[Webkit-unassigned] [Bug 176669] [JSC] Fold gigacage address into 32bit

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Sun Sep 10 12:33:22 PDT 2017


--- Comment #1 from Filip Pizlo <fpizlo at apple.com> ---
(In reply to Yusuke Suzuki from comment #0)
> We access caged area by doing `base + (target & mask)`.
> At that time, target is 64bit pointer.
> This is rough idea: If we can discard alignment part we can make this target
> address within 32bit.
> If the memory area is 8byte aligned, our 32bit offset can represent 32GB (4
> * 8), which matches to the current gigacage area.
> Computation becomes like, `base + (target << alignment)`.

Caging relies on the fact that it’s an identity operation for valid pointers. This breaks that property. I suggest not doing this.

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