linux-kernel - Re: [PATCH 0/5] powerpc: Implement masked user access

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Message-ID: <20250624131714.GG17294@gate.crashing.org>
Date: Tue, 24 Jun 2025 08:17:14 -0500
From: Segher Boessenkool <segher@...nel.crashing.org>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: David Laight <david.laight.linux@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>, Naveen N Rao <naveen@...nel.org>,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
        Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Darren Hart <dvhart@...radead.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Andre Almeida <andrealmeid@...lia.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 0/5] powerpc: Implement masked user access

On Tue, Jun 24, 2025 at 07:27:47AM +0200, Christophe Leroy wrote:
> Ah ok, I overlooked that, I didn't know the cmove instruction, seem 
> similar to the isel instruction on powerpc e500.

cmove does a move (register or memory) when some condition is true.
isel (which is base PowerPC, not something "e500" only) is a
computational instruction, it copies one of two registers to a third,
which of the two is decided by any bit in the condition register.

But sure, seen from very far off both isel and cmove can be used to
implemente the ternary operator ("?:"), are similar in that way :-)


Segher