Re: [PATCH v3] riscv: entry: set a0 = -ENOSYS only when syscall != -1

[Celeste Liu]

On July 20, 2023 12:28:47 AM GMT+08:00, "Björn Töpel" <bjorn@xxxxxxxxxx> wrote:
>Andreas Schwab <schwab@xxxxxxx> 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)
>>>  
>>>  		if (syscall < NR_syscalls)
>>>  			syscall_handler(regs, syscall);
>>> -		else
>>> +		else if ((long)syscall != -1L)
>>
>> You can also use syscall != -1UL or even syscall != -1.
>
>The former is indeed better for the eyes! :-) The latter will get a
>-Wsign-compare warning, no?
>
>
>Björn

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 != -1L.