Re: [PATCH v2 3/3] io: Add FORTIFY_SOURCE check for fcntl arguments

[Florian Weimer <fweimer@redhat.com>]

* Sergey Bugaev:

> Hello,
>
> On Tue, May 30, 2023 at 10:41 AM Florian Weimer <fweimer@redhat.com> wrote:
>> The noinline attribute does exactly what it says: it prevents inlining,
>> but it does not prevent inter-procedural analysis.  So if a function
>> returns a constrant, the compiler will still use that constant
>> elsewhere.  Newer GCC versions support the noipa attribute.  If you drop
>> the static, you can use the weak attribute for compatibility with pretty
>> much all GCC versions.
>>
>> But I think using volatile (without noinline for clarity) is fine here.
>
> So do I read this right that you're saying I should just do
>
> static int
> hide_constant (int value)
> {
>   volatile int v = value;
>   return v;
> }
>
> ? After the yesterday's discussion with Adhemerval, I was thinking of doing
>
> static inline int
> hide_constant (int value)
> {
>   asm ("" : "+rm" (value));
>   return value;
> }
>
> This does *not* prevent the whole computation from being optimized out
> if the result is unused (i.e. there's no 'volatile'), but it does
> prevent the compiler from assuming anything about the return value.

I think both variants are fine in this case.  If Adhemerval prefers the
second, please use that.

Thanks,
Florian