linux-kernel - Re: [PATCH V5 12/21] riscv: compat: syscall: Add entry.S implementation

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Date:   Tue, 22 Feb 2022 17:42:50 -0800 (PST)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     guoren@...nel.org
CC:     guoren@...nel.org, Arnd Bergmann <arnd@...db.de>,
        anup@...infault.org, Greg KH <gregkh@...uxfoundation.org>,
        liush@...winnertech.com, wefu@...hat.com, drew@...gleboard.org,
        wangjunqiang@...as.ac.cn, Christoph Hellwig <hch@....de>,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-csky@...r.kernel.org,
        linux-s390@...r.kernel.org, sparclinux@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-parisc@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        x86@...nel.org, guoren@...ux.alibaba.com
Subject:     Re: [PATCH V5 12/21] riscv: compat: syscall: Add entry.S implementation

On Tue, 01 Feb 2022 07:05:36 PST (-0800), guoren@...nel.org wrote:
> From: Guo Ren <guoren@...ux.alibaba.com>
>
> Implement the entry of compat_sys_call_table[] in asm. Ref to
> riscv-privileged spec 4.1.1 Supervisor Status Register (sstatus):
>
>  BIT[32:33] = UXL[1:0]:
>  - 1:32
>  - 2:64
>  - 3:128
>
> Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
> Signed-off-by: Guo Ren <guoren@...nel.org>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Palmer Dabbelt <palmer@...belt.com>
> ---
>  arch/riscv/include/asm/csr.h |  7 +++++++
>  arch/riscv/kernel/entry.S    | 18 ++++++++++++++++--
>  2 files changed, 23 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h
> index ae711692eec9..eed96fa62d66 100644
> --- a/arch/riscv/include/asm/csr.h
> +++ b/arch/riscv/include/asm/csr.h
> @@ -36,6 +36,13 @@
>  #define SR_SD		_AC(0x8000000000000000, UL) /* FS/XS dirty */
>  #endif
>
> +#ifdef CONFIG_COMPAT
> +#define SR_UXL		_AC(0x300000000, UL) /* XLEN mask for U-mode */
> +#define SR_UXL_32	_AC(0x100000000, UL) /* XLEN = 32 for U-mode */
> +#define SR_UXL_64	_AC(0x200000000, UL) /* XLEN = 64 for U-mode */
> +#define SR_UXL_SHIFT	32
> +#endif
> +
>  /* SATP flags */
>  #ifndef CONFIG_64BIT
>  #define SATP_PPN	_AC(0x003FFFFF, UL)
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index ed29e9c8f660..1951743f09b3 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S
> @@ -207,13 +207,27 @@ check_syscall_nr:
>  	 * Syscall number held in a7.
>  	 * If syscall number is above allowed value, redirect to ni_syscall.
>  	 */
> -	bgeu a7, t0, 1f
> +	bgeu a7, t0, 3f
> +#ifdef CONFIG_COMPAT
> +	REG_L s0, PT_STATUS(sp)
> +	srli s0, s0, SR_UXL_SHIFT
> +	andi s0, s0, (SR_UXL >> SR_UXL_SHIFT)
> +	li t0, (SR_UXL_32 >> SR_UXL_SHIFT)
> +	sub t0, s0, t0
> +	bnez t0, 1f
> +
> +	/* Call compat_syscall */
> +	la s0, compat_sys_call_table
> +	j 2f
> +1:
> +#endif
>  	/* Call syscall */
>  	la s0, sys_call_table
> +2:
>  	slli t0, a7, RISCV_LGPTR
>  	add s0, s0, t0
>  	REG_L s0, 0(s0)
> -1:
> +3:
>  	jalr s0
>
>  ret_from_syscall:

Reviewed-by: Palmer Dabbelt <palmer@...osinc.com>