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3996 :: Dynamic library loading on Linux (dlopen)

• matkuki (orginal) [2018-06-29T09:12:31+02:00] view original

  Is there a way to set the flags of dlopen when Nim loads dynamic .so libraries on Linux?

  I want to add the RTLD_GLOBAL flag to it.

  Thanks

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• Araq (orginal) [2018-06-29T15:58:54+02:00] view original

  I don't think it's possible except patching lib/system/dyncalls.nim. It used to use this flag and then it got PR'ed away. Not sure why, I never understood the dlopen flags. (And I don't want to learn about it either, it's artificial complexity.)

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• matkuki (orginal) [2018-06-29T22:12:31+02:00] view original

  @Araq Excellent! I made a modification to lib/system/dyncalls.nim and it works like a charm, thanks.

  Just changed the nimLoadLibrary procedure line from:

  result = dlopen(path, RTLD_NOW)
  Run

  I will try to find the PR you mentioned. to:

  result = dlopen(path, RTLD_NOW or RTLD_GLOBAL)
  Run

  and added the RTLD_GLOBAL constant definition:

  const RTLD_GLOBAL = cint(0x0100)
  Run

  Will try to find the PR you mentioned. Strange that no-one ran into this issue before.

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• shashlick (orginal) [2018-06-29T22:29:15+02:00] view original

  Here's some context:

  2015: https://github.com/nim-lang/Nim/issues/2408 2014: https://github.com/nim-lang/Nim/pull/897

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• matkuki (orginal) [2018-06-29T23:12:31+02:00] view original

  @shashlick Thanks! Oh I see, the one PR added a global_symbols flag to the dynlib.loadLib call. That is one way of making it work, great! But that means changing all the dynamic library procedure definitions from the nice pragma syntax:

  proc myExtFunc*() {.importc: "myExtFunc", dynlib: myLibrary, cdecl.}
  Run

  to a load-to-variable way of:

  import dynlib
  var myExtlib = dynlib.loadLib("myExtlib.so", global_symbols=true)
  var myExtFunc*: proc() {.cdecl.}
  myExtFunc = cast[type(myExtFunc)](myExtlib.symAddr("myExtFunc"))
  Run

  which works but does not look as satisfyingly simple.

  The issue from 2015 that would add the global symbol functionality to the dynlib pragma is still unresolved, so I am guessing that no one made a PR for @Araq 's suggestion of loading with RTLD_GLOBAL by default and adding a -d:noRtldGlobal switch. I would basically do almost the same thing that @micklat did for the dynlib.loadLib, but with the -d:noRtldGlobal switch. Is it still an option for me adding a PR like that?

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• shashlick (orginal) [2018-06-29T23:28:38+02:00] view original

  Absolutely, I'm sure Araq will appreciate a PR that fixes that issue. Though I'm wondering if that's the right approach - it will be nicer to set that flag on a per load basis rather than globally. If you import multiple libs and only some need it and others don't, it will cause yet another issue.

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• dariolah (orginal) [2019-05-05T17:41:59+02:00] view original

  Is anyone working on this?

  One workaround is to override dlopen and force RTLD_GLOBAL flag.

  
  {. passL:"-rdynamic -Wl,-wrap,dlopen".}
  
  {.emit: """
  #include <dlfcn.h>
  #include <stdio.h>
  
  void *__real_dlopen(const char *filename, int flags);
  
  void *__wrap_dlopen(const char *filename, int flags)
  {
    printf("shadow dlopen with RTLD_GLOBAL: %s\n", filename);
    fflush(stdout);
    return __real_dlopen(filename, RTLD_NOW | RTLD_GLOBAL);
  }
  """.}
  Run

  IUP fontDlg works now.

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