Hello,
when building TF-M you get the same result no matter what computer you build from assuming all the tooling is the same version.
The builds are reproducible in other words.
But when building TF-M together with the tests, e.g. by building the regression test suite you will get a different binary depending on where in the filesystem the tf-m-tests repository has been installed.
This is because the TEST_FAIL macro uses the gcc macro _FILE_ which injects the absolute paths of source files into strings in the binary.
This is a big problem for people using CI systems as a different sized binary can affect race conditions, flash region usage overflows, etc..
I think we should make builds reproducible by default, possibly with a configuration for adding absolute paths into the binary for those that prefer so.
I would like to write a patch to this affect, but would prefer to get some feedback now so I don't have to re-write it in review.
The simplest solution is to remove __FILE__ from the TEST_FAIL macro,but this would remove useful information and may also fail in the future if someone else uses __FILE__.
The more common way of solving this problem is to add a flag to the compiler that instructs it to replace any occurrences of the absolute path with something else during macro expansion. For instance replace "C:/repos/tf-m-tests/source_file.c" with "TFM_TESTS/source_file.c". For gcc the flag is -fmacro-prefix-map=<old_string>=<new_string>. I don't know what the flag is for the other supported compilers or if they support it at all.
Would it be OK to only support reproducible builds for the compilers that support an equivalent of macro-prefix-map?