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From:   Celeste Liu <coelacanthushex@gmail.com>
Date:   Fri, 21 Jul 2023 03:24:08 +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 5:08:37 PM GMT+08:00, "Bj=C3=B6rn T=C3=B6pel" <bjorn@kerne=
l=2Eorg> wrote:
>Celeste Liu <coelacanthushex@gmail=2Ecom> writes:
>
>> On July 20, 2023 12:28:47 AM GMT+08:00, "Bj=C3=B6rn T=C3=B6pel" <bjorn@=
kernel=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=
_ecall_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, converti=
ng
>> 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=
 -1L=2E
>
>If you're respinning, I suggest you use David's suggestion:
> * Remove the comment I suggest you to add
> * Use (signed) long
> * Add syscall >=3D 0 &&
> * else if (syscall !=3D -1)
>
>Which is the least amount of surprises IMO=2E

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