Re: [PATCH] docs: add extra integer types to printk-formats

[Joe Perches]

On Tue, 2019-03-05 at 12:07 -0800, Matthew Wilcox wrote:
> On Tue, Mar 05, 2019 at 11:59:30AM -0800, Joe Perches wrote:
> > Many of the -Wformat warnings are bogus too.
> > 
> > There's nothing wrong with using %x for a unsigned int
> > of less than long size. (u8/u16)
> 
> I believe you to be incorrect.
> 
> 6.5.2.2 Function calls
> 
> 7 If the expression that denotes the called function has a type that does
>   include a prototype, the arguments are implicitly converted, as if by
>   assignment, to the types of the corresponding parameters, taking the
>   type of each parameter to be the unqualified version of its declared
>   type. The ellipsis notation in a function prototype declarator causes
>   argument type conversion to stop after the last declared parameter. The
>   default argument promotions are performed on trailing arguments.

Look at default argument promotions for varargs functions.
(integer promotions)

> I could define a calling convention for my CPU which says to pack u8s
> and u16s as tightly as possible in registers (or on the stack), rather
> than the prevailing calling convention of having each argument take up
> at least one register-sized slot.

Doesn't matter for varargs.  See above.

cheers, Joe