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, 06 Aug 2018 17:11:10 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     rdunlap@...radead.org
CC:     linux-riscv@...ts.infradead.org,
        Christoph Hellwig <hch@...radead.org>, aou@...s.berkeley.edu,
        Arnd Bergmann <arnd@...db.de>, tklauser@...tanz.ch,
        linux-kernel@...r.kernel.org, marcus@...pp.se
Subject:     Re: [PATCH v2] RISC-V: Don't use a global include guard for uapi/asm/syscalls.h

On Mon, 06 Aug 2018 14:00:53 PDT (-0700), rdunlap@...radead.org wrote:
> 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

Thanks.  I'm not going to spin a v3 unless there's more feedback, but I'll 
include it in the PR.

>
>> + * 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