Re: [PATCH v2 3/6] ARM: trusted_foundations: do not use naked function

[Stephen Warren]

On 04/16/2018 09:56 AM, Stefan Agner wrote:
> On 27.03.2018 14:16, Dmitry Osipenko wrote:
> > On 27.03.2018 14:54, Robin Murphy wrote:
> > > On 26/03/18 22:20, Dmitry Osipenko wrote:
> > > > On 25.03.2018 21:09, Stefan Agner wrote:
> > > > > As documented in GCC naked functions should only use Basic asm
> > > > > syntax. The Extended asm or mixture of Basic asm and "C" code is
> > > > > not guaranteed. Currently this works because it was hard coded
> > > > > to follow and check GCC behavior for arguments and register
> > > > > placement.
> > > > >
> > > > > Furthermore with clang using parameters in Extended asm in a
> > > > > naked function is not supported:
> > > > >  ÂÂ arch/arm/firmware/trusted_foundations.c:47:10: error: parameter
> > > > >  ÂÂÂÂÂÂÂÂÂÂ references not allowed in naked functions
> > > > >  ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ : "r" (type), "r" (arg1), "r" (arg2)
> > > > >  ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ ^
> > > > >
> > > > > Use a regular function to be more portable. This aligns also with
> > > > > the other smc call implementations e.g. in qcom_scm-32.c and
> > > > > bcm_kona_smc.c.
> > > > >
> > > > > Cc: Dmitry Osipenko <digetx@xxxxxxxxx>
> > > > > Cc: Stephen Warren <swarren@xxxxxxxxxx>
> > > > > Cc: Thierry Reding <treding@xxxxxxxxxx>
> > > > > Signed-off-by: Stefan Agner <stefan@xxxxxxxx>
> > > > > ---
> > > > > Changes in v2:
> > > > > - Keep stmfd/ldmfd to avoid potential ABI issues
> > > > >
> > > > >  Â arch/arm/firmware/trusted_foundations.c | 14 +++++++++-----
> > > > >  Â 1 file changed, 9 insertions(+), 5 deletions(-)
> > > > >
> > > > > diff --git a/arch/arm/firmware/trusted_foundations.c
> > > > > b/arch/arm/firmware/trusted_foundations.c
> > > > > index 3fb1b5a1dce9..689e6565abfc 100644
> > > > > --- a/arch/arm/firmware/trusted_foundations.c
> > > > > +++ b/arch/arm/firmware/trusted_foundations.c
> > > > > @@ -31,21 +31,25 @@
> > > > >  Â Â static unsigned long cpu_boot_addr;
> > > > >  Â -static void __naked tf_generic_smc(u32 type, u32 arg1, u32 arg2)
> > > > > +static void tf_generic_smc(u32 type, u32 arg1, u32 arg2)
> > > > >  Â {
> > > > > +ÂÂÂ register u32 r0 asm("r0") = type;
> > > > > +ÂÂÂ register u32 r1 asm("r1") = arg1;
> > > > > +ÂÂÂ register u32 r2 asm("r2") = arg2;
> > > > > +
> > > > >  ÂÂÂÂÂ asm volatile(
> > > > >  ÂÂÂÂÂÂÂÂÂ ".arch_extensionÂÂÂ sec\n\t"
> > > > > -ÂÂÂÂÂÂÂ "stmfdÂÂÂ sp!, {r4 - r11, lr}\n\t"
> > > > > +ÂÂÂÂÂÂÂ "stmfdÂÂÂ sp!, {r4 - r11}\n\t"
> > > > >  ÂÂÂÂÂÂÂÂÂ __asmeq("%0", "r0")
> > > > >  ÂÂÂÂÂÂÂÂÂ __asmeq("%1", "r1")
> > > > >  ÂÂÂÂÂÂÂÂÂ __asmeq("%2", "r2")
> > > > >  ÂÂÂÂÂÂÂÂÂ "movÂÂÂ r3, #0\n\t"
> > > > >  ÂÂÂÂÂÂÂÂÂ "movÂÂÂ r4, #0\n\t"
> > > > >  ÂÂÂÂÂÂÂÂÂ "smcÂÂÂ #0\n\t"
> > > > > -ÂÂÂÂÂÂÂ "ldmfdÂÂÂ sp!, {r4 - r11, pc}"
> > > > > +ÂÂÂÂÂÂÂ "ldmfdÂÂÂ sp!, {r4 - r11}\n\t"
> > > > >  ÂÂÂÂÂÂÂÂÂ :
> > > > > -ÂÂÂÂÂÂÂ : "r" (type), "r" (arg1), "r" (arg2)
> > > > > -ÂÂÂÂÂÂÂ : "memory");
> > > > > +ÂÂÂÂÂÂÂ : "r" (r0), "r" (r1), "r" (r2)
> > > > > +ÂÂÂÂÂÂÂ : "memory", "r3", "r12", "lr");
> > > >
> > > > Although seems "lr" won't be affected by SMC invocation because it should be
> > > > banked and hence could be omitted entirely from the code. Maybe somebody could
> > > > confirm this.
> > > Strictly per the letter of the architecture, the SMC could be trapped to Hyp
> > > mode, and a hypervisor might clobber LR_usr in the process of forwarding the
> > > call to the firmware secure monitor (since Hyp doesn't have a banked LR of its
> > > own). Admittedly there are probably no real systems with the appropriate
> > > hardware/software combination to hit that, but on the other hand if this gets
> > > inlined where the compiler has already created a stack frame then an LR clobber
> > > is essentially free, so I reckon we're better off keeping it for reassurance.
> > > This isn't exactly a critical fast path anyway.
> >
> > Okay, thank you for the clarification.
>
> So it seems this change is fine?
>
> Stephen, you picked up changes for this driver before, is this patch
> going through your tree?

You had best ask Thierry; he's taken over Tegra maintenance upstream. 
But that said, don't files in arch/arm go through Russell?