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* [RESEND PATCH v2] bus: arm-cci: use asm unreachable
@ 2018-05-08 11:32 Stefan Agner
  2018-05-08 12:19 ` Robin Murphy
  0 siblings, 1 reply; 3+ messages in thread
From: Stefan Agner @ 2018-05-08 11:32 UTC (permalink / raw)
  To: arm, arnd
  Cc: linux, ard.biesheuvel, robin.murphy, nicolas.pitre, marc.zyngier,
	behanw, keescook, Bernhard.Rosenkranzer, mka, linux-arm-kernel,
	linux-kernel, Stefan Agner

Mixing asm and C code is not recommended in a naked function by
gcc and leads to an error when using clang:
  drivers/bus/arm-cci.c:2107:2: error: non-ASM statement in naked
  function is not supported
        unreachable();
        ^

While the function is marked __naked it actually properly return
in asm. There is no need for the unreachable() call.

Suggested-by: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Stefan Agner <stefan@agner.ch>
Acked-by: Nicolas Pitre <nico@linaro.org>
---
 drivers/bus/arm-cci.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/bus/arm-cci.c b/drivers/bus/arm-cci.c
index 443e4c3fd357..b8184a903583 100644
--- a/drivers/bus/arm-cci.c
+++ b/drivers/bus/arm-cci.c
@@ -371,8 +371,6 @@ asmlinkage void __naked cci_enable_port_for_self(void)
 	[sizeof_struct_cpu_port] "i" (sizeof(struct cpu_port)),
 	[sizeof_struct_ace_port] "i" (sizeof(struct cci_ace_port)),
 	[offsetof_port_phys] "i" (offsetof(struct cci_ace_port, phys)) );
-
-	unreachable();
 }
 
 /**
-- 
2.17.0

^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [RESEND PATCH v2] bus: arm-cci: use asm unreachable
  2018-05-08 11:32 [RESEND PATCH v2] bus: arm-cci: use asm unreachable Stefan Agner
@ 2018-05-08 12:19 ` Robin Murphy
  2018-05-08 13:01   ` Stefan Agner
  0 siblings, 1 reply; 3+ messages in thread
From: Robin Murphy @ 2018-05-08 12:19 UTC (permalink / raw)
  To: Stefan Agner, arm, arnd
  Cc: linux, ard.biesheuvel, nicolas.pitre, marc.zyngier, behanw,
	keescook, Bernhard.Rosenkranzer, mka, linux-arm-kernel,
	linux-kernel

On 08/05/18 12:32, Stefan Agner wrote:
> Mixing asm and C code is not recommended in a naked function by
> gcc and leads to an error when using clang:
>    drivers/bus/arm-cci.c:2107:2: error: non-ASM statement in naked
>    function is not supported
>          unreachable();
>          ^
> 
> While the function is marked __naked it actually properly return
> in asm. There is no need for the unreachable() call.

The commit title is a bit out-of-date now (I guess it could just be 
something like "remove unnecessary unreachable()" now), but the rest 
looks OK to me - even GCC clearly doesn't expect anything beyond the asm 
to be reachable anyway since the lack of epilogue includes the lack of 
any compiler-generated return. I've checked that GCC 7.2 generates 
identical object files before and after, other than (for obvious 
reasons) the line numbers generated by WANT_WARN_ON_SLOWPATH for all the 
WARN()s appearing later in the file.

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

> Suggested-by: Russell King <linux@arm.linux.org.uk>
> Signed-off-by: Stefan Agner <stefan@agner.ch>
> Acked-by: Nicolas Pitre <nico@linaro.org>
> ---
>   drivers/bus/arm-cci.c | 2 --
>   1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/bus/arm-cci.c b/drivers/bus/arm-cci.c
> index 443e4c3fd357..b8184a903583 100644
> --- a/drivers/bus/arm-cci.c
> +++ b/drivers/bus/arm-cci.c
> @@ -371,8 +371,6 @@ asmlinkage void __naked cci_enable_port_for_self(void)
>   	[sizeof_struct_cpu_port] "i" (sizeof(struct cpu_port)),
>   	[sizeof_struct_ace_port] "i" (sizeof(struct cci_ace_port)),
>   	[offsetof_port_phys] "i" (offsetof(struct cci_ace_port, phys)) );
> -
> -	unreachable();
>   }
>   
>   /**
> 

^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [RESEND PATCH v2] bus: arm-cci: use asm unreachable
  2018-05-08 12:19 ` Robin Murphy
@ 2018-05-08 13:01   ` Stefan Agner
  0 siblings, 0 replies; 3+ messages in thread
From: Stefan Agner @ 2018-05-08 13:01 UTC (permalink / raw)
  To: Robin Murphy
  Cc: arm, arnd, linux, ard.biesheuvel, nicolas.pitre, marc.zyngier,
	behanw, keescook, Bernhard.Rosenkranzer, mka, linux-arm-kernel,
	linux-kernel

On 08.05.2018 14:19, Robin Murphy wrote:
> On 08/05/18 12:32, Stefan Agner wrote:
>> Mixing asm and C code is not recommended in a naked function by
>> gcc and leads to an error when using clang:
>>    drivers/bus/arm-cci.c:2107:2: error: non-ASM statement in naked
>>    function is not supported
>>          unreachable();
>>          ^
>>
>> While the function is marked __naked it actually properly return
>> in asm. There is no need for the unreachable() call.
> 
> The commit title is a bit out-of-date now (I guess it could just be
> something like "remove unnecessary unreachable()" now), but the rest
> looks OK to me - even GCC clearly doesn't expect anything beyond the
> asm to be reachable anyway since the lack of epilogue includes the
> lack of any compiler-generated return. I've checked that GCC 7.2
> generates identical object files before and after, other than (for
> obvious reasons) the line numbers generated by WANT_WARN_ON_SLOWPATH
> for all the WARN()s appearing later in the file.

Title: Oops, good catch! Will send a v3.

Thanks for checking gcc.

--
Stefan

> 
> Reviewed-by: Robin Murphy <robin.murphy@arm.com>
> 
>> Suggested-by: Russell King <linux@arm.linux.org.uk>
>> Signed-off-by: Stefan Agner <stefan@agner.ch>
>> Acked-by: Nicolas Pitre <nico@linaro.org>
>> ---
>>   drivers/bus/arm-cci.c | 2 --
>>   1 file changed, 2 deletions(-)
>>
>> diff --git a/drivers/bus/arm-cci.c b/drivers/bus/arm-cci.c
>> index 443e4c3fd357..b8184a903583 100644
>> --- a/drivers/bus/arm-cci.c
>> +++ b/drivers/bus/arm-cci.c
>> @@ -371,8 +371,6 @@ asmlinkage void __naked cci_enable_port_for_self(void)
>>   	[sizeof_struct_cpu_port] "i" (sizeof(struct cpu_port)),
>>   	[sizeof_struct_ace_port] "i" (sizeof(struct cci_ace_port)),
>>   	[offsetof_port_phys] "i" (offsetof(struct cci_ace_port, phys)) );
>> -
>> -	unreachable();
>>   }
>>     /**
>>

^ permalink raw reply	[flat|nested] 3+ messages in thread

end of thread, other threads:[~2018-05-08 13:01 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2018-05-08 11:32 [RESEND PATCH v2] bus: arm-cci: use asm unreachable Stefan Agner
2018-05-08 12:19 ` Robin Murphy
2018-05-08 13:01   ` Stefan Agner

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