linux-kernel - Re: [PATCH 1/4] riscv: entry: Convert ret_from

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <alpine.DEB.2.21.2501272017140.56843@angie.orcam.me.uk>
Date: Mon, 27 Jan 2025 20:20:56 +0000 (GMT)
From: "Maciej W. Rozycki" <macro@...am.me.uk>
To: Charlie Jenkins <charlie@...osinc.com>
cc: Paul Walmsley <paul.walmsley@...ive.com>, 
    Palmer Dabbelt <palmer@...belt.com>, Huacai Chen <chenhuacai@...nel.org>, 
    WANG Xuerui <kernel@...0n.name>, Thomas Gleixner <tglx@...utronix.de>, 
    Peter Zijlstra <peterz@...radead.org>, Andy Lutomirski <luto@...nel.org>, 
    Alexandre Ghiti <alexghiti@...osinc.com>, linux-riscv@...ts.infradead.org, 
    linux-kernel@...r.kernel.org, loongarch@...ts.linux.dev
Subject: Re: [PATCH 1/4] riscv: entry: Convert ret_from_fork() to C

On Sun, 26 Jan 2025, Charlie Jenkins wrote:

> >  Wouldn't it make sense to save a jump here and make it a tail call, i.e.:
> > 
> > 	la ra, ret_from_exception
> > 	tail ret_from_fork
> > 
> 
> I don't believe so due to the return address stack. It was shown in this
> patch [1] that a 7% performance improvement can be seen on existing
> riscv hardware by performing the extra jump. Doing tail calls should be
> avoided on riscv since the hardware can be expected to predict the
> return address incorrectly every time if the return address is manually
> changed.

 Fair enough, thanks.  Though no link to said patch given.

  Maciej