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Date: Mon, 03 Mar 2008 14:55:30 -0800
From: "H. Peter Anvin" <hpa@...or.com>
To: Segher Boessenkool <segher@...nel.crashing.org>
CC: hans.rosenfeld@....com, torvalds@...ux-foundation.org,
linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
Arjan van de Ven <arjan@...ux.intel.com>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: bisected boot regression post 2.6.25-rc3.. please revert
Segher Boessenkool wrote:
>>> so (on 32-bit) ~_PAGE_PSE is ~0x80L is 0xffffff7f, which when cast to
>>> 64-bit is 0x00000000ffffff7f,
>>
>> Actually, it is signed, so this isn't true. Comments about unsafeness
>> still apply.
>
> It turns out that PAGE_SIZE is unsigned. So this gives us for
>
> (~PAGE_MASK & ~_PAGE_USER & ~_PAGE_PSE & ~_PAGE_NX)
>
> the types UL, L, L, ULL resp.
>
> The associativity of & is left-to-right, so this in turn becomes
>
> UL, L, ULL
>
> UL, ULL
>
> ULL
>
> and that cast from UL to ULL doesn't sign-extend.
>
All the masks either need to be the proper size or signed.
-hpa
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