[patch] x86, ptrace: void dopiness

[patch] x86, ptrace: void dopiness

[Markus Metzger]

Remove void cast to explicitly ignore the return value.


Signed-off-by: markus.t.metzger@intel.com

---
Index: gits.x86/arch/x86/kernel/ptrace.c
===================================================================
--- gits.x86.orig/arch/x86/kernel/ptrace.c	2008-06-30 13:21:07.%N +0200
+++ gits.x86/arch/x86/kernel/ptrace.c	2008-09-19 13:53:02.%N +0200
@@ -738,7 +738,7 @@
 		unsigned int sig = 0;
 
 		/* we ignore the error in case we were not tracing child */
-		(void)ds_release_bts(child);
+		ds_release_bts(child);
 
 		if (cfg.flags & PTRACE_BTS_O_SIGNAL) {
 			if (!cfg.signal)
@@ -947,7 +947,7 @@
 	clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
 #endif
 #ifdef CONFIG_X86_PTRACE_BTS
-	(void)ds_release_bts(child);
+	ds_release_bts(child);
 
 	child->thread.debugctlmsr &= ~bts_cfg.debugctl_mask;
 	if (!child->thread.debugctlmsr)
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Re: [patch] x86, ptrace: void dopiness

[linux-os (Dick Johnson)]

On Fri, 19 Sep 2008, Markus Metzger wrote:

> Remove void cast to explicitly ignore the return value.
>
>
> Signed-off-by: markus.t.metzger@intel.com
>
> ---
> Index: gits.x86/arch/x86/kernel/ptrace.c
> ===================================================================
> --- gits.x86.orig/arch/x86/kernel/ptrace.c	2008-06-30 13:21:07.%N +0200
> +++ gits.x86/arch/x86/kernel/ptrace.c	2008-09-19 13:53:02.%N +0200
> @@ -738,7 +738,7 @@
> 		unsigned int sig = 0;
>
> 		/* we ignore the error in case we were not tracing child */
> -		(void)ds_release_bts(child);
> +		ds_release_bts(child);
>
> 		if (cfg.flags & PTRACE_BTS_O_SIGNAL) {
> 			if (!cfg.signal)
> @@ -947,7 +947,7 @@
> 	clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
> #endif
> #ifdef CONFIG_X86_PTRACE_BTS
> -	(void)ds_release_bts(child);
> +	ds_release_bts(child);
>
> 	child->thread.debugctlmsr &= ~bts_cfg.debugctl_mask;
> 	if (!child->thread.debugctlmsr)
> ---------------------------------------------------------------------
> Intel GmbH
> Dornacher Strasse 1
> 85622 Feldkirchen/Muenchen Germany
> Sitz der Gesellschaft: Feldkirchen bei Muenchen
> Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer
> Registergericht: Muenchen HRB 47456 Ust.-IdNr.
> VAT Registration No.: DE129385895
> Citibank Frankfurt (BLZ 502 109 00) 600119052

I don't agree. Casting the return value to void, since it
takes extra steps on the part of the writer, means that the
writer is deliberately ignoring the return value because
it has no objective use in the code.

Just letting unused return-values be ignored means that
the writer either wanted to ignore it or simply forgot
about it. The cast is supposed to remove doubt. Certain
user-mode functions that are obviously used for effect
like printf(), are exempt.

That said, putting a space between the cast and the
function name helps in the use of some text-scanning
tools and therefore improves maintainability.


Cheers,
Dick Johnson
Penguin : Linux version 2.6.25.17 on an i686 machine (4786.70 BogoMips).
My book : http://www.AbominableFirebug.com/
_


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Thank you.

Re: [patch] x86, ptrace: void dopiness

[Ingo Molnar]

* Markus Metzger <markus.t.metzger@intel.com> wrote:

> +++ gits.x86/arch/x86/kernel/ptrace.c	2008-09-19 13:53:02.%N +0200
> @@ -738,7 +738,7 @@
>  		unsigned int sig = 0;
>  
>  		/* we ignore the error in case we were not tracing child */
> -		(void)ds_release_bts(child);
> +		ds_release_bts(child);

hm, here the cast is OK because we actually ignore the return value.

> @@ -947,7 +947,7 @@
>  	clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
>  #endif
>  #ifdef CONFIG_X86_PTRACE_BTS
> -	(void)ds_release_bts(child);
> +	ds_release_bts(child);

is it right/intentional here?

