[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 #6 from Jim Mason <jmason at ibinx.com> ---
(In reply to Mark Lam from comment #5)
> 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?

I think you may be looking at SPARC.  X86_64 has the user stack and shared objects up there.  It's about half way down:

      64-bit Kernel's Virtual Memory Layout. (assuming 64 bit app)

 0xFFFFFD80.00000000  |-----------------------|- KERNELBASE (lower if > 1TB)
                      |     User stack        |- User space memory
                      |                       |
                      | shared objects, etc   |       (grows downwards)
                      :                       :
                      |                       |
 0xFFFF8000.00000000  |-----------------------|
                      |                       |
                      | VA Hole / unused      |
                      |                       |
 0x00008000.00000000  |-----------------------|
                      |                       |
                      |                       |
                      :                       :
                      |       user heap       |       (grows upwards)
                      |                       |
                      |       user data       |
                      |-----------------------|
                      |       user text       |
 0x00000000.04000000  |-----------------------|
                      |       invalid         |
 0x00000000.00000000  +-----------------------+


I can confirm on Solaris that I see addresses with bit 47 both set and not set in PackedAlignedPtr, and if I don't sign-extend the ones with bit 47 set, it will SIGSEGV.

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