Bug#902100: webkit2gtk: Please update patch fix-ftbfs-m68k.patch

[Geert Uytterhoeven]

Hi Adrian,

On Fri, Jun 22, 2018 at 1:00 PM John Paul Adrian Glaubitz
<glaubitz at physik.fu-berlin.de> wrote:
> On 06/22/2018 12:54 PM, Geert Uytterhoeven wrote:
> >>> If anything relies on having a hole in between the two fields, explicit
> >>> padding should be added.
> >>
> >> Well, I don't think we can add this change as this reduces the size of
> >> the bitfield. Do you think we can just cut it in half without any issues?
> >
> > CSSProperty contains:
> >
> >     StylePropertyMetadata m_metadata;
> >     RefPtr<CSSValue> m_value;
> >
> > StylePropertyMetadata contains:
> >     uint16_t m_propertyID : 10;
> >     uint16_t m_isSetFromShorthand : 1;
> >     uint16_t m_indexInShorthandsVector : 2; // If this property was
> > set as part of an ambiguous shorthand, gives the index in the
> > shorthands vector.
> >     uint16_t m_important : 1;
> >     uint16_t m_implicit : 1; // Whether or not the property was set
> > implicitly as the result of a shorthand.
> >     uint16_t m_inherited : 1;
> >     uint16_t pad;
> >
> > So the bitfield is in the first uint16_t, not in a uint32_t (yes, that matters
> > on big endian).
>
> But our problem is not endianess-related, is it? Our problem is that the
> default alignment on m68k is 16 bits.

Yes, that's what the "<=" checks are for.

> > Oops, I did miss StylePropertyMetadata already has padding.
> > So the sizes of CSSProperty and SameSizeAsCSSProperty should already match.

But the "==" check should be fine, at least for the first structure, as someone
has already made the padding explicit (which is IMHO a better solution than
changing "==" to "<=").

> > To avoid future endianness issues, you still may want to reflect this in
> > SameSizeAsCSSProperty:
> >
> > --- webkitgtk-2.20.3/Source/WebCore/css/CSSProperty.cpp.orig
> > 2018-06-22 10:40:49.389060321 +0200
> > +++ webkitgtk-2.20.3/Source/WebCore/css/CSSProperty.cpp 2018-06-22
> > 12:50:51.005024268 +0200
> > @@ -29,7 +29,8 @@
> >  namespace WebCore {
> >
> >  struct SameSizeAsCSSProperty {
> > -    uint32_t bitfields;
> > +    uint16_t bitfields;
> > +    uint16_t pad;
> >      void* value;
> >  };
>
> I'm confused. The endinaness is not our problem at the moment, is it?

Not at the moment. But it may bite us in the future.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds