Re: [bug report] Linux-2.6.12-rc2

[Dan Carpenter <dan.carpenter@linaro.org>]

On Fri, May 30, 2025 at 07:46:20AM +0200, Arnd Bergmann wrote:
> On Wed, May 28, 2025, at 10:10, Dan Carpenter wrote:
> >
> > arch/alpha/kernel/err_marvel.c:884 marvel_find_io7_with_error() warn: 
> > statement has no effect 'csrs->POx_ERR_SUM.csr'
> > arch/alpha/kernel/err_marvel.c:892 marvel_find_io7_with_error() warn: 
> > statement has no effect 'io7->csrs->PO7_ERROR_SUM.csr'
> >
> 
> > I occasionally try to run Smatch against code that I can't actually
> > compile and it found this code from before the git era.  These days
> > we build with -Wall and so this kind of code doesn't normally compile
> > on x86 or Arm.  We would get a warning like:
> >
> > test.c:18:9: warning: statement with no effect [-Wunused-value]
> >    18 |         x;
> >       |         ^
> >
> > So it makes me wonder if this code can actually build?
> >
> 
> FWIW, I tried building the file with gcc-15 and don't see a
> warning for that construct, even with the -Wextra.
> 
> After digging around some more, I found that this is the
> definition of the structure, and that the 'volatile' in there
> causes gcc and clang to not consider the statement to be
> free of side-effects. I assume it will actually cause a
> load from an MMIO register here:
> 
> typedef struct {
>  volatile unsigned long csr __attribute__((aligned(64)));
> } io7_csr;

Huh.  Thanks, Arnd.  I hadn't even considered that.

regards,
dan carpenter