[Webkit-unassigned] [Bug 61137] [BSD] OSAllocator::reserveUncommitted eagerly commits memory on BSD?

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=61137


Matthew Dempsky <mdempsky at google.com> changed:

           What    |Removed                     |Added
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                 CC|                            |mdempsky at google.com




--- Comment #9 from Matthew Dempsky <mdempsky at google.com>  2012-09-18 14:43:48 PST ---
> The on-demand allocator may allocate memory anywhere in the VM space, and this is a problem for x86-64, since relative branches have a range of +/- 2Gb.  If the on-demand allocator were to allocate two blocks of memory for use by the JIT more than 2Gb apart, linking could fail.

So on OpenBSD, for this reason we actually guarantee that if you use a hinted mmap(), the returned address will be within +/-2GB of the address.  E.g., if p != NULL, then mmap(p, ...) will return an address between p - 2GB and p + 2GB.

Would it be possible to modify the on-demand allocator to take advantage of this property on OpenBSD, and to use it on OpenBSD/x86-64 instead of the fixed allocator?

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