linux-kernel - Re: [PATCH] arm64: annotate psci invoke functions as notrace

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Date:	Sun, 19 Apr 2015 08:40:26 -0300
From:	Vinicius Tinti <viniciustinti@...il.com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	"Richard W.M. Jones" <rjones@...hat.com>,
	Will Deacon <Will.Deacon@....com>,
	Kyle McMartin <kyle@...hat.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm64: annotate psci invoke functions as notrace

On Tue, Feb 24, 2015 at 3:11 PM, Mark Rutland <mark.rutland@....com> wrote:
> On Tue, Feb 24, 2015 at 05:59:50PM +0000, Richard W.M. Jones wrote:
>> On Wed, Feb 18, 2015 at 12:26:38PM -0500, Kyle McMartin wrote:
>> > Using GCC 5 to build the kernel with ftrace enabled, we encounter the
>> > following error as a result of the mcount prologue changing the expected
>> > register use of the function parameters,
>> >
>> > /tmp/cc8Kpn7A.s: Assembler messages:
>> > /tmp/cc8Kpn7A.s:41: Error: .err encountered
>> > /tmp/cc8Kpn7A.s:42: Error: .err encountered
>> > /tmp/cc8Kpn7A.s:43: Error: .err encountered
>> > /tmp/cc8Kpn7A.s:101: Error: .err encountered
>> > /tmp/cc8Kpn7A.s:102: Error: .err encountered
>> > /tmp/cc8Kpn7A.s:103: Error: .err encountered
>> > scripts/Makefile.build:257: recipe for target 'arch/arm64/kernel/psci.o' failed
>> >
>> > Fix this by annotating the function as notrace, to suppress the
>> > generation of profiling prologues and epilogues on the function.
>> >
>> > Signed-off-by: Kyle McMartin <kyle@...hat.com>
>> >
>> > --- a/arch/arm64/kernel/psci.c
>> > +++ b/arch/arm64/kernel/psci.c
>> > @@ -113,7 +113,7 @@ static void psci_power_state_unpack(u32 power_state,
>> >   * The following two functions are invoked via the invoke_psci_fn pointer
>> >   * and will not be inlined, allowing us to piggyback on the AAPCS.
>> >   */
>> > -static noinline int __invoke_psci_fn_hvc(u64 function_id, u64 arg0, u64 arg1,
>> > +static noinline notrace int __invoke_psci_fn_hvc(u64 function_id, u64 arg0, u64 arg1,
>> >                                      u64 arg2)
>> >  {
>> >     asm volatile(
>> > @@ -128,7 +128,7 @@ static noinline int __invoke_psci_fn_hvc(u64 function_id, u64 arg0, u64 arg1,
>> >     return function_id;
>> >  }
>> >
>> > -static noinline int __invoke_psci_fn_smc(u64 function_id, u64 arg0, u64 arg1,
>> > +static noinline notrace int __invoke_psci_fn_smc(u64 function_id, u64 arg0, u64 arg1,
>> >                                      u64 arg2)
>> >  {
>> >     asm volatile(
>>
>> I need this patch in order to compile the upstream kernel on aarch64
>> using gcc 5.  Can it not be added temporarily while the longer term
>> fix, whatever that is, is worked out?
>
> As I mentioned in my reply, Will was waiting for -rc1 to post our
> patches (which move this out to asm for arm and arm64). He's out of the
> office today, but I expect they will be posted tomorrow (and hopefully
> queued shortly thereafter).
>
> Mark.
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Hi,

I notice that the mainline kernel moved these psci calls to a separate
file but I
was wondering how can it guarantee that the function register
placement will hold?

If you build the kernel with -O0 some function register allocation changes as
opposed to -O2 or if you use another compiler such as Clang. In LLVMLinux we
solved this by using one of Andy's solution which is to use register placement:

  register u32 function_id_r0 asm ("r0") = function_id;
  register u32 arg0_r1 asm ("r1") = arg0;
  register u32 arg1_r2 asm ("r2") = arg1;
  register u32 arg2_r3 asm ("r3") = arg2;

Sorry by the late reply.

Regards,
Tinti

-- 
Simplicity is the ultimate sophistication
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