[LLVMbugs] [Bug 1318] NEW: Options in loadable modules are not available

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=1318

           Summary: Options in loadable modules are not available
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Support Libraries
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: rspencer at x10sys.com


This is related to bug 1317.

When a loadable module is loaded its command line options are not available
until the loaded module has been processed. This is a bit of a chicken-and-egg
problem:

1. Option values aren't available until after ParseCommandLineOptions
2. A -load option doesn't get processed until after ParseCommandLineOptions
3. Options in the loaded module can't been seen by ParseCommandLineOptions
4. Unrecognized option errors are generated by ParseCommandLineOptions because
   the module hasn't been loaded yet.

Consequently, you get errors about the names of optimization passes. I'm not
sure how this ever worked or if its a result of the recent changes to CommandLine.

There are several things we could do to rectify this:

1. Make a formal API for "foreign passes". That is, when we dlopen the shared
   object we look for a function of a particular name, add its address to a
   table of foreign passes, invoke that function to initialize, etc. This 
   API could do many other things (like build a PassManager full of passes).

2. Incorporate the --load option into CommandLine. It would become a new type
   of option that contains a list of function addresses. The functions are 
   obtained by dlopen/dlsym on the shared object. The function (in the 
   shared object) is invoked to *properly* register any command line options. 
   This implies that static option objects are not permitted in such objects.

3. We might want to add something to Support library that could be used (but
   not linked into) the loadable module. This would be an interface to make
   "LLVM compatible loadable modules" that takes care of many of the details.
   I.e. it provides a cleaner client side interface for the module writer. 
   This lib would be linked into all tools that support --load.



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