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From:   Celeste Liu <coelacanthushex@gmail.com>
Date:   Thu, 20 Jul 2023 14:46:03 +0800
To:     =?ISO-8859-1?Q?Bj=F6rn_T=F6pel?= <bjorn@kernel.org>,
        Andreas Schwab <schwab@suse.de>
CC:     Palmer Dabbelt <palmer@rivosinc.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Albert Ou <aou@eecs.berkeley.edu>, Guo Ren <guoren@kernel.org>,
        =?ISO-8859-1?Q?Bj=F6rn_T=F6pel?= <bjorn@rivosinc.com>,
        Conor Dooley <conor.dooley@microchip.com>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        Felix Yan <felixonmars@archlinux.org>,
        Ruizhe Pan <c141028@gmail.com>,
        Shiqi Zhang <shiqi@isrc.iscas.ac.cn>
Subject: Re: [PATCH v3] riscv: entry: set a0 = -ENOSYS only when syscall != -1
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On July 20, 2023 12:28:47 AM GMT+08:00, "Bj=C3=B6rn T=C3=B6pel" <bjorn@kern=
el=2Eorg> wrote:
>Andreas Schwab <schwab@suse=2Ede> writes:
>
>> On Jul 19 2023, Celeste Liu wrote:
>>
>>> @@ -308,7 +312,7 @@ asmlinkage __visible __trap_section void do_trap_e=
call_u(struct pt_regs *regs)
>>> =20
>>>  		if (syscall < NR_syscalls)
>>>  			syscall_handler(regs, syscall);
>>> -		else
>>> +		else if ((long)syscall !=3D -1L)
>>
>> You can also use syscall !=3D -1UL or even syscall !=3D -1=2E
>
>The former is indeed better for the eyes! :-) The latter will get a
>-Wsign-compare warning, no?
>
>
>Bj=C3=B6rn

Well, that's true=2E And I just found out that by C standards, converting
ulong to long is implementation-defined behavior, unlike long to ulong
which is well-defined=2E So it is really better than (long)syscall !=3D -1=
L=2E