#14031: Linker paths carry substantial N*M overhead when many libaries are used -------------------------------------+------------------------------------- Reporter: nh2 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: #11587 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by nh2): There is more info from `sphalerite` on `#nixos` on the topic of dynamic linking. Apparently it ''is'' possible to give "default locations" for .so files, instead of using RPATHs: {{{ sphalerite[m]: I opened an issue about that (linking through absolute paths rather than rpath) a couple of months back https://github.com/NixOS/nixpkgs/issues/24844 it's possible, just not implemented sphalerite[m]: on linux that is -- on macOS it's already done through absolute paths nh2: that's excellent news, can you give me a short summary of what I have to do to give it an explicit path? Also, will the resulting link just be a "hint", so still be overridable with LD_LIBRARY_PATH? sphalerite[m]: It's not implemented in nixpkgs's machinery yet, so you'd need to pass absolute paths to the linker manually instead of using `-l<library>` sphalerite[m]: and no, it would not be overridable using LD_LIBRARY_PATH at that point. LD_PRELOAD would still work though. sphalerite[m]: That stuff is all discussed in the issue comments though nh2: I'm getting a bit lost in the amount of comments; what feature/flags to ld is the magic that has this effect? sphalerite[m]: passing absolute paths instead of -lXYZ sphalerite[m]: so rather than -lreadline, /nix/store/...-readline-1.2.3/lib/libreadline.so.12345 nh2: ah, so passing explicit .so to `ld` doesn't do the same as `-l` does, but instead makes it do this "default path link"? I always assumed `-l` just finds files and then passes them normally (or so at least `man ld` suggests) sphalerite[m]: Yeah no, it's not the same sphalerite[m]: Huh, actually they seem to be producing the same result for me in a test I did just now }}} [https://github.com/NixOS/nixpkgs/issues/24844 This nix issue] discusses the mentioned approach. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14031#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler