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References: <20230403065207.1070974-1-bjorn@kernel.org>
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From:   Andy Chiu <andy.chiu@sifive.com>
Date:   Mon, 10 Apr 2023 17:41:57 +0800
Message-ID: <CABgGipVHV9C3QwsCkaU+ecTPqhdztn7EwWOr1Hc1ETqEWhhdxQ@mail.gmail.com>
Subject: Re: [PATCH] riscv: entry: Save a0 prior syscall_enter_from_user_mode()
To:     =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn@kernel.org>
Cc:     Albert Ou <aou@eecs.berkeley.edu>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        linux-riscv@lists.infradead.org,
        Guo Ren <guoren@linux.alibaba.com>,
        =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn@rivosinc.com>,
        =?UTF-8?Q?Heiko_St=C3=BCbner?= <heiko@sntech.de>,
        Conor Dooley <conor@kernel.org>,
        Yipeng Zou <zouyipeng@huawei.com>,
        linux-kernel@vger.kernel.org, Palmer Dabbelt <palmer@rivosinc.com>,
        Heiko Stuebner <heiko.stuebner@vrull.eu>
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On Mon, Apr 3, 2023 at 2:54=E2=80=AFPM Bj=C3=B6rn T=C3=B6pel <bjorn@kernel.=
org> wrote:
>
> From: Bj=C3=B6rn T=C3=B6pel <bjorn@rivosinc.com>
>
> 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.
>
> This is resolved, by saving a0 prior doing the
> syscall_enter_from_user_mode() call.
>
> Fixes: f0bddf50586d ("riscv: entry: Convert to generic entry")
> Reviewed-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
> Tested-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
> Signed-off-by: Bj=C3=B6rn T=C3=B6pel <bjorn@rivosinc.com>

This fix works for me, thanks!

Tested-by: Andy Chiu <andy.chiu@sifive.com>