[LLVMdev] Using llvm command line functions from within a plugin?

[Talin]

On Tue, Jan 3, 2012 at 12:42 AM, Duncan Sands <baldrick at free.fr> wrote:

> Hi Talin,
>
> > After a several-month hiatus, I've returned to working on my main LLVM
> project.
> > However, after checking out the latest LLVM head I'm encountering a new
> problem.
> > When I attempt to load my custom plugin pass into opt, I'm getting this
> error
> > message:
> >
> > dyld: lazy symbol binding failed: Symbol not found:
> > __ZN4llvm2cl3optIbLb0ENS0_6parserIbEEE4doneEv
> >    Referenced from:
> /Users/talin/Projects/tart/build-eclipse/linker/libgc.dylib
> >    Expected in: flat namespace
>
> are you sure you built opt and your plugin using the same LLVM build?  You
> can
> get this kind of thing if (eg) opt is from a Release build, but your
> plugin was
> built against a Debug build.
>
> Ah, that would explain it. You see, I normally link against the debug
version of LLVM, but because opt, llc, and clang are quite slow in debug
builds I generally copy just those three programs over to the install dir's
'bin' directory. This cuts my overall project build time by about 2/3. I
didn't realize that would be a problem.


> Ciao, Duncan.
>
> > It appears to be due to the fact that I'm using LLVM's command-line
> functions
> > from within my plugin:
> >
> >     cl::opt<bool> optShowGC("show-gc", cl::desc("Print debugging output
> from GC
> >     strategy"));
> >
> > (when I remove the option from the source, everything works fine.)
> >
> > Now, I recognize the 'flat namespace' phrase from my build file, which
> passes
> > "-Wl -flat_namespace -Wl -undefined -Wl suppress" to the linker when
> building
> > the plugin. I remember that someone gave me this magic formula (or
> perhaps I got
> > it off a search result) - I certainly don't understand what it means. I
> remember
> > it had to do with creating the plugin in such a way as to resolve
> undefined
> > symbols against the main program when loaded, instead of giving an error
> for
> > each undefined symbol. (This appears to be specific to OS X, the linker
> on Linux
> > doesn't require these flags.)
> >
> > A more general question is this - I've never really found a good
> reference or
> > tutorial for building plugin libraries, in particular the kinds used
> with LLVM.
> > I don't expect LLVM's docs to teach me how to compile and link a shared
> library,
> > but it seems like there's a fair amount of non-obvious esoterica
> involved here,
> > and it would be nice to have a pointer to some doc that would make it
> all less
> > mysterious :)
> >
> > --
> > -- Talin
> >
> >
> > _______________________________________________
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> > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
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>
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-- 
-- Talin
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