llvm dev - Jan 2012 - [LLVMdev] Using llvm command line functions from within a plugin?

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

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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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.

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
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

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
> >
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>


-- 
-- Talin
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