Re: [PATCH] Generate reproducible output independently of the build-path

[Ximin Luo <infinity0 at pwned dot gg>]

Ximin Luo:
> Joseph Myers:
>> On Wed, 2 Nov 2016, Ximin Luo wrote:
>>
>>> This patch series adds a new environment variable SOURCE_PREFIX_MAP. When this
>>> is set, GCC will treat this as an implicit "-fdebug-prefix-map=$value"
>>> command-line argument. This makes the final binary output reproducible, and
>>
>> Only one argument?  Sometimes you may want multiple -fdebug-prefix-map 
>> options (for both source and build directories, for example).  Perhaps the 
>> value should be split on spaces to provide multiple such mappings?
>>
> 
> We wanted to keep this environment variable simple, and allowing this would make it more costly for other projects to adopt.
> 
> Whichever separator character we choose, we would have to either (a) disallow it within the oldprefix/newprefix strings like what PATH does or (b) think of an escaping scheme. Neither choice is great - with (a) since we want to map *arbitrary* paths the restriction is less acceptable here than in PATH, and with (b) it adds complexity to the spec, for uncommon use-cases.
> 

If we picked '\n' as the separator character, we could perhaps live with the (a) restriction. I'll wait a while for others to comment some more.

> In the case of an out-of-tree build, it is still possible with the current proposal. Instead of:
> 
> SOURCE_PREFIX_MAP="srcprefix=srcname:buildprefix=buildname"
> 
> One could arrange the tree like:
> 
> commonprefix/srcname
> commonprefix/buildname
> 
> then set SOURCE_PREFIX_MAP="commonprefix=." or SOURCE_PREFIX_MAP="commonprefix/=".
> 

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