[PATCH] riscv: entry: Save a0 prior syscall_enter_from_user_mode()

[Andy Chiu]

On Mon, Apr 3, 2023 at 2:54 PM Björn Töpel <bjorn at kernel.org> wrote:
>
> From: Björn Töpel <bjorn at 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 at vrull.eu>
> Tested-by: Heiko Stuebner <heiko.stuebner at vrull.eu>
> Signed-off-by: Björn Töpel <bjorn at rivosinc.com>

This fix works for me, thanks!

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