linux-kernel - Re: [RFC PATCH 3/4] gcov: compile specific gcov implementation based on gcc version

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Message-ID: <20130824191227.GA2365@localhost.localdomain>
Date:	Sat, 24 Aug 2013 21:12:27 +0200
From:	Frantisek Hrbata <fhrbata@...hat.com>
To:	Peter Oberparleiter <oberpar@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, jstancek@...hat.com,
	keescook@...omium.org, rusty@...tcorp.com.au,
	linux-arch@...r.kernel.org, arnd@...db.de, mgahagan@...hat.com,
	agospoda@...hat.com
Subject: Re: [RFC PATCH 3/4] gcov: compile specific gcov implementation based
 on gcc version

On Fri, Aug 23, 2013 at 05:15:19PM +0200, Peter Oberparleiter wrote:
> On 23.08.2013 10:39, Frantisek Hrbata wrote:
> > Compile the correct gcov implementation file for a specific gcc version. In
> > the future, if another file is added, the conditions will need to be somehow
> > adjusted to if-elif-else case, but at this point the simple cc-ifversion should
> > be enough.
> 
> Looks good, though I think this could be merged into the main 4.7 format patch,
> since without it, the 4.7 code will never be reached.

Sure, I can merge these two patches.

> 
> Also it is my understanding that there are some distribution-specific versions
> of GCC that include the 4.7. gcov format code but report GCC version 4.6. With
> the auto-detection code implemented like this, gcov-kernel won't work correctly.
> For that purpose I've implemented a configuration option to allow users to
> force a specific version of gcov format.

Ah, I was not aware of this inconsistency in versioning. This raises a question
if it would not be better to deal directly with version in the gcov_info
instead of these config options. This would of course mean some kind of gcov
operations callbacks per gcov version(you already mentioned the file
operations approach).

> 
> I'm attaching the corresponding patch below:
> 
> ---
> kernel: gcov: make data format configurable
> 
> Make the format of the generated gcov data configurable. This may be
> required for example for pre-4.7 GCCs that contain the 4.7 gcov data
> format changes.
> 
> Signed-off-by: Peter Oberparleiter <oberpar@...ux.vnet.ibm.com>
> ---
>  kernel/gcov/Kconfig  |   30 ++++++++++++++++++++++++++++++
>  kernel/gcov/Makefile |   21 +++++++++++++++++++--
>  2 files changed, 49 insertions(+), 2 deletions(-)
> 
> --- a/kernel/gcov/Kconfig
> +++ b/kernel/gcov/Kconfig
> @@ -46,4 +46,34 @@ config GCOV_PROFILE_ALL
>  	larger and run slower. Also be sure to exclude files from profiling
>  	which are not linked to the kernel image to prevent linker errors.
> 
> +choice
> +	prompt "Specify GCOV format"
> +	depends on GCOV_KERNEL
> +	default GCOV_FORMAT_AUTODETECT
> +	---help---
> +	The gcov format is usually determined by the GCC version, but there are
> +	exceptions where format changes are integrated in lower-version GCCs.
> +	In such a case use this option to adjust the format used in the kernel
> +	accordingly.
> +
> +	If unsure, choose "Autodetect".
> +
> +config GCOV_FORMAT_AUTODETECT
> +	bool "Autodetect"
> +	---help---
> +	Select this option to use the format that corresponds to your GCC
> +	version.
> +
> +config GCOV_FORMAT_3_4
> +	bool "GCC 3.4 format"
> +	---help---
> +	Select this option to use the format defined by GCC 3.4.
> +
> +config GCOV_FORMAT_4_7
> +	bool "GCC 4.7 format"
> +	---help---
> +	Select this option to use the format defined by GCC 4.7.
> +
> +endchoice
> +
>  endmenu
> --- a/kernel/gcov/Makefile
> +++ b/kernel/gcov/Makefile
> @@ -1,5 +1,22 @@
>  ccflags-y := -DSRCTREE='"$(srctree)"' -DOBJTREE='"$(objtree)"'
> 
> +# if-lt
> +# Usage VAR := $(call if-lt, $(a), $(b))
> +# Returns 1 if (a < b)
> +if-lt = $(shell [ $(1) -lt $(2) ] && echo 1)
> +
> +ifeq ($(CONFIG_GCOV_FORMAT_3_4),y)
> +  cc-ver := 0304
> +else ifeq ($(CONFIG_GCOV_FORMAT_4_7),y)
> +  cc-ver := 0407
> +else
> +  cc-ver := $(call cc-version)
> +endif
> +
>  obj-$(CONFIG_GCOV_KERNEL) := base.o fs.o
> -obj-$(CONFIG_GCOV_KERNEL) += $(call cc-ifversion, -lt, 0407, gcc_3_4.o)
> -obj-$(CONFIG_GCOV_KERNEL) += $(call cc-ifversion, -ge, 0407, gcc_4_7.o)
> +
> +ifeq ($(call if-lt, $(cc-ver), 0407),1)
> +  obj-$(CONFIG_GCOV_KERNEL) += gcc_3_4.o
> +else
> +  obj-$(CONFIG_GCOV_KERNEL) += gcc_4_7.o
> +endif
> 
> 
> -- 
> Peter Oberparleiter
> Linux on System z Development - IBM Germany
> 

-- 
Frantisek Hrbata
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