[PATCH] [lld] [MachO] Begin to flesh out normalizedToAtoms

[Chandler Carruth]

On Thu, Jan 2, 2014 at 8:07 PM, Nick Kledzik <kledzik at apple.com> wrote:

> On Jan 2, 2014, at 4:41 PM, Joey Gouly <joey.gouly at gmail.com> wrote:\
> >
> >
> > ================
> > Comment at: lib/ReaderWriter/MachO/MachONormalizedFileYAML.cpp:282
> > @@ -280,1 +281,3 @@
> > +        io, sect.content);
> > +    io.mapOptional("content",         content->normalizedContent);
> >     io.mapOptional("relocations",     sect.relocations);
> > ----------------
> > kledzik at apple.com wrote:
> >> I think you can just cast the address of sect.content to be of type
> ContentBytes and it should all just work with no need for NormalizedContent.
> > mapOptional wants a reference to the content, so I cant use the address
> of content, and as far as I can tell, I can't change the type of a
> reference.
> >
> > Unless I'm mistaken, I can't do this without copying.
>
> This works for me:
>
> Index: lib/ReaderWriter/MachO/MachONormalizedFileYAML.cpp
> ===================================================================
> --- lib/ReaderWriter/MachO/MachONormalizedFileYAML.cpp  (revision 198349)
> +++ lib/ReaderWriter/MachO/MachONormalizedFileYAML.cpp  (working copy)
> @@ -276,7 +276,8 @@
>      io.mapOptional("attributes",      sect.attributes);
>      io.mapOptional("alignment",       sect.alignment, 0U);
>      io.mapRequired("address",         sect.address);
> -    io.mapOptional("content",         sect.content);
> +    ContentBytes &cont = *reinterpret_cast<ContentBytes*>(&sect.content);
>

Using the vector after this is totally undefined behavior. You can't just
cast vector<T>* to vector<U>* and then access the vector with that pointer
when T != U. It doesn't matter what the layout or size of T and U are, the
vector types are completely different and might have nothing to do with
each other.
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