Re: [PATCH v2 12/13] tools/nolibc: add __nolibc_static_assert()

["Thomas Weißschuh" <linux@weissschuh.net>]

On 2025-12-03 20:23:30+0100, Willy Tarreau wrote:
> On Wed, Dec 03, 2025 at 08:19:13PM +0100, Thomas Weißschuh wrote:
> > On 2025-11-30 12:08:56+0100, Willy Tarreau wrote:
> > > On Sat, Nov 22, 2025 at 05:59:18PM +0100, Thomas Weißschuh wrote:
> > > > Add a wrapper for _Static_assert() to use within nolibc.
> > > > While _Static_assert() itself was only standardized in C11,
> > > > in GCC and clang dialects it is also available in older standards.
> > > > 
> > > > If it turns out that _Static_assert can't be used in some contexts,
> > > > this wrapper can be adapted.
> > > > 
> > > > Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> > > > ---
> > > >  tools/include/nolibc/compiler.h | 2 ++
> > > >  1 file changed, 2 insertions(+)
> > > > 
> > > > diff --git a/tools/include/nolibc/compiler.h b/tools/include/nolibc/compiler.h
> > > > index 87090bbc53e0..ef247e916552 100644
> > > > --- a/tools/include/nolibc/compiler.h
> > > > +++ b/tools/include/nolibc/compiler.h
> > > > @@ -47,4 +47,6 @@
> > > >  #  define __nolibc_fallthrough do { } while (0)
> > > >  #endif /* __nolibc_has_attribute(fallthrough) */
> > > >  
> > > > +#define __nolibc_static_assert(_t) _Static_assert(_t, "")
> > > 
> > > I'm not super fan of raising the bar to adoption by introducing forced
> > > C11-isms, especially when they're only used to perform extra safety
> > > checks that likely remain fine after you've checked them once. What
> > > about instead:
> > > 
> > > +#if __STDC_VERSION__ >= 201112L
> > > +# define __nolibc_static_assert(_t) _Static_assert(_t, "")
> > > +#endif
> > > +# define __nolibc_static_assert(_t) do { } while (0)
> > > +#else
> > > 
> > > Note that this won't work out of code blocks but we very likely don't
> > > care. And if we'd care, we could always switch to __asm__("") which
> > > works everywhere.
> > >  
> > > What do you think ?
> > 
> > That works. But it won't be evaluated when not building with C11.
> > Which would not make it trigger when building nolibc-test.
> > So I don't want to guard it behind __STDC_VERSION__. But so far I was
> > not able to find a better, more dynamic guard. I'll look again.
> > Non-standard _Static_assert() is supported since GCC 4.6 and clang 3.0.
> 
> Fine, then we can just have a compiler version check as well, even a rough
> one, since we don't reallly care about static asserts for pretty old or
> uncommon versions, but for the modern ones that are used by developers
> and test systems.
> 
> I'd suggest going the easy route for now by checking for GCC major >= 5
> or clang major >= 3 and be done with it.

Ack. Let's do that.


Thomas