DWARF Standard


HOME
SPECIFICATIONS
FAQ
ISSUES



210713.1 Paul Robinson Fix "file 0" Improvement Open


Section 2.14, 6.2.2, 6.2.4, pg various
BACKGROUND

In DWARF v5, we changed the line-table header so that the directory and
file tables started with index 0 (not 1) and specifically required that
directory 0 match the CU's DW_AT_comp_dir, and file 0 describe the main
source file, matching the CU's DW_AT_name.  Thus, file 0 necessarily 
points to directory 0, and the combination matches DW_AT_comp_dir + 
DW_AT_name.

However, we missed making two related changes.  First, the initial state
for the "file" register of the line-table state machine remained 1, even
though it would make more sense for it to be 0; second, the description
of DW_AT_decl_file said that 0 meant "no source file."  (Note that prior
DWARF versions didn't specify any particular file number for the main
source file, and presumably we picked 1 because what else would you do.)

While it is technically possible to conform to both the line table's
requirement that file 0 mean the primary source file, and DW_AT_decl_file
not using file 0 (by duplicating an entry for the primary source file),
this is wasteful and inconsistent.

Also, non-normative text introduced in DWARF v5 suggested that file 0
had always meant the primary source file; that's actually not true.

This proposal fixes all the above problems.

SPECIFIC CHANGES

Section 2.14 Declaration Coordinates

- p.50 lines 20-21, delete the sentence starting "The value 0..."

Section 6.2.2 State Machine Registers

- p.151, in the description of the "file" register, add:

    Files are numbered beginning at 0.

Table 6.4 Line number program initial state

- change the initial value for "file" from 1 to 0

Section 6.2.4 The Line Number Program Header

- p.158, lines 4-8, edit the non-normative paragraph starting "Prior to
  DWARF Version 5, ..." so that it reads as follows.


Prior to DWARF Version 5, the current compilation file name did not have
a specific entry in the file_names field.  Starting in DWARF Version 5,
the current compilation file name has index 0.






All logos and trademarks in this site are property of their respective owner.
The comments are property of their posters, all the rest © 2007-2021 by DWARF Standards Committee.