   And having the 'file register' default to 1 suggests
   stronly that it is advisable for compiler writers to add
   this source file name first. Thus having consistency
   with the initial state of the registers].

   The line number program assigns numbers to each of the
   file entries in order, beginning with 1, and uses those
   numbers instead of file names in the file register.