Re: [PATCH v3] arm64: sysreg: make mrs_s and msr_s macros work with Clang and LTO

[Ard Biesheuvel]

On Wed, 24 Apr 2019 at 00:55, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> On Mon, Apr 15, 2019 at 7:38 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> > +#define __msr_s(r, v)                                          \
> > +       DEFINE_MSR_S                                            \
> > +"      msr_s " __stringify(r) ", %x0\n"                        \
> > +       UNDEFINE_MSR_S : : "rZ" (v)
>
> BTW ... is "%x0" a typo here? Shouldn't this just be "%0"?
>

No, iirc, that is required to force clang to choose a x# encoding
(which is the only one supported by msr/mrs instructions). Otherwise,
it will infer from the operand size which encoding to use, and attempt
to use w# for 32-bit system registers.