RFR [XS] 8041658: Use of -fdevirtualize on macroAssembler_x86.o (via -O2) with gcc 4.9.0 creates broken VM

Andrew Haley aph at redhat.com
Thu Apr 24 16:41:05 UTC 2014

On 04/24/2014 05:21 PM, Volker Simonis wrote:
> And I'm not quite sure how to fix this in HotSpot.
> I first thought I could solve this with an anonymous union like:
> union {
>   void* _relocbuf[ _relocbuf_size ];
>   Relocation _reloc;
> }
> Relocation* reloc() const { return &_reloc; }
> but unfortunately I can't put a Relocation into a union because it is
> not a POD (at least not with C++98).
> Any other ideas how we could fool GCC 4.9?
> I more and more think this should be fixed in GCC because I can
> imagine this will also break other code.

Only code that is not legal C++, and GCC developers have historically
been very reluctant to support that.  So, it might not happen.

AFAICS there is no C++98 way to embed a non-POD object in an object in this
way.  It could be done via a pointer, but that wastes some space.


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