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From:   =?utf-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn@kernel.org>
To:     Celeste Liu <coelacanthushex@gmail.com>,
        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>,
        =?utf-8?B?QmrDtnJuIFTDtnBlbA==?= <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
In-Reply-To: <54D8BFF7-C4D2-417E-B18C-62B5DB17B51B@gmail.com>
References: <20230718210037.250665-1-CoelacanthusHex@gmail.com>
 <mvmo7k8cqns.fsf@suse.de> <878rbbkgqo.fsf@all.your.base.are.belong.to.us>
 <54D8BFF7-C4D2-417E-B18C-62B5DB17B51B@gmail.com>
Date:   Thu, 20 Jul 2023 11:08:37 +0200
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Celeste Liu <coelacanthushex@gmail.com> writes:

> On July 20, 2023 12:28:47 AM GMT+08:00, "Bj=C3=B6rn T=C3=B6pel" <bjorn@ke=
rnel.org> wrote:
>>Andreas Schwab <schwab@suse.de> 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=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.
>>
>>The former is indeed better for the eyes! :-) The latter will get a
>>-Wsign-compare warning, no?
>>
>>
>>Bj=C3=B6rn
>
> Well, that's true. 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. So it is really better than (long)syscall !=3D -1L.

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.