linux-kernel - Re: [PATCH] riscv: entry: Save a0 prior syscall_enter_from_user

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Message-Id: <168123475135.4147.9051999374596978440.b4-ty@rivosinc.com>
Date:   Tue, 11 Apr 2023 10:39:11 -0700
From:   Palmer Dabbelt <palmer@...osinc.com>
To:     Albert Ou <aou@...s.berkeley.edu>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        linux-riscv@...ts.infradead.org, Guo Ren <guoren@...nel.org>,
        =C3=B6rn_T=C3=B6pel?= <bjorn@...nel.org>
Cc:     =C3=B6rn_T=C3=B6pel?= <bjorn@...osinc.com>,
        iko_St=C3=BCbner?= <heiko@...ech.de>,
        Conor Dooley <conor@...nel.org>,
        Yipeng Zou <zouyipeng@...wei.com>,
        linux-kernel@...r.kernel.org,
        Heiko Stuebner <heiko.stuebner@...ll.eu>
Subject: Re: [PATCH] riscv: entry: Save a0 prior
 syscall_enter_from_user_mode()


On Mon, 03 Apr 2023 08:52:07 +0200, Björn Töpel wrote:
> The RISC-V calling convention passes the first argument, and the
> return value in the a0 register. For this reason, the a0 register
> needs some extra care; When handling syscalls, the a0 register is
> saved into regs->orig_a0, so a0 can be properly restored for,
> e.g. interrupted syscalls.
> 
> This functionality was broken with the introduction of the generic
> entry patches. Here, a0 was saved into orig_a0 after calling
> syscall_enter_from_user_mode(), which can change regs->a0 for some
> paths, incorrectly restoring a0.
> 
> [...]

Applied, thanks!

[1/1] riscv: entry: Save a0 prior syscall_enter_from_user_mode()
      https://git.kernel.org/palmer/c/9c2598d43510

Best regards,
-- 
Palmer Dabbelt <palmer@...osinc.com>