[LLVMdev] Problems loading passes on Mac OS X

[Chris Lattner]

On Sat, 19 Jun 2004, Michael McCracken wrote:
> I used the following short code to test loading the .dylib, and dlopen
> works fine, but dlsym is less pretty - on OS X, it automatically
> prepends an underscore to the symbol, which means that if you are
> looking for main(), you ask for "main" and it looks for "_main", which
> is how the symbols are named in Mach-O.
> This could be the source of a problem - how does GetAddressOfSymbol in
> DynamicLinker.cpp use dlsym?

I believe that GetAddressOfSymbol is only used by the JIT.  The -load
mechanism just dlopens a shared object.  Shared objects for plugins have
static constructors (".init" section) that are supposed to autoregister
the pass when the plugin is loaded.

I don't know anything about how dynamic object loading works on OS/X
(obviously), but it sounds like it's not running the static constructor.

> Does it assume anything about the symbol names?

I don't know what it will take to get the JIT working on OS/X: it might
have to autoprepend an _.  Since we don't (yet) have a PPC JIT, this isn't
an issue though.

-Chris



> On Jun 19, 2004, at 2:07 PM, Chris Lattner wrote:
>
> > On Sat, 19 Jun 2004, Michael McCracken wrote:
> >
> >> Hi, I can't get opt to list (in -help) passes that I load using -load.
> >> I see in the list archives that a similar problem has been brought up
> >> before but I didn't see whether it was resolved. Also, this is on Mac
> >> OS X, and the previous question was about Linux.
> >
> > The problem is that this has not been implemented yet on Mac OSX.  If
> > you're familiar with the OS/X interfaces for loading .so files, it
> > should
> > be pretty easy.  Take a look at lib/Support/DynamicLinker.cpp.  I think
> > that OS/X doesn't have windows.h :), and it also doesn't have dlopen.
> > If
> > you can provide the necessary magic for your platform, it should just
> > work.
> >
> > -Chris
> >
> >
> >
> >
> >> This problem happens with the Hello pass, so I'll use that to
> >> illustrate. I'm using LLVM 1.2.
> >> The plugin loads with no complaints, so dlopen() is returning success,
> >> and OS X's dlcompat probably isn't the problem.
> >> However, it never gets registered. I've included a transcript below.
> >>
> >> I also included some info about the compiler versions, etc. - It's OS
> >> X
> >> 10.3.4.
> >> Note that on OS X, 'libtool' isn't gnu libtool - that's called
> >> 'glibtool', if that matters.
> >>
> >> Does anyone have some hints on how to get this working? Thanks.
> >>
> >> transcript:
> >>
> >> % cd llvm/lib/Transforms/Hello/
> >> % make
> >> Compiling Hello.cpp
> >> Linking hello dynamic debug library
> >> ----------------------------------------------------------------------
> >> Libraries have been installed in:
> >>     /Users/mike/Documents/hpcl/LLVM/llvm/lib/Debug
> >>
> >> If you ever happen to want to link against installed libraries
> >> in a given directory, LIBDIR, you must either use libtool, and
> >> specify the full pathname of the library, or use the `-LLIBDIR'
> >> flag during linking and do at least one of the following:
> >>     - add LIBDIR to the `DYLD_LIBRARY_PATH' environment variable
> >>       during execution
> >>
> >> See any operating system documentation about shared libraries for
> >> more information, such as the ld(1) and ld.so(8) manual pages.
> >> ----------------------------------------------------------------------
> >> ======= Finished building hello dynamic debug library =======
> >> Linking hello.o
> >>
> >> % opt -load ../../Debug/libhello.dylib -hello
> >> Unknown command line argument '-hello'.  Try: 'opt --help'
> >>
> >> % g++ -v
> >> Reading specs from /usr/libexec/gcc/darwin/ppc/3.3/specs
> >> Thread model: posix
> >> gcc version 3.3 20030304 (Apple Computer, Inc. build 1495)
> >>
> >> % glibtool --version
> >> ltmain.sh (GNU libtool) 1.5 (1.1220 2003/04/05 19:32:58)
> >>
> >> _______________________________________________
> >> LLVM Developers mailing list
> >> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> >> http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev
> >>
> >
> > -Chris
> >
> > --
> > http://llvm.cs.uiuc.edu/
> > http://www.nondot.org/~sabre/Projects/
> >
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>
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-Chris

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