[PATCH] lib/Kconfig.debug: introduce CONFIG_CC_STACK_USAGE

From: Konstantin Khlebnikov
Date: Sat Jul 12 2014 - 16:01:53 EST

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@xxxxxxxxx>
Makefile | 22 +++++++++++++++++++++-
lib/Kconfig.debug | 9 +++++++++
2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 2167084..9ba61ee 100644
--- a/Makefile
+++ b/Makefile
@@ -635,6 +635,10 @@ ifneq ($(CONFIG_FRAME_WARN),0)
KBUILD_CFLAGS += $(call cc-option,-Wframe-larger-than=${CONFIG_FRAME_WARN})

+KBUILD_CFLAGS += $(call cc-option,-fstack-usage)
# Handle stack protector mode.
stackp-flag := -fstack-protector
@@ -1228,6 +1232,7 @@ 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'
@@ -1376,7 +1381,7 @@ clean: $(clean-dirs)
$(call cmd,rmfiles)
\( -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 +1437,21 @@ 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
+ $(Q)echo >&2 'Please rebuild with CONFIG_CC_STACK_USAGE=y' && false
+ $(call cmd,cc_stack_usage)
+ $(Q)echo ''
+ $(Q)echo 'Unbounded dynamic stack frames:'
+ $(Q)grep '\bdynamic$$' $@
+ $(Q)echo ''
+ $(Q)echo 'Top 100 stack frames:'
+ $(Q)head -100 < $@
@echo "$(KERNELVERSION)$$($(CONFIG_SHELL) $(srctree)/scripts/setlocalversion $(srctree))"

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 7a638aa..3b30853 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -170,6 +170,15 @@ config FRAME_WARN
Setting it to 0 disables the warning.
Requires gcc 4.4

+ bool "Collect statistics about stack usage (needs gcc 4.6)"
+ help
+ This enables gcc option -fstack-usage which saves information
+ about stack frames in per-function basis into '.su' files.
+ Run 'make stack-usage' after building kernel and modules to
+ combine all information in one file.
bool "Strip assembler-generated symbols during link"
default n

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