Re: [patch V2 1/6] ARM: uaccess: Implement missing __get_user_asm_dword()

["Russell King (Oracle)" <linux@armlinux.org.uk>]

On Wed, Sep 17, 2025 at 10:14:24AM -0700, Nathan Chancellor wrote:
> On Wed, Sep 17, 2025 at 04:17:38PM +0100, Russell King (Oracle) wrote:
> > For me, this produces:
> > 
> > get-user-test.c:41:16: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
> >    41 |         (x) = *(__force __typeof__(*(ptr)) *) &__gu_val;                \
> >       |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > 
> > with arm-linux-gnueabihf-gcc (Debian 14.2.0-19) 14.2.0
> > 
> > Maybe you're using a different compiler that doesn't issue that warning?
> 
> Maybe because the kernel uses -fno-strict-aliasing, which presumably
> turns off -Wstrict-aliasing?

Thanks, I'd forgotten to pick the -f flags for building the out of tree
test. Yes, that does work, but I wonder whether the powerpc 32-bit
approach with __long_type() that Christophe mentioned would be better.
That also appears to avoid all issues, and doesn't need the use of
the nasty __force, address-of and deref trick.

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