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4029 :: Trouble using dynamic libraries in Nim

• PMunch (orginal) [2018-07-09T09:56:36+02:00] view original

  I'm writing an application which I hope to split into dynamic modules so the user could switch between different implementations of parts of the system, or extend functionality. But I'm having some trouble, the GC really doesn't appear to like being called from dynamic libraries. I've got this loader:

  import dynlib
  import os
  
  type
    setupProc = proc() {.nimcall.}
  
  var
    dll: LibHandle
    setup: setupProc
  echo "Trying to load libraries from " & $(getAppDir() / "dynlibs")
  for library in walkFiles(getAppDir() / "dynlibs/*"):
    dll = loadLib(library, true)
    if dll != nil:
      echo "Loaded library " & library
      
      let setupAddr = dll.symAddr("setup")
      echo "Found setup"
      if setupAddr != nil:
        setup = cast[setupProc](setupAddr)
      if setup != nil:
        setup()
      else:
        echo "Wasn't able to load setup() from " & library
    else:
      echo "Unable to load lib from " & library
  Run

  This basically just tries to load every dynamic library in the dynlibs folder.

  Next I have my two plugins:

  # lib1.nim
  proc setup() {.exportc, cdecl.} =
    echo "Hello from plugin 1"
  Run

  proc setup() {.exportc, cdecl.} =
    echo "Hello"
    var test = @["This", "is", "the", "second", "library"]
    echo test[0]
  Run

  And of course to compile I've used these commands:

  
  $ nim c --nimcache:nimcache_libnimrtl -o:./libnimrtl.so ~/.choosenim/toolchains/nim-0.18.0/lib/nimrtl.nim
  $ nim c -d:useNimRtl loader.nim
  $ nim c --app:lib -d:useNimRtl -o:dynlibs/liblib2.so lib2.nim
  $ nim c --app:lib -d:useNimRtl -o:dynlibs/liblib1.so lib1.nim
  Run

  However when I run it I only get:

  
   $ LD_LIBRARY_PATH=`realpath ./` ./loader
  Trying to load libraries from /home/peter/div/pimo/libloaderror/dynlibs
  Loaded library with /home/peter/div/pimo/libloaderror/dynlibs/liblib1.so:
  
  Found setup with:
  
  Hello from plugin 1
  Loaded library with /home/peter/div/pimo/libloaderror/dynlibs/liblib2.so:
  
  Found setup with:
  
  Hello
  Traceback (most recent call last)
  loader.nim(23)           loader
  lib2.nim(4)              setup
  SIGSEGV: Illegal storage access. (Attempt to read from nil?)
  Run

  Deleting plugin liblib1.so the thing seems to work:

  
  $ rm dynlibs/liblib1.so
  $ LD_LIBRARY_PATH=`realpath ./` ./loader
  Trying to load libraries from /home/peter/div/pimo/libloaderror/dynlibs
  Loaded library with /home/peter/div/pimo/libloaderror/dynlibs/liblib2.so:
  
  Found setup with:
  
  Hello
  This
  Run

  Changing their load order also works:

  
  $ mv dynlibs/liblib2.so dynlibs/liblib0.so
  $ LD_LIBRARY_PATH=`realpath ./` ./loader
  Trying to load libraries from /home/peter/div/pimo/libloaderror/dynlibs
  Loaded library with /home/peter/div/pimo/libloaderror/dynlibs/liblib0.so:
  
  Found setup with:
  
  Hello
  This
  Loaded library with /home/peter/div/pimo/libloaderror/dynlibs/liblib1.so:
  
  Found setup with:
  
  Hello from plugin 1
  Run

  I've also seen errors like this which appears to show a bit more of what is actually causing the error out:

  
  $ LD_LIBRARY_PATH=`realpath ./` ./loader
  Trying to load libraries from /tmp/libloaderror/dynlibs
  Loaded library with /tmp/libloaderror/dynlibs/liblib2.so:
  
  Found setup with:
  
  Hello
  Traceback (most recent call last)
  loader.nim(23)           loader
  lib2.nim(3)              setup
  assign.nim(155)          genericSeqAssign
  assign.nim(118)          genericAssign
  assign.nim(73)           genericAssignAux
  gc.nim(289)              unsureAsgnRef
  gc.nim(218)              decRef
  SIGSEGV: Illegal storage access. (Attempt to read from nil?)
  Run

  All in all the behaviour of Nim when loading dynamic libraries seems to be a bit iffy at best. I think this issue might be related: https://github.com/nim-lang/Nim/issues/6886

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