linux-kernel - Re: [PATCH v2] RISC-V: Don't use a global include guard for uapi/asm/syscalls.h

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Date:   Mon, 6 Aug 2018 14:00:53 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Palmer Dabbelt <palmer@...ive.com>,
        linux-riscv@...ts.infradead.org,
        Christoph Hellwig <hch@...radead.org>
Cc:     aou@...s.berkeley.edu, Arnd Bergmann <arnd@...db.de>,
        tklauser@...tanz.ch, linux-kernel@...r.kernel.org,
        Marcus Comstedt <marcus@...pp.se>
Subject: Re: [PATCH v2] RISC-V: Don't use a global include guard for
 uapi/asm/syscalls.h

On 08/06/2018 01:42 PM, 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>
> ---
>  arch/riscv/include/asm/unistd.h        |  5 +++++
>  arch/riscv/include/uapi/asm/syscalls.h | 15 +++++++++------
>  2 files changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/unistd.h b/arch/riscv/include/asm/unistd.h
> index 080fb28061de..508be1780323 100644
> --- a/arch/riscv/include/asm/unistd.h
> +++ b/arch/riscv/include/asm/unistd.h
> @@ -11,6 +11,11 @@
>   *   GNU General Public License for more details.
>   */
>  
> +/*
> + * There is explicitly no include guard here because this file is expected to

to .. be .. included

> + * included multiple times.  See uapi/asm/syscalls.h for more info.
> + */
> +
>  #define __ARCH_WANT_SYS_CLONE
>  #include <uapi/asm/unistd.h>
>  #include <uapi/asm/syscalls.h>
> diff --git a/arch/riscv/include/uapi/asm/syscalls.h b/arch/riscv/include/uapi/asm/syscalls.h
> index 818655b0d535..690beb002d1d 100644
> --- a/arch/riscv/include/uapi/asm/syscalls.h
> +++ b/arch/riscv/include/uapi/asm/syscalls.h
> @@ -1,10 +1,13 @@
> -/* 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

like that one :)

> + * __SYSCALL.
> + */
>  
>  /*
>   * Allows the instruction cache to be flushed from userspace.  Despite RISC-V


-- 
~Randy