[PATCH][BZ 17979][BZ 17721] Fix issues with sys/cdefs.h and uchar.h when using non-gcc compiler.

[Joseph Myers]

On Thu, 28 Jan 2016, Mike Frysinger wrote:

> On 28 Jan 2016 22:52, Joseph Myers wrote:
> > On Thu, 28 Jan 2016, Dwight Guth wrote:
> > > Okay but if so, then why put the __restrict in the header files at all
> > > if it doesn't really matter? And why put it there only if the compiler
> > > is gcc?
> > 
> > Effectively it serves as documentation of intent for people reading the 
> > headers (much like the argument names with __ prefixes).
> 
> wouldn't it also assist automated tools like linters/static analyzers ?

If they hardcode information about particular functions, the qualifiers in 
the headers are irrelevant.  If not, even having restrict qualifiers on 
the parameters in the function definitions is only useful when you look at 
the body of the definitions as well, unless you apply heuristics beyond 
what is supported by the standard.

Remember that if a function has two restricted pointer arguments (that are 
restricted in the definition), this does *not* mean that they don't alias 
- only that *if* a particular execution of the function modifies some 
elements pointed to by one of the pointers, those elements are not also 
accessed other than through that pointer.  (But it's completely valid to 
have two restricted pointers to the same array, one only used to access / 
modify odd-numbered elements of that array, and the other one only used to 
access / modify even-numbered elements of that array.  Now, static 
analyzers might reasonably consider that dubious usage that should be 
diagnosed.)

-- 
Joseph S. Myers
joseph@codesourcery.com