linux-kernel - Re: [RFC PATCH 01/11] Add basic support for gcc profiler instrumentation

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Date:	Thu, 3 Jan 2008 09:31:18 +0100
From:	Sam Ravnborg <sam@...nborg.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Hellwig <hch@...radead.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Gregory Haskins <ghaskins@...ell.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	"William L. Irwin" <sparclinux@...r.kernel.org>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [RFC PATCH 01/11] Add basic support for gcc profiler instrumentation

Hi Steven.

On Thu, Jan 03, 2008 at 02:16:10AM -0500, Steven Rostedt wrote:
> If CONFIG_MCOUNT is selected and /proc/sys/kernel/mcount_enabled is set to a
> non-zero value the mcount routine will be called everytime we enter a kernel
> function that is not marked with the "notrace" attribute.
> 
> The mcount routine will then call a registered function if a function
> happens to be registered.
> 
> [This code has been highly hacked by Steven Rostedt, so don't
>  blame Arnaldo for all of this ;-) ]
> 
> Signed-off-by: Arnaldo Carvalho de Melo <acme@...stprotocols.net>
> Signed-off-by: Steven Rostedt <srostedt@...hat.com>
> ---
> 
> Index: linux-compile.git/Documentation/stable_api_nonsense.txt
> ===================================================================
> --- linux-compile.git.orig/Documentation/stable_api_nonsense.txt	2008-01-03 01:02:28.000000000 -0500
> +++ linux-compile.git/Documentation/stable_api_nonsense.txt	2008-01-03 01:02:33.000000000 -0500
> @@ -62,6 +62,9 @@ consider the following facts about the L
>        - different structures can contain different fields
>        - Some functions may not be implemented at all, (i.e. some locks
>  	compile away to nothing for non-SMP builds.)
> +      - Parameter passing of variables from function to function can be
> +	done in different ways (the CONFIG_REGPARM option controls
> +	this.)

As CONFIG_REGPARM affects calling convention we should add it to the
list of symbols checked when loading modules (vermagic.h).


>        - Memory within the kernel can be aligned in different ways,
>  	depending on the build options.
>    - Linux runs on a wide range of different processor architectures.
> Index: linux-compile.git/Makefile
> ===================================================================
> --- linux-compile.git.orig/Makefile	2008-01-03 01:02:28.000000000 -0500
> +++ linux-compile.git/Makefile	2008-01-03 01:02:39.000000000 -0500
> @@ -509,11 +509,15 @@ endif
>  
>  include $(srctree)/arch/$(SRCARCH)/Makefile
>  
> +ifdef CONFIG_MCOUNT
> +KBUILD_CFLAGS	+= -pg -fno-omit-frame-pointer -fno-optimize-sibling-calls
> +else
>  ifdef CONFIG_FRAME_POINTER
>  KBUILD_CFLAGS	+= -fno-omit-frame-pointer -fno-optimize-sibling-calls
>  else
>  KBUILD_CFLAGS	+= -fomit-frame-pointer
>  endif
> +endif
Could we please move these relations to Kconfig. So we do not end up in a situation
where CONFIG_FRAME_POINTER is set but the flag is not added.



>  
>  ifdef CONFIG_DEBUG_INFO
>  KBUILD_CFLAGS	+= -g
> Index: linux-compile.git/arch/x86/Kconfig
> ===================================================================
> --- linux-compile.git.orig/arch/x86/Kconfig	2008-01-03 01:02:28.000000000 -0500
> +++ linux-compile.git/arch/x86/Kconfig	2008-01-03 01:02:33.000000000 -0500
> @@ -28,6 +28,12 @@ config GENERIC_CMOS_UPDATE
>  	bool
>  	default y
>  
> +# function tracing might turn this off:
> +config REGPARM
> +	bool
> +	depends on !MCOUNT
> +	default y
> +

Could we please define config REGPARM in _one_ Kconfig file
and let those who want it select it.
If you consider this x86 spacific this should be included in the naming
as in CONFIG_X86_REGPARM - and then the above is OK.

Defining the same config variable in several files is not good (but done too often these days).

> Index: linux-compile.git/lib/mcount/Makefile
> ===================================================================
> --- /dev/null	1970-01-01 00:00:00.000000000 +0000
> +++ linux-compile.git/lib/mcount/Makefile	2008-01-03 01:02:33.000000000 -0500
> @@ -0,0 +1,3 @@
> +obj-$(CONFIG_MCOUNT) += libmcount.o
> +
> +libmcount-objs := mcount.o

Preferred syntax is now:
libmcount-y := mcount.o

	Sam
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