linux-kernel - Re: [PATCH v2] lib/crypto: riscv/chacha: Avoid s0/fp register

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Message-ID: <20251208230911.GA1853@quark>
Date: Mon, 8 Dec 2025 15:09:11 -0800
From: Eric Biggers <ebiggers@...nel.org>
To: Vivian Wang <wangruikang@...as.ac.cn>
Cc: Jerry Shih <jerry.shih@...ive.com>,
	"Jason A. Donenfeld" <Jason@...c4.com>,
	Ard Biesheuvel <ardb@...nel.org>, Paul Walmsley <pjw@...nel.org>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>, Alexandre Ghiti <alex@...ti.fr>,
	linux-crypto@...r.kernel.org, linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] lib/crypto: riscv/chacha: Avoid s0/fp register

On Tue, Dec 02, 2025 at 01:25:07PM +0800, Vivian Wang wrote:
> In chacha_zvkb, avoid using the s0 register, which is the frame pointer,
> by reallocating KEY0 to t5. This makes stack traces available if e.g. a
> crash happens in chacha_zvkb.
> 
> No frame pointer maintenence is otherwise required since this is a leaf
> function.
> 
> Signed-off-by: Vivian Wang <wangruikang@...as.ac.cn>
> ---
> Changes in v2:
> - Remove frame pointer maintenance, and simply avoid touching s0. Since
>   this is a leaf function, this also allows unwinding to work.
> - Link to v1: https://lore.kernel.org/r/20251130-riscv-chacha_zvkb-fp-v1-1-68ef7a6d477a@iscas.ac.cn
> ---
> 

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git/log/?h=libcrypto-fixes

- Eric