Re: [PATCH] io_uring/net: fix build warning for !CONFIG_COMPAT

[Arnd Bergmann]

On Thu, Feb 27, 2025, at 14:49, Pavel Begunkov wrote:
> On 2/27/25 13:20, Arnd Bergmann wrote:
>>        |                      ^~~
>> 
>> Since io_is_compat() turns into a compile-time 'false', the #ifdef
>> here is completely unnecessary, and removing it avoids the warning.
>
> I don't think __get_compat_msghdr() and other helpers are
> compiled for !COMPAT.

They are not defined without CONFIG_COMPAT. My point in the
message is that io_is_compat() turning into a compile-time
'false' value means that they also don't get called, because
compilers are really good at this type of dead code elimination.

> I'd just silence it like:
>
> if (io_is_compat(req->ctx)) {
> 	ret = -EFAULT;
> #ifdef CONFIG_COMPAT
> 	...
> #endif CONFIG_COMPAT
> }

That seems even less readable. If you want to be explicit
about it, you could use

     if (IS_ENABLED(CONFIG_COMPAT) && io_is_compat(req->ctx)) {

to replace the #ifdef, but as I wrote in the patch
description, the compile-time check is really redundant
because io_is_compat() is meant to do exactly that.

       Arnd