[LLVMbugs] [Bug 524] NEW: [X86] Linkonce symbols are not emitted to a link-once section

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.cs.uiuc.edu/bugs/show_bug.cgi?id=524

           Summary: [X86] Linkonce symbols are not emitted to a link-once
                    section
           Product: libraries
           Version: 1.0
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: X86 Backend
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: sabre at nondot.org


Consider the following testcase:

---
struct Foo  
    Foo();  
    virtual ~Foo();  
};  
  
struct Bar {  
    Bar();  
    virtual ~Bar();  
    virtual bool test(bool) const;  
};  
struct Baz : public Foo, public Bar  {  
    Baz();  
    virtual ~Baz();  
    virtual bool test(bool) const;  
};  
bool Baz::test(bool) const { return true;  }  
Baz::~Baz() {}
----

This has a bunch of stuff, but the important part is that it requires virtual
function thunks to be emitted.  These thunks have linkonce linkage, but the X86
backend emits them like this (for example):

        .text
        .align  16
        .globl  _ZThn4_N3BazD0Ev
        .type   _ZThn4_N3BazD0Ev, @function
_ZThn4_N3BazD0Ev:
 ...


G++, on the other hand, emits them like this:

        .set    .LTHUNK2,_ZN3BazD0Ev
        .section        .gnu.linkonce.t._ZThn4_N3BazD0Ev,"ax", at progbits
        .align 2
        .p2align 4,,15
        .weak   _ZThn4_N3BazD0Ev
        .type   _ZThn4_N3BazD0Ev, @function
_ZThn4_N3BazD0Ev:
   ...
        .size   _ZThn4_N3BazD0Ev, .-_ZThn4_N3BazD0Ev

This is causing link failures when building shared libraries with llc for QT.

-Chris



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