On Mon, Jul 02, 2018 at 12:04:07PM +0100, Mark Rutland wrote: > Now that all of the syscall logic works on the saved pt_regs, apply_ssbd > can safely corrupt x0-x3 in the entry paths, and we no longer need to > restore them. So let's remove the logic doing so. > > With that logic gone, we can fold the branch target into the macro, so > that callers need not deal with this. GAS provides \@, which provides a > unique value per macro invocation, which we can use to create a unique > label. > > Signed-off-by: Mark Rutland <mark.rutl...@arm.com> > Acked-by: Marc Zyngier <marc.zyng...@arm.com> > Acked-by: Catalin Marinas <catalin.mari...@arm.com> > Cc: Will Deacon <will.dea...@arm.com> > --- > arch/arm64/kernel/entry.S | 20 +++++++------------- > 1 file changed, 7 insertions(+), 13 deletions(-) > > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index c41b84d06644..728bc7cc5bbb 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -130,20 +130,21 @@ alternative_else_nop_endif > > // This macro corrupts x0-x3. It is the caller's duty > // to save/restore them if required. > - .macro apply_ssbd, state, targ, tmp1, tmp2 > + .macro apply_ssbd, state, tmp1, tmp2 > #ifdef CONFIG_ARM64_SSBD > alternative_cb arm64_enable_wa2_handling > - b \targ > + b skip_apply_ssbd\@ > alternative_cb_end > ldr_this_cpu \tmp2, arm64_ssbd_callback_required, \tmp1 > - cbz \tmp2, \targ > + cbz \tmp2, skip_apply_ssbd\@ > ldr \tmp2, [tsk, #TSK_TI_FLAGS] > - tbnz \tmp2, #TIF_SSBD, \targ > + tbnz \tmp2, #TIF_SSBD, skip_apply_ssbd\@
Talking to Dave, he makes a good point that this is pretty fragile if a macro expansion within the macro itself uses \@, since this would result in an unexpected label update and everything would go wrong. Can you default initialise an extra label argument to \@, or does that not work? Will
