Re: [PATCH 5.10.y 5.15.y 6.1.y 6.6.y 6.12.y 6.18.y 6.19.y] ARM: clean up the memset64() C wrapper

[Greg KH <greg@kroah.com>]

On Wed, Feb 25, 2026 at 04:08:23PM +0100, Thomas Weißschuh wrote:
> On Wed, Feb 25, 2026 at 06:36:13AM -0800, Greg KH wrote:
> > On Wed, Feb 25, 2026 at 12:35:09PM +0100, Thomas Weißschuh wrote:
> > > [ Upstream commit b52343d1cb47bb27ca32a3f4952cc2fd3cd165bf ]
> > > 
> > > The current logic to split the 64-bit argument into its 32-bit halves is
> > > byte-order specific and a bit clunky.  Use a union instead which is
> > > easier to read and works in all cases.
> > > 
> > > GCC still generates the same machine code.
> > > 
> > > While at it, rename the arguments of the __memset64() prototype to
> > > actually reflect their semantics.
> > > 
> > > Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
> > > Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> > > Reported-by: Ben Hutchings <ben@decadent.org.uk> # for -stable
> > > Link: https://lore.kernel.org/all/1a11526ae3d8664f705b541b8d6ea57b847b49a8.camel@decadent.org.uk/
> > > Suggested-by: https://lore.kernel.org/all/aZonkWMwpbFhzDJq@casper.infradead.org/ # for -stable
> > > Link: https://lore.kernel.org/all/aZonkWMwpbFhzDJq@casper.infradead.org/
> > > ---
> > > Hi stable team,
> > > 
> > > unfortunately the backports of commit 23ea2a4c7232 ("ARM: 9468/1: fix
> > > memset64() on big-endian") does not work on 5.10 and 5.15 as
> > > CONFIG_CPU_LITTLE_ENDIAN does not exist there, effectively breaking memset64()
> > > on little-endian. Please use this variant instead which always works.
> > > For consistency I prefer to have it backported to all versions.
> > > ---
> > >  arch/arm/include/asm/string.h | 14 +++++++++-----
> > >  1 file changed, 9 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/arch/arm/include/asm/string.h b/arch/arm/include/asm/string.h
> > > index b5ad23acb303..369781ec5511 100644
> > > --- a/arch/arm/include/asm/string.h
> > > +++ b/arch/arm/include/asm/string.h
> > > @@ -33,13 +33,17 @@ static inline void *memset32(uint32_t *p, uint32_t v, __kernel_size_t n)
> > >  }
> > >  
> > >  #define __HAVE_ARCH_MEMSET64
> > > -extern void *__memset64(uint64_t *, uint32_t low, __kernel_size_t, uint32_t hi);
> > > +extern void *__memset64(uint64_t *, uint32_t first, __kernel_size_t, uint32_t second);
> > >  static inline void *memset64(uint64_t *p, uint64_t v, __kernel_size_t n)
> > >  {
> > > -	if (IS_ENABLED(CONFIG_CPU_LITTLE_ENDIAN))
> > > -		return __memset64(p, v, n * 8, v >> 32);
> > > -	else
> > > -		return __memset64(p, v >> 32, n * 8, v);
> > > +	union {
> > > +		uint64_t val;
> > > +		struct {
> > > +			uint32_t first, second;
> > > +		};
> > > +	} word = { .val = v };
> > > +
> > > +	return __memset64(p, word.first, n * 8, word.second);
> > >  }
> > >  
> > >  #endif
> > > 
> > > ---
> > 
> > I don't understand, why is this patch needed at all?  What issue is it
> > fixing to require this?
> 
> memset64() was broken on ARM big-endian. It was fixed in commit 23ea2a4c7232
> ("ARM: 9468/1: fix memset64() on big-endian"). That fix was marked with a Fixes:
> tag and was backported to all stable kernels. However that fix relies on the
> kconfig symbol CONFIG_CPU_LITTLE_ENDIAN (as shown in the diff above).
> That kconfig symbol does not exist on 5.10 and 5.15. So now memset64() is
> broken on ARM little-endian on those branches.

So on ALL branches?  When did that config option get added?

> The proposed works always, without requiring kconfig options.
> The Fixes: tag target would differ between the stable branches,
> so I left it out.

A fixes: for commit 23ea2a4c7232 should be correct, right?

thanks,

greg k-h