Re: [PATCH V5 13/21] riscv: compat: process: Add UXL_32 support in start_thread

Palmer Dabbelt
2022-02-23T01:43:02Z

On Tue, 01 Feb 2022 07:05:37 PST (-0800), guoren@kernel.org wrote:
> From: Guo Ren <guoren@linux.alibaba.com>
>
> If the current task is in COMPAT mode, set SR_UXL_32 in status for
> returning userspace. We need CONFIG _COMPAT to prevent compiling
> errors with rv32 defconfig.
>
> Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> Signed-off-by: Guo Ren <guoren@kernel.org>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Palmer Dabbelt <palmer@dabbelt.com>
> ---
> arch/riscv/kernel/process.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
> index 03ac3aa611f5..1a666ad299b4 100644
> --- a/arch/riscv/kernel/process.c
> +++ b/arch/riscv/kernel/process.c
> @@ -97,6 +97,11 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
> }
> regs->epc = pc;
> regs->sp = sp;
> +
> +#ifdef CONFIG_COMPAT
> + if (is_compat_task())
> + regs->status |= SR_UXL_32;

Not sure if I'm just misunderstanding the bit ops here, but aren't we
trying to set the UXL field to 1 (for UXL=32)? That should be a bit
field set op, not just an OR.

> +#endif
> }
>
> void flush_thread(void)

Additionally: this isn't really an issue so much with this patch, but it
does bring up that we're relying on someone else to have set UXL=64 on
CONFIG_COMPAT=n systems. I don't see that in any spec anywhere, so we
should really be setting UXL in Linux for all systems (ie, not just those with
COMPAT=y).