linux-kernel - Re: [PATCH] alpha: Fix personality flag propagation across an exec

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Message-ID: <alpine.DEB.2.21.2501091953050.18889@angie.orcam.me.uk>
Date: Thu, 9 Jan 2025 20:10:39 +0000 (GMT)
From: "Maciej W. Rozycki" <macro@...am.me.uk>
To: "Eric W. Biederman" <ebiederm@...ssion.com>
cc: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>, 
    Arnd Bergmann <arnd@...db.de>, 
    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>, 
    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: Fix personality flag propagation across an exec

On Thu, 9 Jan 2025, Eric W. Biederman wrote:

> > So, this would be the 100% correct for alpha then which would not loose
> > any functionality even for 32-bit binaries?
> 
> I don't think it is correct to think about 32-bit binaries on alpha.
> 
> Alpha never had a 32bit instruction set.  But at some point it looks
> like binaries that could not handle more than 31 bits of address
> space got ported and someone implemented a work-around.  I guess this
> is the --taso option that Arnd mentioned.

 This also saves some code space in non-PIE and plain static executables 
as it takes fewer machine instructions to load a 64-bit address that is 
known beforehand to be a sign-extended 32-bit value.

 This is similar to the MIPS n32 ABI, which also implies a 32-bit address 
space while still using 64-bit registers for everything, starting from 
stack slots (it's also ILP32 with the `long long' C data type only making 
proper use of the full width of the CPU registers, while Alpha's --taso 
ABI is I believe IP32 (?) with the plain `long' C data type still 64-bit, 
just as with the regular LP64 ABI).

 This saving turned out quite important for some MIPS applications; less 
so for the Alpha, where indeed it was mainly a portability matter at the 
time when going beyond 32 bits (and writing clean code in the first place) 
was a big thing for some people.

  Maciej