Re: [PATCH v6 3/3] x86: paravirt: make native_save_fl extern inline

Ingo Molnar
2018-06-26T07:13:25Z

* Nick Desaulniers <ndesaulniers@google.com> wrote:

> On Thu, Jun 21, 2018 at 7:24 PM Ingo Molnar <mingo@kernel.org> wrote:
> > * Nick Desaulniers <ndesaulniers@google.com> wrote:
> >
> > > native_save_fl() is marked static inline, but by using it as
> > > a function pointer in arch/x86/kernel/paravirt.c, it MUST be outlined.
> >
> > > --- a/arch/x86/include/asm/irqflags.h
> > > +++ b/arch/x86/include/asm/irqflags.h
> > > @@ -13,7 +13,7 @@
> > > * Interrupt control:
> > > */
> > >
> > > -static inline unsigned long native_save_fl(void)
> > > +extern inline unsigned long native_save_fl(void)
> > > {
> > > unsigned long flags;
> > >
> >
> > What's the code generation effect of this on say a defconfig kernel vmlinux with
> > paravirt enabled?
>
> Starting with this patch set applied:
> $ make CC=gcc-8 -j46
> $ objdump -d vmlinux | grep native_save_fl --context=3
> ffffffff81059140 <native_save_fl>:
> ffffffff81059140: 9c pushfq
> ffffffff81059141: 58 pop %rax
> ffffffff81059142: c3 retq
> $ git checkout HEAD~3
> $ make CC=gcc-8 -j46
> $ objdump -d vmlinux | grep native_save_fl --context=3
> ffffffff81079410 <native_save_fl>:
> ffffffff81079410: 9c pushfq
> ffffffff81079411: 58 pop %rax
> ffffffff81079412: c3 retq
>
> Mainly, this is to prevent the compiler from adding a stack protector
> to the outlined version, as the stack protector clobbers %rcx, but
> paravirt expects %rcx to be preserved. More info can be found:
> https://lkml.org/lkml/2018/5/24/1242--

Ok!

Acked-by: Ingo Molnar <mingo@kernel.org>

What's the planned upstreaming route for these patches/fixes?

Thanks,

Ingo