linux-kernel - RE: [PATCH] usercopy: use unsigned long instead of uintptr

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Message-ID: <169e9522f5494a47bd99c6febf90d931@AcuMS.aculab.com>
Date:   Fri, 17 Jun 2022 09:19:17 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Linus Torvalds' <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>
CC:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Linux-MM <linux-mm@...ck.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Uladzislau Rezki <urezki@...il.com>,
        "Kees Cook" <keescook@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joe Perches <joe@...ches.com>
Subject: RE: [PATCH] usercopy: use unsigned long instead of uintptr_t

From: Linus Torvalds
> Sent: 16 June 2022 20:19
> 
> On Thu, Jun 16, 2022 at 12:14 PM Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > In that situation, we'd probably just see "long long" being 128-bit
> > ("I32LP64LL128").
> 
> Looking around, it looks like people prefer "long long long" (or in
> the kernel, just "u128") for this, because so many have already gotten
> used to "long long" being 64-bit, and 32-bit architectures (where
> "long" is 32-bit and "long long" is 64-bit) are still relevant enough
> that people want to keep that.

Changing 'long long' to 128 bits will break things.
Much like a certain OS that is IL32P64LL64 because too much
code used 'long' to mean 32bits when int was 16 bits. 

gcc already has support for 128bit integers (on 64bit systems)
emulated using two 64bit registers (__u128 ??)

Anything wanting them probably wants them explicitly and even deciding
that uintmax_t is suddenly 128 bit will probably break things!

The only place I can imagine 'long long long' being used
is as "%llld" in printf formats.

Since 'short' and 'long' are both types and qualifiers
you can have 'long char, 'long short' and 'short long'.
These could be interesting on an I64L256 system :-)

	David

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