linux-kernel - Re: [PATCH] RISC-V: Don't use a global include guard for uapi/asm/syscalls.h

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Date:   Thu, 9 Aug 2018 06:26:12 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Palmer Dabbelt <palmer@...ive.com>
Cc:     linux-riscv@...ts.infradead.org, aou@...s.berkeley.edu,
        linux-kernel@...r.kernel.org, Marcus Comstedt <marcus@...pp.se>
Subject: Re: [PATCH] RISC-V: Don't use a global include guard for
 uapi/asm/syscalls.h

On Fri, Aug 03, 2018 at 12:53:44PM -0700, Palmer Dabbelt wrote:
> This file is expected to be included multiple times in the same file in
> order to allow the __SYSCALL macro to generate system call tables.  With
> a global include guard we end up missing __NR_riscv_flush_icache in the
> syscall table, which results in icache flushes that escape the vDSO call
> to not actually do anything.
> 
> The fix is to move to per-#define include guards, which allows the
> system call tables to actually be populated.  Thanks to Macrus Comstedt
> for finding and fixing the bug!
> 
> I also went ahead and fixed the SPDX header to use a //-style comment,
> which I've been told is the canonical way to do it.
> 
> Cc: Marcus Comstedt <marcus@...pp.se>
> Signed-off-by: Palmer Dabbelt <palmer@...ive.com>

Fails to build riscv:allnoconfig.

CC      arch/riscv/kernel/syscall_table.o
./arch/riscv/include/uapi/asm/syscalls.h:29:36: error:
‘sys_riscv_flush_icache’ undeclared here (not in a function); did you mean ‘__NR_riscv_flush_icache’?

Guenter

> ---
>  arch/riscv/include/uapi/asm/syscalls.h | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/riscv/include/uapi/asm/syscalls.h b/arch/riscv/include/uapi/asm/syscalls.h
> index 818655b0d535..882a6aa09a33 100644
> --- a/arch/riscv/include/uapi/asm/syscalls.h
> +++ b/arch/riscv/include/uapi/asm/syscalls.h
> @@ -1,10 +1,11 @@
> -/* SPDX-License-Identifier: GPL-2.0 */
> +// SPDX-License-Identifier: GPL-2.0
>  /*
> - * Copyright (C) 2017 SiFive
> + * Copyright (C) 2017-2018 SiFive
>   */
>  
> -#ifndef _ASM__UAPI__SYSCALLS_H
> -#define _ASM__UAPI__SYSCALLS_H
> +/* There is explicitly no include guard here because this file is expected to
> + * be included multiple times in order to define the syscall macros via
> + * __SYSCALL. */
>  
>  /*
>   * Allows the instruction cache to be flushed from userspace.  Despite RISC-V
> @@ -20,7 +21,7 @@
>   * caller.  We don't currently do anything with the address range, that's just
>   * in there for forwards compatibility.
>   */
> +#ifndef __NR_riscv_flush_icache
>  #define __NR_riscv_flush_icache (__NR_arch_specific_syscall + 15)
> -__SYSCALL(__NR_riscv_flush_icache, sys_riscv_flush_icache)
> -
>  #endif
> +__SYSCALL(__NR_riscv_flush_icache, sys_riscv_flush_icache)