Re: [Bug report] __arch_hweight32/64 x86

[Sebastian Sumpf]

On 6/27/23 06:25, Borislav Petkov wrote:
> On Mon, Jun 26, 2023 at 03:41:27PM -0700, Dave Hansen wrote:
> > I'm not even sure that UML needs GENERIC_HWEIGHT.  From a quick glance,
> > it looks like x86 used to use GENERIC_HWEIGHT, but got arch-specific
> > versions later.  UML just never moved over to the arch-specific versions.
>
> Thanks - that could very well be the explanation.
>
> That bug report made me blink a couple of times since I did take extra
> precaution to not clobber regs in arch/x86/lib/hweight.S as this was
> part of the whole pain back then with calling a function from asm where
> gcc doesn't even know we're calling a function, see:
>
> f5967101e9de ("x86/hweight: Get rid of the special calling convention")
>
> > I _think_ the attached patch might just fix the problems with the C
> > version and bring the x86/UML implementation back in line with the rest
> > of x86.
> >
> > Thoughts?
>
> > diff --git a/arch/x86/um/Kconfig b/arch/x86/um/Kconfig
> > index 186f13268401..76d507860be4 100644
> > --- a/arch/x86/um/Kconfig
> > +++ b/arch/x86/um/Kconfig
> > @@ -44,6 +44,3 @@ config ARCH_HAS_SC_SIGNALS
> >   
> >   config ARCH_REUSE_HOST_VSYSCALL_AREA
> >   	def_bool !64BIT
> > -
> > -config GENERIC_HWEIGHT
> > -	def_bool y
>
> Yeah, we should do it. UML should not do anything different wrt calling
> conventions so it should be able to handle the arch/x86/lib/hweight.S
> versions just fine.

Thank you for the quick resolution! It fixes the problem for me and sorry for 
not explaining well enough.

> Richi?

--
Sebastian Sumpf
Genode Labs

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