Some tools will record the path of the source files in their output.
Most compilers write the path of the source in the debug information in order to locate the associated source files.
Some tools have flags (like gzip’s
-n) that prevent them from writing
the path in their output. Proposing patches to add a similar feature in
other tools might be sufficiently easy.
In most cases however, post-processing is required to either remove the build path or to normalize it to a predefined value.
For the specific case of debug
symbols, there is currently no good
post-processing tool to
change them to a pre-determined value1. A work-around is to
define the build path as part of the build environment,
reprotest changes it so this makes it harder to assess reproducibility.
Certain compiler flags can work around the issue:
-fdebug-prefix-map=OLD=NEWcan strip directory prefixes from debug info. (available in all GCC versions, Clang 3.8)
-fmacro-prefix-map=OLD=NEWis similar to
-fdebug-prefix-map, but addresses irreproducibility due to the use of
__FILE__macros and alike. (available since GCC 8, Clang support is pending)
-ffile-prefix-map=OLD=NEWis an alias for both
-fmacro-prefix-map. (available since GCC 8, Clang support is pending)
Note that some packages save the compile options in the build output.
This is also problematic because this will also apply to intermediate source files that other tools generate. As they typically will use random file names, having a fixed build path is not enough in such cases.
A build-path-prefix-map specification is in discussion with the GCC developers.