setting -fdebug-prefix-map via envvar

[Vagrant Cascadian]

On 2020-06-26, Bill Allombert wrote:
> Is it possible to set -fdebug-prefix-map via an environment variable or
> a similar mechanism rather than through the command line ?
>
> The issue is that adding -fdebug-prefix-map=PREFIX to CFLAGS
> leads to PREFIX leaking in buildlogs and in generated Makefiles and 
> similar files that can end up inside packages, making previously
> reproducible packages unreproducible.

We had proposed BUILD_PATH_PREFIX_MAP to address exactly these kinds of
issues:

  https://reproducible-builds.org/specs/build-path-prefix-map/

Unfortunately it was not accepted into upstream GCC as they did not like
accepting input from an environment variable (yes, they let
SOURCE_DATE_EPOCH slip though!) ... not sure if many or any other
compilers have adopted it.

It would be good to revisit at some point if there is any way we could
conceivably get GCC developers on board with some variant of the
proposal. Maybe try getting into other toolchains first?


My best thought was --build-path-from-env=BUILD_PATH_PREFIX_MAP to at
least make it explicity as to which environment variable was affecting
behavior, without embedding the value of the environment variable in the
commandline... but I didn't get positive feedback on this approach back
when I presented at GNU Tools Cauldron last year and floated the idea.


live well,
  vagrant
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