[llvm-dev] [lld] RFC: Finding shared libraries on OpenBSD

[Rui Ueyama via llvm-dev]

Hi Mark,

If we have to do this, or LLD doesn't work on OpenBSD, I think we need to
do this. But can I ask one question? I wonder why OpenBSD systems don't
have symbolic links unlike the other Unix-like systems in the first place.

On Mon, Dec 19, 2016 at 2:27 PM, Mark Kettenis via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> On OpenBSD we still use the "classic" SunOS 4 shared library
> versioning scheme where the major and minor number are part of the
> library name (and recorded in DT_NEEDED entries).  For example the
> shared libc on the OpenBSD-current is named libc.so.89.2.  With this
> scheme, linker has to pick the pick the library with the highest major
> and minor (within the highest major version); the symbolic links
> present on most other ELF-based systems don't exist on OpenBSD.  The
> diff below implements this search algorithm.  It follows the same
> approach of iterating over files in a directory as the implementation
> in the native (ld.bfd derived) toolchain.
>
> This is an RFC as I'm not sure the diff is the best way to implement
> this.  For one thing, iterating over files is probably undesirable on
> non-OpenBSD systems.  And the searching code should probably be moved
> to its own function.
>
>
> Index: ELF/DriverUtils.cpp
> ===================================================================
> --- ELF/DriverUtils.cpp (revision 290066)
> +++ ELF/DriverUtils.cpp (working copy)
> @@ -153,9 +153,34 @@
>      return findFromSearchPaths(Name.substr(1));
>
>    for (StringRef Dir : Config->SearchPaths) {
> -    if (!Config->Static)
> +    if (!Config->Static) {
>        if (Optional<std::string> S = findFile(Dir, "lib" + Name + ".so"))
>          return S;
> +
> +      const StringRef LibName = (Twine("lib") + Name + ".so.").str();
> +      int MaxMaj = -1, MaxMin = -1;
> +      std::error_code EC;
> +      for (fs::directory_iterator LI(Dir, EC), LE;
> +          !EC && LI != LE; LI = LI.increment(EC)) {
> +        StringRef FilePath = LI->path();
> +       StringRef FileName = path::filename(FilePath);
> +       if (!(FileName.startswith(LibName)))
> +         continue;
> +       std::pair<StringRef, StringRef> MajMin =
> +         FileName.substr(LibName.size()).split('.');
> +       int Maj, Min;
> +       if (MajMin.first.getAsInteger(10, Maj) || Maj < 0)
> +         continue;
> +       if (MajMin.second.getAsInteger(10, Min) || Min < 0)
> +         continue;
> +       if (Maj > MaxMaj)
> +         MaxMaj = Maj, MaxMin = Min;
> +       if (MaxMaj == Maj && Min > MaxMin)
> +         MaxMin = Min;
> +      }
> +      if (MaxMaj >= 0)
> +       return findFile(Dir, LibName + Twine(MaxMaj) + "." +
> Twine(MaxMin));
> +    }
>      if (Optional<std::string> S = findFile(Dir, "lib" + Name + ".a"))
>        return S;
>    }
>
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