On Wed, 12 Aug 2020 at 01:02, Paul Smith <p...@mad-scientist.net> wrote: > > This is a kind of esoteric problem, but all the more annoying for that. > > As usual I've built my own version of GCC, and then I check it into Git > so that all builds can use this one canonical compiler regardless of > operating system, etc. > > After being checked into Git, the compiler started failing to link with > an error that it could not find libgcc_s.so, even though it exists in > exactly the same place (relatively) as it was before. > > After some debugging and strace-ing, I discovered that in the failure > mode the front-end didn't provide this flag to collect2, which is where > libgcc_s.so lives: > > -L/.../cc/unknown/bin/../lib/gcc/x86_64-unknown-linux-gnu/10.2.0/../../../../x86_64-unknown-linux-gnu/lib/../lib64/. > > The problem is this: when I built this compiler I only built the 64bit > version of it, not the 32bit version. As a result, the lib/. > directories are empty: only the lib64 directories have any content. > > When I check this into Git, of course all empty directories are > ignored. So while the /.../cc/unknown/x86_64-unknown-linux-gnu/lib64 > directory, where 64bit libgcc_s.so lives, does exist, the > /.../cc/unknown/x86_64-unknown-linux-gnu/lib directory doesn't exist, > which means the above path cannot be resolved. > > Of course, I can force the lib directory to exist by adding a dummy > file there and I will do so. However, it seems to me that it would be > better if GCC would apply a simplifying function to pathnames to reduce > all the "/.." elements, before it starts looking for directories, to > avoid failing if some unnecessary element doesn't exist. This > shouldn't be too difficult since the path will be either the same > length as, or shorter than, the original so there's no need to > reallocate memory etc.: it can be updated in place. > > Oddly, I looked through the gnulib library and didn't find any > appropriate module for this. It seems like there should be one.
C++17 provides std::filesystem::weakly_canonical for that. It doesn't help GCC or gnulib though. POSIX realpath and GNU canonicalize_file_name do the canonicalization, but require every path component to exist. I think it's worth adding this to bugzilla. Depending on the existence of empty directories seems less than ideal.
