linux-kernel - Re: [tip:perf/uprobes] uprobes/core: Clean up, refactor and improve the code

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Date:	Mon, 20 Feb 2012 11:38:25 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	jkenisto@...ibm.com, a.p.zijlstra@...llo.nl, ananth@...ibm.com,
	anton@...hat.com, masami.hiramatsu.pt@...achi.com,
	acme@...radead.org, oleg@...hat.com, tglx@...utronix.de,
	mingo@...e.hu, Benjamin Herrenschmidt <benh@....ibm.com>,
	Josh Stone <jistone@...hat.com>
Cc:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/uprobes] uprobes/core: Clean up,  refactor and
 improve the code

> 
>  - remove unnecessary volatile

volatiles were added because of warnings thrown by gcc-4.6. Please see
below.

> 
>  - restructure comment blocks to make them more uniform and
>    more readable in general
> 

...

> diff --git a/arch/Kconfig b/arch/Kconfig
> index 284f589..cca5b54 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -66,13 +66,19 @@ config OPTPROBES
>  	depends on !PREEMPT
> 
>  config UPROBES
> -	bool "User-space probes (EXPERIMENTAL)"
> +	bool "Transparent user-space probes (EXPERIMENTAL)"
>  	depends on ARCH_SUPPORTS_UPROBES
>  	default n
>  	help
> -	  Uprobes enables kernel subsystems to establish probepoints
> -	  in user applications and execute handler functions when
> -	  the probepoints are hit.
> +	  Uprobes is the user-space counterpart to kprobes: they
> +	  enable instrumentation applications (such as 'perf probe')
> +	  to establish unintrusive probes in user-space binaries and
> +	  libraries, by executing handler functions when the probes
> +	  are hit by user-space applications.
> +
> +	  ( These probes come in the form of single-byte breakpoints,

One nit: In some architectures like powerpc, the breakpoints arent
single-byte.

> +	    managed by the kernel and kept transparent to the probed
> +	    application. )
> 
>  	  If in doubt, say "N".
> 
> 
>  #ifdef CONFIG_X86_64
> -static volatile u32 good_insns_64[256 / 32] = {
> +static u32 good_insns_64[256 / 32] = {

The volatiles were added to arch/x86/kernel/kprobes.c because of commit
7115e3fcf45 and 315eb8a2a1b. The volatiles are required because gcc 4.6
gave a warning about the asm operand for test_bit.  So the same were
added to arch/x86/kernel/uprobes.c.

-- 
Thanks and Regards
Srikar

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