linux-kernel - Re: [PATCH v3] arm64: sysreg: make mrs_s and msr

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Date:   Tue, 16 Apr 2019 18:18:30 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Alex Matveev <alxmtvv@...il.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Yury Norov <ynorov@...iumnetworks.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] arm64: sysreg: make mrs_s and msr_s macros work with
 Clang and LTO

On Mon, Apr 15, 2019 at 10:22:27AM -0700, Nick Desaulniers wrote:
> On Mon, Apr 15, 2019 at 10:06 AM Mark Rutland <mark.rutland@....com> wrote:
> > On Mon, Apr 15, 2019 at 07:38:21AM -0700, Kees Cook wrote:
> > > diff --git a/arch/arm64/include/asm/irqflags.h b/arch/arm64/include/asm/irqflags.h
> > > index 43d8366c1e87..06d3987d1546 100644
> > > --- a/arch/arm64/include/asm/irqflags.h
> > > +++ b/arch/arm64/include/asm/irqflags.h
> > > @@ -43,7 +43,9 @@ static inline void arch_local_irq_enable(void)
> > >       asm volatile(ALTERNATIVE(
> > >               "msr    daifclr, #2             // arch_local_irq_enable\n"
> > >               "nop",
> > > +             DEFINE_MSR_S
> > >               "msr_s  " __stringify(SYS_ICC_PMR_EL1) ",%0\n"
> > > +             UNDEFINE_MSR_S
> >
> > If we do need this, can we wrap this in a larger CPP macro that does the
> > whole sequence of defining, using, and undefining the asm macros?
> 
> I agree that would be cleaner.  For example, __mrs_s/__msr_s can
> ALMOST do this (be used in arch/arm64/include/asm/irqflags.h) except
> for the input/output constraints.  Maybe the constraints can be
> removed from the cpp macro definition, then the constraints be left to
> the macro expansion sites?  That way the DEFINE_MXX_S/UNDEFINE_MXX_S
> can be hidden in the cpp macro itself.

If those took the register template explicitly, i.e. something like:

	__mrs_s(SYS_ICC_PMR_EL1, "%x0") 

	__msr_s("%[whatever]", SYS_FOO)

... that would be more generally useful and clear, as they could be used
in larger asm sequences.

Thanks,
Mark.