[patch] Deal with full path in .file 0 directive

[Eric Botcazou]

Hi,

after https://sourceware.org/pipermail/binutils/2021-September/117880.html, 
Gas uses the directory part, if present, of the .file 0 directive to set entry 
0 of the directory table in DWARF 5, which represents the "current directory".

Now Gas also uses the file part of the same directive to set entry 0 of the 
file table, which represents the "current compilation file".  But the latter 
need not be located in the former so GCC will use a full path in the file part 
when it is passed a full path:

gcc -c /full/path/test.c -save-temps

yields:

 .file 0 "/current/directory" "/full/path/test.c"

in the assembly file and:

 The Directory Table (offset 0x22, lines 2, columns 1):
  Entry Name
  0     (indirect line string, offset: 0x25): /current/directory
  1     (indirect line string, offset: 0x38): /full/path

 The File Name Table (offset 0x30, lines 2, columns 2):
  Entry Dir     Name
  0     0       (indirect line string, offset: 0x43): /full/path/test.c

in the object file.  Note the full path and the questionable Dir value in the 
0 entry of the file table.

The proposed change is to deal with a full path in the file part of the .file 
0 directive, so as to yield:

 The Directory Table (offset 0x22, lines 2, columns 1):
  Entry Name
  0     (indirect line string, offset: 0x25): /current/directory
  1     (indirect line string, offset: 0x38): /full/path

 The File Name Table (offset 0x30, lines 2, columns 2):
  Entry Dir     Name
  0     1       (indirect line string, offset: 0x43): test.c

in the object file instead.  Tested on x86-64/Linux, OK for the trunk?


2021-11-06  Eric Botcazou  <ebotcazou@adacore.com>

gas/
	* doc/as.texi (File): Update description of .file 0 directive.
	* dwarf2dbg.c (get_directory_table_entry): Remove obsolete comment
	and pass file0_dirname in recursive call.
	(allocate_filename_to_slot): Deal with a full path in the file name
	if the index number is 0.
	* testsuite/gas/elf/dwarf-5-file0.d: Fix pasto.
	* testsuite/gas/elf/dwarf-5-file0-2.d: Likewise.
	* testsuite/gas/elf/dwarf-5-file0-3.d: New file.
	* testsuite/gas/elf/dwarf-5-file0-3.s: Likewise.
	* testsuite/gas/elf/elf.exp: Run dwarf-5-file0-3.

-- 
Eric Botcazou
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