linux-kernel - Re: [PATCH] alpha/elf: Fix misc/setarch test of util-linux by removing 32bit support

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Message-Id: <6c1f31be-cd3b-4090-abbd-fd3968858e1b@app.fastmail.com>
Date: Sat, 11 Jan 2025 12:26:18 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Eric W. Biederman" <ebiederm@...ssion.com>,
 "John Paul Adrian Glaubitz" <glaubitz@...sik.fu-berlin.de>
Cc: "Richard Henderson" <richard.henderson@...aro.org>,
 "Matt Turner" <mattst88@...il.com>, "Kees Cook" <kees@...nel.org>,
 "Paul E. McKenney" <paulmck@...nel.org>, linux-alpha@...r.kernel.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 "Michael Cree" <mcree@...on.net.nz>, "Sam James" <sam@...too.org>,
 "Maciej W. Rozycki" <macro@...am.me.uk>,
 "Geert Uytterhoeven" <geert@...ux-m68k.org>,
 "Michael Karcher" <kernel@...rcher.dialup.fu-berlin.de>,
 "Chris Hofstaedtler" <zeha@...ian.org>, util-linux@...r.kernel.org,
 linux-mips@...r.kernel.org, loongarch@...ts.linux.dev
Subject: Re: [PATCH] alpha/elf: Fix misc/setarch test of util-linux by removing 32bit
 support

On Sat, Jan 11, 2025, at 01:16, Eric W. Biederman wrote:
> Richard Henderson <richard.henderson@...aro.org> writes[1]:
>
>> There was a Spec benchmark (I forget which) which was memory bound and ran
>> twice as fast with 32-bit pointers.
>>
>> I copied the idea from DEC to the ELF abi, but never did all the other work
>> to allow the toolchain to take advantage.
>>
>> Amusingly, a later Spec changed the benchmark data sets to not fit into a
>> 32-bit address space, specifically because of this.
>>
>> I expect one could delete the ELF bit and personality and no one would
>> notice. Not even the 10 remaining Alpha users.
>
> In [2] it was pointed out that parts of setarch weren't working
> properly on alpha because it has it's own SET_PERSONALITY
> implementation.  In the discussion that followed Richard Henderson
> pointed out that the 32bit pointer support for alpha was never
> completed.
>
> Fix this by removing alpha's 32bit pointer support.
>
> As a bit of paranoia refuse to execute any alpha binaries that hafe
> the EF_ALPHA_32BIT flag set.  Just to fail explicitly in case someone
> somewhere has binaries that trying to use alpha's 32bit pointer
> support.
>
> [1] 
> https://lkml.kernel.org/r/CAFXwXrkgu=4Qn-v1PjnOR4SG0oUb9LSa0g6QXpBq4ttm52pJOQ@mail.gmail.com
> [2] 
> https://lkml.kernel.org/r/20250103140148.370368-1-glaubitz@physik.fu-berlin.de
> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>

Reviewed-by: Arnd Bergmann <arnd@...db.de>