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 <bschm...@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.
> 

Thanks, I did see this a while ago and forgot about it. However it does differ 
from the current proposal in an important way.

Current proposal (2): GCC should, if SOURCE_ROOT is set and debug-prefix-map is 
not given, *automatically* use this variable. There is no opportunity for the 
user to tell GCC to look at a different variable.

OTOH your patch above has GCC read a user-supplied variable. I think we want to 
avoid this, for the same reason that we pushed quite heavily for upstreams to 
support SOURCE_DATE_EPOCH and not their own custom command line option. It 
would also fix packages using gcc but not dpkg-buildflags (and for other 
distros, etc).

But for sure we can start from the code that you already wrote. :)

X

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