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

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Message-Id: <bff9bd35-4d47-45fc-90c5-28b79425fc8b@app.fastmail.com>
Date: Thu, 09 Jan 2025 21:53:51 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Maciej W. Rozycki" <macro@...am.me.uk>,
 "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: "John Paul Adrian Glaubitz" <glaubitz@...sik.fu-berlin.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, Jan 9, 2025, at 21:10, Maciej W. Rozycki wrote:
> 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).

I'm pretty sure it's still LP64 on Alpha Linux with gcc. There is an
-mpointer-size=32 option in gcc for VMS, but I don't see anything like
that in Linux. The only thing that is implemented here is the option
for the linker that sets the EF_ALPHA_32BIT bit, but none of the
code generation takes advantage of the upper bits being zero.

       Arnd