[Bug binutils/29535] Invalid combination of debug info attributes DW_AT_name and DW_AT_comp_dir with absolute source file path

[nickc at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29535

Nick Clifton <nickc at redhat dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |nickc at redhat dot com

--- Comment #1 from Nick Clifton <nickc at redhat dot com> ---
Hi Ralf,

  [I am selectively quoting from parts of your description....]

>    <a0>   DW_AT_name        : ../test.c
>    <a4>   DW_AT_comp_dir    : /home/<user>/src/test-binutils/build

> Combining DW_AT_name, '/' and DW_AT_comp_dir returns the correct path 
> to the used source file.

But the DWARF standard does not specify that these two attributes should
be combined when using absolute paths.  In fact in section 3.1.1 it says:

  A DW_AT_name attribute whose value is a null-terminated string 
  containing the full or relative path name (relative to the value 
  of the DW_AT_comp_dir attribute, see below) of the primary source 
  file from which the compilation unit was derived.

So the DW_AT_comp_dir attribute is only used when DW_AT_name contains
a relative path, not an absolute one.


> The problem happens when using absolute paths:
> 
> gcc -C -o test.o ~/src/test-binutils/test.c -g

[Note - you are giving an absolute path to gcc, and also asking it to
generate debug information].

>     <a0>   DW_AT_name        : /home/<user>/src/test-binutils/test.c
>     <a4>   DW_AT_comp_dir    : /home/<user>/src/test-binutils/build

Which happens because this is what gcc tells the assembler to do:

  % gcc -C -o test.o ~/src/test-binutils/test.c -g -fdump-debug
  % head test.c.341t.debug
  DWARF for /home/nickc/src/test-binutils/test.c
  DIE    0: DW_TAG_compile_unit (0x1521e1c2a190)
    abbrev id: 0 offset: 0 mark: 0
    DW_AT_producer: "GNU C17 12.2.1 20220819 (Red Hat 12.2.1-1) -mtune=generic
-march=x86-64 -g"
    DW_AT_language: 29
    DW_AT_name:
"/home/nickc/work/builds/binutils/current/x86_64-pc-linux-gnu/tests/pr29535.c"
    DW_AT_comp_dir:
"/home/nickc/work/builds/binutils/current/x86_64-pc-linux-gnu/tests"

And if you check in gcc's assembler output you will find both of those 
absolute paths.

Cheers
  Nick

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