[Bug ld/13244] New: GNU LD incorrectly complain about undefined hidden symbols with LTO

[hubicka at gcc dot gnu.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=13244

             Bug #: 13244
           Summary: GNU LD incorrectly complain about undefined hidden
                    symbols with LTO
           Product: binutils
           Version: 2.23 (HEAD)
            Status: NEW
          Severity: normal
          Priority: P2
         Component: ld
        AssignedTo: address@hidden
        ReportedBy: address@hidden
    Classification: Unclassified


Created attachment 5957
  --> http://sourceware.org/bugzilla/attachment.cgi?id=5957
Mozilla source file that produces the UNDEF load.

Mozilla does not link with GNU LD with the following error:

/abuild/jh/trunk-install/lib/gcc/x86_64-unknown-linux-gnu/4.7.0/../../../../x86_64-unknown-linux-gnu/bin/ld:
 
libxul.so: hidden symbol `_mm_load_si128' isn't defined                         
/abuild/jh/trunk-install/lib/gcc/x86_64-unknown-linux-gnu/4.7.0/../../../../x86_64-unknown-linux-gnu/bin/ld:
 
final link failed: Bad value                                                    

What happens is approximately the following:

1) _mm_load_si128 is extern inline function that is assumed to be always
inlined and thus it has no non-extern inline definition in the whole DSO.  It
is also always inline, so it is OK.
2) GCC delays removal of extern inlines and virtual functions from callgraph
until after IPA inlining. This is in order to increase chances that they will
be inlined when their call is discovered later via devirtualization or when
address is taken
3) Symbol streaming outputs the symbols based at calgraph. Even though the
function was fully inlined, the kept external body makes it to output use of
_mm_load_si128 symbol
4) In resolution table we get:
974 314cd963 UNDEF _mm_load_si128  
but the refrence to _mm_load_si28 is optimized out at linktime.

The linker ought to not complain about the hidden symbol reference that has
been optimized out. At least gold behaves this way.

I am going to fix 3) at GCC side, but se still ought not to complain at 4).

Honza

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