[Webkit-unassigned] [Bug 214142] [WTF] Fix PackedAlignedPtr for X86_64 canonical addresses

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=214142

--- Comment #5 from Mark Lam <mark.lam at apple.com> ---
(In reply to Jim Mason from comment #3)
> (In reply to Mark Lam from comment #2)
> > Jim, what platform actually allocates user space memory in the range where
> > bit 47 of the address is set?  Can you share the detail?
> 
> Solaris/illumos.  See https://www.oracle.com/solaris/technologies/memory.html
> 
> I first thought this was a Solaris quirk, and for a long time, just
> self-applied the attached patch to make it work in my environment.  When I
> learned that X86_64 actually specifies the canonical address space, such
> that the 'hole' of unusable addresses is in the middle of the virtual space,
> I reckoned it would be worthwhile to share the fix, so that webkit always
> does the right thing for this processor architecture.

According to https://www.oracle.com/solaris/technologies/memory.html, addresses with bit 47 set are all reserved for Kernel space.  In fact, the upper bound in user space memory is 0x00008000.00000000 i.e. you should never see an address with bit 47 set in WebKit.  Am I missing something?

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