[LLVMbugs] [Bug 13544] New: Passing a library multiple times to llvm-ld destroys order of positional arguments

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=13544

             Bug #: 13544
           Summary: Passing a library multiple times to llvm-ld destroys
                    order of positional arguments
           Product: tools
           Version: 3.1
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: llvm-ld
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: stefan at stefant.org
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


If a library is passed multiple times to llvm-ld without any other library in
between, then the order of the following arguments is destroyed.

This is caused by the code in llvm-ld.cpp, line 595:

  // Remove any consecutive duplicates of the same library...
  Libraries.erase(std::unique(Libraries.begin(), Libraries.end()),
                  Libraries.end());

This does not work for two reasons:

1) Consecutive duplicates in the Libraries array may not be consecutive
arguments, if there are input-file arguments in between -> requires checking of
getPosition for the possible duplicates

2) cl::list::erase only erases the argument string, but does not update the
Position vector, i.e., the arguments and the positions are out-of-sync after
erase -> erase() must be overloaded to update the Position vector too.

This causes problems in the following BuildLinkItems function call.

Example: 

llvm-ld main.bc -lm crt0.bc -lm -Lsomepath symbols.bc -lsyms

will result in the following Items list:

main.bc -lm crt0.bc -lsyms symbols.bc 

Note that 1) -lm now only appears once and 2) symbols.bc and -lsyms changed
positions, both can lead to unresolved symbols.

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