[Reproducible-builds] Minimising work needed for this build-path issue

[Daniel Kahn Gillmor]

On Wed 2016-08-24 07:20:00 -0400, Ximin Luo wrote:
> 2. Define another variable SOURCE_ROOT to be set to the top-level
> source dir, and patch GCC to use this as the default value for
> debug-prefix-map (and the analogue for other languages / tools).
>
> This would have the same concrete behaviour as the current situation,
> but then we're defining yet another variable... but probably less
> tools will need to support this than SOURCE_DATE_EPOCH. And as with
> (1), this would not be necessary for the path-is-namespace languages.

Please see:

 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68848

in particular, this patch here:

 https://gcc.gnu.org/bugzilla/attachment.cgi?id=37005

See also the mild pushback from upstream about the env var
implementation:

Bernd Schmidt <bschmidt at redhat.com> wrote:

>>> Wouldn't it be simpler just to special-case -fdebug-prefix-map in
>>> gen_producer_string? The environment variable thing strikes me as
>>> unnecessary.

  https://gcc.gnu.org/ml/gcc-patches/2015-12/msg01280.html

I didn't have Ximin's analysis to back up the argument for the env var
case, and it seemed (and was) easier to just drop -fdebug-prefix-map
From gen_producer_string.

If you want to try to push this forward, i can follow up on that thread
and ask for reconsideration of the associated patch.

    --dkg
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