	Ingo

RE: [patch] x86, ptrace: void dopiness

[Metzger, Markus T]

>-----Original Message-----
>From: Ingo Molnar [mailto:mingo@elte.hu] 
>Sent: Montag, 22. September 2008 13:51
>To: Metzger, Markus T
>Cc: markus.t.metzger@gmail.com; linux-kernel@vger.kernel.org; 
>akpm@linux-foundation.org; Roland McGrath
>Subject: Re: [patch] x86, ptrace: void dopiness
>
>
>* Markus Metzger <markus.t.metzger@intel.com> wrote:
>
>> +++ gits.x86/arch/x86/kernel/ptrace.c	2008-09-19 
>13:53:02.%N +0200
>> @@ -738,7 +738,7 @@
>>  		unsigned int sig = 0;
>>  
>>  		/* we ignore the error in case we were not 
>tracing child */
>> -		(void)ds_release_bts(child);
>> +		ds_release_bts(child);
>
>hm, here the cast is OK because we actually ignore the return value.
>
>> @@ -947,7 +947,7 @@
>>  	clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
>>  #endif
>>  #ifdef CONFIG_X86_PTRACE_BTS
>> -	(void)ds_release_bts(child);
>> +	ds_release_bts(child);
>
>is it right/intentional here?

The void-cast is intentional in both cases.

I thought it a question of style, i.e. that we don't want void casts
just like we want NULL instead of 0.

regards,
markus.

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Re: [patch] x86, ptrace: void dopiness

[Ingo Molnar]

* Metzger, Markus T <markus.t.metzger@intel.com> wrote:

> >-----Original Message-----
> >From: Ingo Molnar [mailto:mingo@elte.hu] 
> >Sent: Montag, 22. September 2008 13:51
> >To: Metzger, Markus T
> >Cc: markus.t.metzger@gmail.com; linux-kernel@vger.kernel.org; 
> >akpm@linux-foundation.org; Roland McGrath
> >Subject: Re: [patch] x86, ptrace: void dopiness
> >
> >
> >* Markus Metzger <markus.t.metzger@intel.com> wrote:
> >
> >> +++ gits.x86/arch/x86/kernel/ptrace.c	2008-09-19 
> >13:53:02.%N +0200
> >> @@ -738,7 +738,7 @@
> >>  		unsigned int sig = 0;
> >>  
> >>  		/* we ignore the error in case we were not 
> >tracing child */
> >> -		(void)ds_release_bts(child);
> >> +		ds_release_bts(child);
> >
> >hm, here the cast is OK because we actually ignore the return value.
> >
> >> @@ -947,7 +947,7 @@
> >>  	clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
> >>  #endif
> >>  #ifdef CONFIG_X86_PTRACE_BTS
> >> -	(void)ds_release_bts(child);
> >> +	ds_release_bts(child);
> >
> >is it right/intentional here?
> 
> The void-cast is intentional in both cases.
> 
> I thought it a question of style, i.e. that we don't want void casts 
> just like we want NULL instead of 0.

ok.

But you could mark ds_release_bts() as a __must_check function, in that 
case the (void) has functional aspects as well: the kernel build will 
complain if a return value is ignored unintentionally.

So i think the code might be fine as-is after all :-/

	Ingo

RE: [patch] x86, ptrace: void dopiness

[Metzger, Markus T]

>-----Original Message-----
>From: Ingo Molnar [mailto:mingo@elte.hu] 
>Sent: Montag, 22. September 2008 14:08
>To: Metzger, Markus T

>> The void-cast is intentional in both cases.
>> 
>> I thought it a question of style, i.e. that we don't want void casts 
>> just like we want NULL instead of 0.
>
>ok.
>
>But you could mark ds_release_bts() as a __must_check 
>function, in that 
>case the (void) has functional aspects as well: the kernel build will 
>complain if a return value is ignored unintentionally.

Wouldn't every non-void function be __must_check?

regards,
markus.
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Re: [patch] x86, ptrace: void dopiness

[Ingo Molnar]

* Metzger, Markus T <markus.t.metzger@intel.com> wrote:

> >-----Original Message-----
> >From: Ingo Molnar [mailto:mingo@elte.hu] 
> >Sent: Montag, 22. September 2008 14:08
> >To: Metzger, Markus T
> 
> >> The void-cast is intentional in both cases.
> >> 
> >> I thought it a question of style, i.e. that we don't want void casts 
> >> just like we want NULL instead of 0.
> >
> >ok.
> >
> >But you could mark ds_release_bts() as a __must_check 
> >function, in that 
> >case the (void) has functional aspects as well: the kernel build will 
> >complain if a return value is ignored unintentionally.
> 
> Wouldn't every non-void function be __must_check?

no, only those which we mark so explicitly.

	Ingo