linux-kernel - Re: [PATCH v2] lib/Kconfig.debug: introduce CONFIG_CC_STACK

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Date:	Sun, 13 Jul 2014 11:31:24 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Konstantin Khlebnikov <koct9i@...il.com>
Cc:	Michal Marek <mmarek@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org
Subject: Re: [PATCH v2] lib/Kconfig.debug: introduce CONFIG_CC_STACK_USAGE

Hi Konstantin.

On Sun, Jul 13, 2014 at 12:24:50AM +0400, Konstantin Khlebnikov wrote:
> This patch adds option for collecting stack usage statistics
> via gcc option '-fstack-usage' (needs gcc 4.6 or newer).
> For each .o file gcc dumps stack-frame sizes into .su file.
> 
> File format:
> <file>:<line>:<column>:<function>	<size>	<qualifiers>
> 
> select.c:870:5:do_sys_poll	1040	static
> rtnetlink.c:1880:12:rtnl_newlink        552     dynamic
> random.c:1334:1:random_read	664     dynamic,bounded
> 
> Quote from the gcc manpage about qualifiers:
> 
>     The qualifier "static" means that the function
>     manipulates the stack statically: a fixed number of bytes
>     are allocated for the frame on function entry and
>     released on function exit; no stack adjustments are
>     otherwise made in the function.  The second field is this
>     fixed number of bytes.
> 
>     The qualifier "dynamic" means that the function
>     manipulates the stack dynamically: in addition to the
>     static allocation described above, stack adjustments are
>     made in the body of the function, for example to push/pop
>     arguments around function calls.  If the qualifier
>     "bounded" is also present, the amount of these
>     adjustments is bounded at compile time and the second
>     field is an upper bound of the total amount of stack used
>     by the function.  If it is not present, the amount of
>     these adjustments is not bounded at compile time and the
>     second field only represents the bounded part.
> 
> In comparison to the scripts/checkstack.pl this method is more accurate.
> It takes into account function arguments, push/pop pairs, frame
> pointers and saved return address. It gives information about all
> functions except purely assember (for example sha1_transform_avx2).
> 
> Also this patch adds make target 'stack-usage' which combines all .su
> files into one sorted 'stack-usage'. Also prints top 100 and all unbounded
> dynamic stack frames.
> 
> Signed-off-by: Konstantin Khlebnikov <koct9i@...il.com>
> ---
>  .gitignore        |    3 +++
>  Makefile          |   23 ++++++++++++++++++++++-
>  lib/Kconfig.debug |    9 +++++++++
>  3 files changed, 34 insertions(+), 1 deletion(-)
> 
> diff --git a/.gitignore b/.gitignore
> index f4c0b09..96b8984 100644
> --- a/.gitignore
> +++ b/.gitignore
> @@ -85,6 +85,9 @@ GTAGS
>  *~
>  \#*#
>  
> +*.su
> +/stack-usage
> +
>  #
>  # Leavings from module signing
>  #
> diff --git a/Makefile b/Makefile
> index 2167084..29fe588 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -635,6 +635,11 @@ ifneq ($(CONFIG_FRAME_WARN),0)
>  KBUILD_CFLAGS += $(call cc-option,-Wframe-larger-than=${CONFIG_FRAME_WARN})
>  endif
>  
> +ifdef CONFIG_CC_STACK_USAGE
> +KBUILD_CFLAGS += $(call cc-option,-fstack-usage)
> +endif
> +CLEAN_FILES += stack-usage
> +
>  # Handle stack protector mode.
>  ifdef CONFIG_CC_STACKPROTECTOR_REGULAR
>    stackp-flag := -fstack-protector
> @@ -1228,6 +1233,7 @@ help:
>  	 echo  ''
>  	@echo  'Static analysers'
>  	@echo  '  checkstack      - Generate a list of stack hogs'
> +	@echo  '  stack-usage     - Alternative list of stack hogs'
>  	@echo  '  namespacecheck  - Name space analysis on compiled kernel'
>  	@echo  '  versioncheck    - Sanity check on version.h usage'
>  	@echo  '  includecheck    - Check for duplicate included header files'
The other "check" targets have check in their name.
Can we follow this naming convention and call it checkstackusage?


> @@ -1376,7 +1382,7 @@ clean: $(clean-dirs)
>  	$(call cmd,rmfiles)
>  	@find $(if $(KBUILD_EXTMOD), $(KBUILD_EXTMOD), .) $(RCS_FIND_IGNORE) \
>  		\( -name '*.[oas]' -o -name '*.ko' -o -name '.*.cmd' \
> -		-o -name '*.ko.*' \
> +		-o -name '*.ko.*' -o -name '*.su' \
>  		-o -name '.*.d' -o -name '.*.tmp' -o -name '*.mod.c' \
>  		-o -name '*.symtypes' -o -name 'modules.order' \
>  		-o -name modules.builtin -o -name '.tmp_*.o.*' \
> @@ -1432,6 +1438,21 @@ checkstack:
>  	$(OBJDUMP) -d vmlinux $$(find . -name '*.ko') | \
>  	$(PERL) $(src)/scripts/checkstack.pl $(CHECKSTACK_ARCH)
>  
> +quiet_cmd_cc_stack_usage = SORTING $@
> +cmd_cc_stack_usage = find -name '*.su' | xargs cat | sort -k 2 -n -r > $@
> +
> +stack-usage: FORCE
> +ifndef CONFIG_CC_STACK_USAGE
> +	$(Q)echo >&2 'Please rebuild with CONFIG_CC_STACK_USAGE=y' && false
> +endif
> +	$(call cmd,cc_stack_usage)
> +	$(Q)echo ''
> +	$(Q)echo 'Unbounded dynamic stack frames:'
> +	$(Q)grep '\bdynamic$$' $@ || true
> +	$(Q)echo ''
> +	$(Q)echo 'Top 100 stack frames:'
> +	$(Q)head -100 < $@
> +

All this belongs to a script - for example named

    scripts/checkstackusage.sh

The top-level Makefile shall be a thin driver and there are too much functionality
in that file. but this is no excuse for adding more.

	Sam
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