Re: [PATCH 2/3] selftests/nolibc: cast execve() argv string to character pointer

[David Laight <david.laight.linux@gmail.com>]

On Fri, 22 May 2026 16:39:58 +0200
Thomas Weißschuh <linux@weissschuh.net> wrote:

> On 2026-05-21 19:15:58+0100, David Laight wrote:
> > On Thu, 21 May 2026 18:29:30 +0200
> > Thomas Weißschuh <linux@weissschuh.net> wrote:
> >   
> > > The existing code would trigger a warning under -Wwrite-strings which is
> > > about to be enabled. execve() is specified as not modifying the argv
> > > array, but the exact semantics are not representable in the type system.  
> > 
> > I suspect you'll have to fix it again to avoid 'casting away const'.  
> 
> Where would this warning be coming from? Which compiler flags are needed?
> Afaik it is legal to cast away const.

IIRC -Wcast-qual
Lots of things are legal :-)
The problem with enabling -Wcast-qual (NetBSD's kernel does/did) it is makes
life annoying when you really do have to do it.
(From what I remember there weren't really that many.)
You sort of want an (unconst foo *) cast that won't generate a warning when
a simple (foo *) cast would.

> > Can you use something like (char[]){"/"} ?  
> 
> That looks good. However if this issue is real we will also have it in
> nolibc's errno.h. There I don't want to use this pattern, as it requires
> more memory.

You can move a string from .rodata to .data easily enough.
Doesn't change the memory footprint.

Not relevant for nolibc, but initialising a short string on stack
may well be faster than accessing the same string in .rodata because
of the missed caches miss (if you get what I mean).

-- David

> 
> (...)
> 
> 
> Thomas