Re: outb(2): terminology correction

[Alejandro Colomar <alx@kernel.org>]

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[CC += GENERIC INCLUDE/ASM HEADER FILES maintainers]

Hi astian, Arnd,

> Date: 2026-08-31 09:09:46+0000
> From: astian <astian@memeware.net>
>
> outb(2) says:
> 
>   You must compile with -O or -O2 or similar.  The functions are defined
>   as inline macros, and will not be substituted in without optimization
>   enabled, causing unresolved references at link time.
> 
> "inline macros [...] not substituted in without optimization" doesn't
> make any sense.  C pre-processor macros cannot be inline or not inline.
> Indeed these are inline *functions* (at least in this system) with
> embedded assembly apparently referencing parameters (which, I surmise,
> is why the functions need to be inlined by the compiler or the assembly
> will not work).
> 
> From /usr/include/x86_64-linux-gnu/sys/io.h (glibc 2.43):
> 
>   [...]
>   #if defined __GNUC__ && __GNUC__ >= 2
> 
>   static __inline unsigned char
>   inb (unsigned short int __port)
>   {
>     unsigned char _v;
> 
>     __asm__ __volatile__ ("inb %w1,%0":"=a" (_v):"Nd" (__port));
>     return _v;
>   }
> 
>   [...]
> 
>   static __inline void
>   outb (unsigned char __value, unsigned short int __port)
>   {
>     __asm__ __volatile__ ("outb %b0,%w1": :"a" (__value), "Nd" (__port));
>   }
> 
>   [...]
> 
> So I would say just s/inline macros/inline functions/g.

Yes, 'inline functions' seems more appropriate than 'inline macros' (all
macros are inlined, due to how the preprocessor works, so they'd be just
macros, and as you showed, these are not even macros --except maybe in
some architectures--).

However, I doubt the entire paragraph.  I don't know why inline
functions would produce unresolved references at link time _even if they
were not substituted_.  The point of inline functions is that they are
sometimes inlined, and sometimes not, and the compiler does the right
thing in both cases.

This seems like paranoia from decades ago, when inline functions were
less known (and maybe compilers were more buggy than they are now).

Arnd, should we remove the paragraph entirely?  Or is there any obscure
reason why optimizations are required?


Have a lovely day!
Alex 

-- 
<https://www.alejandro-colomar.es>

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