linux-kernel - Re: [PATCH] riscv: add asm/unistd.h UAPI header

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Date:   Tue, 06 Nov 2018 16:08:12 -0800 (PST)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     david.abdurachmanov@...il.com, aou@...s.berkeley.edu,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        marcin.juszkiewicz@...aro.org, linux@...ck-us.net
Subject:     Re: [PATCH] riscv: add asm/unistd.h UAPI header

On Mon, 05 Nov 2018 12:56:15 PST (-0800), Arnd Bergmann wrote:
> On 11/5/18, David Abdurachmanov <david.abdurachmanov@...il.com> wrote:
>> Marcin Juszkiewicz reported issues while generating syscall table for riscv
>> using 4.20-rc1. The patch refactors our unistd.h files to match some other
>> architectures.
>>
>> - Add asm/unistd.h UAPI header, which has __ARCH_WANT_NEW_STAT
>> - Remove asm/syscalls.h UAPI header and merge to asm/unistd.h
>> - Adjust kernel asm/unistd.h
>>
>> So now asm/unistd.h UAPI header should show all syscalls for riscv.
>>
>> Before this, Makefile simply put `#include <asm-generic/unistd.h>` into
>> generated asm/unistd.h UAPI header thus user didn't see:
>>
>> - __NR_riscv_flush_icache
>> - __NR_newfstatat
>> - __NR_fstat
>>
>> which are supported by riscv kernel.
>>
>> Signed-off-by: David Abdurachmanov <david.abdurachmanov@...il.com>
>> Cc: Arnd Bergmann <arnd@...db.de>
>> Cc: Marcin Juszkiewicz <marcin.juszkiewicz@...aro.org>
>> Cc: Guenter Roeck <linux@...ck-us.net>
>
> Thanks for addressing this, your patch correctly fixes riscv64, and
> I should have noticed the mistake when I originally merged the
> broken patch.
>
> However, looking closer I found another problem with the original
> patch that your fix does not address:
>
> __ARCH_WANT_NEW_STAT should only be set on 64-bit
> architectures.
>
> For a 32-bit architecture, we only want __ARCH_WANT_STAT64 if
> any. For 64-bit architectures with compat mode, we still need to
> set __ARCH_WANT_STAT64 from the non-uapi file so we get
> the syscall implementation.
>
> If we don't care about the riscv32 ABI changing yet, we can
> decide to leave out __ARCH_WANT_STAT64 here, and require
> glibc to implement it using statx() like any new architecture.
> stat64 is not y2038 safe, and statx replaces it because of that.

Thanks for pointing this out.   A while ago we decided the rv32 ABI was 
"slushy": it can change if it has a good reason to.  Right now the only planned 
changes are the y2038 changes, which I consider this a part of.  For some 
reason I thought we'd already done this, but since we haven't then I think it 
should go in sooner rather than later -- that will help the glibc guys get 
everything lined up.

The target is still the next glibc release (Feb 1st) for a stable RV32I ABI.  
That's progressing well, with one last blocking issue related to some of our 
floating-point emulation routines before we can submit the port.  This should 
give us ample time to line up the ABIs correctly so everything works.

So I think the correct answer here is to drop __ARCH_WANT_STAT64 from RISC-V.

>> Fixes: 67314ec7b025
>
> That line should be formatted as
>
> Fixes: 67314ec7b025 ("RISC-V: Request newstat syscalls")

Yep, and I have 

[pretty]
	fixes = Fixes: %h (\"%s\")

to make that slightly easier for me to remember :).