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Date: Sat, 30 Jul 2011 16:58:48 +0200
From: "Yann E. MORIN" <yann.morin.1998@...iens.enib.fr>
To: Radosław Smogura <mail@...gura.eu>
Cc: linux-kernel@...r.kernel.org, Michal Marek <mmarek@...e.cz>,
Randy Dunlap <rdunlap@...otime.net>,
linux-kbuild@...r.kernel.org
Subject: Re: [PATCH] Allows Kernel developer to change optimization options making code more debug friendly.
Radosław, all,
On Saturday 30 July 2011 14:33:54 Radosław Smogura wrote:
> New menu under kernel hacking allows to force "-01" optimization
> and gives ability to discard additional optimizations (passed
> with -O1). Options are added as "-f-no-..." to GCC invoke line.
> This make cause to produce additional warnings, but makes compiled
> code more debug friendly.
>
> Included new Makefile and new KConfig has been automaticly generated
> by simple bash script scripts/debug/make_config_optim.sh, which
> is included to simple add or remove new options.
For what they are worth, see my comments below.
Note: I'm not commenting the usefulness or not of such a change,
just suggesting readability changes.
[--SNIP--]
> diff --git a/Makefile b/Makefile
> index f676d15..1de2a79 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -558,12 +558,23 @@ endif # $(dot-config)
>
> # Defaults to vmlinux, but the arch makefile usually adds further targets
> all: vmlinux
>
> +ifdef CONFIG_HACK_OPTIM_FORCE_O1_LEVEL
> +KBUILD_CFLAGS += -O1
> +else
> +
>
> ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
> KBUILD_CFLAGS += -Os
> else
> KBUILD_CFLAGS += -O2
> endif
>
> +endif
endif # ! CONFIG_HACK_OPTIM_FORCE_O1_LEVEL
Thus, it's easier to spot the corresponding if/else.
> +# Include makefile for optimization override
> +ifdef CONFIG_HACK_OPTIM
> +include $(srctree)/scripts/Makefile.optim.inc
> +endif
> +
>
> include $(srctree)/arch/$(SRCARCH)/Makefile
>
> ifneq ($(CONFIG_FRAME_WARN),0)
[--SNIP--]
> diff --git a/scripts/debug/make_config_optim.sh b/scripts/debug/make_config_optim.sh
> new file mode 100644
> index 0000000..44736d7
> --- /dev/null
> +++ b/scripts/debug/make_config_optim.sh
> @@ -0,0 +1,92 @@
> +#!/bin/sh
> +
> +## Utility script for generating optimization override options
> +## for kernel compilation.
> +##
> +## Distributed under GPL v2 license
> +## (c) Radosław Smogura, 2011
> +
> +# Prefix added for variable
> +CFG_PREFIX="HACK_OPTIM"
> +
> +KCFG="Kconfig.debug.optim"
> +MKFI="Makefile.optim.inc"
> +OPTIMIZATIONS_PARAMS="-fno-inline-functions-called-once \
> + -fno-combine-stack-adjustments \
> + -fno-tree-dce \
> + -fno-tree-dominator-opts \
> + -fno-dse \
> + -fno-dce \
> + -fno-auto-inc-dec \
> + -fno-inline-small-functions \
> + -fno-if-conversion \
> + -fno-if-conversion2 \
> + -fno-tree-fre \
> + -fno-tree-dse \
> + -fno-tree-sra
> +"
> +
> +function printStandardHelp() {
> + echo -e "\t This changes how GCC optimizes code. Code" >> $KCFG
> + echo -e "\t may be slower and larger but will be more debug" >> $KCFG
> + echo -e "\t \"friendly\"." >> $KCFG
> + echo >> $KCFG
> + echo -e "\t In some cases there is a low chance that the kernel" >> $KCFG
> + echo -e "\t will run differently than normal, reporting or not" >> $KCFG
> + echo -e "\t reporting some bugs or errors." >> $KCFG
> + echo -e "\t Refer to GCC manual for more details." >> $KCFG
> + echo >> $KCFG
> + echo -e "\t You SHOULD say N here." >> $KCFG
> +}
To redirect output iun the function, but only when you call it:
printStandardHelp >>$KCFG
Don't use 'echo -e', its not protable. Prefer using printf:
printf "\t blabla\n"
In this case, you may even prefer using here-document:
cat <<_EOF_ >>"${KCFG}"
[TAB] blabla
[TAB] blabla
_EOF_
Also, enclose file names with double-quotes, it guards against future
changes where a file name would gain a space in it:
blabla >"$KCFG"
> +echo "# This file was auto generated. It's utility configuration" > $KCFG
> +echo "# Distributed under GPL v2 License" >> $KCFG
> +echo >> $KCFG
> +echo "menuconfig ${CFG_PREFIX}" >> $KCFG
With variables, use smthg like:
printf "menuconfig %s\n" "${CFG_PREFIX}"
Variables are expanded in here-documents:
cat <<_EOF_ >>"${KCFG}"
menuconfig ${CFG_PREFIX}
_EOF_
Also, be consistent in the way you /dereference/ variables. Either use one
the ${foo} or $foo, not both. Eg, you use $KCFG, but you use ${CFG_PREFIX}
I personnaly prefer ${foo} because it makes it explicit what the variable
name is.
> +echo -e "\tbool \"Allows overriding GCC optimizations\"" >> $KCFG
> +echo -e "\tdepends on DEBUG_KERNEL && EXPERIMENTAL" >> $KCFG
> +echo -e "\thelp" >> $KCFG
> +echo -e "\t If you say Y here you will be able to override" >> $KCFG
> +echo -e "\t how GCC optimizes kernel code. This creates" >> $KCFG
> +echo -e "\t more debug-friendly code, but does not guarantee" >> $KCFG
> +echo -e "\t the same running code like a production kernel." >> $KCFG
> +echo >> $KCFG
> +echo -e "\t If you say Y here probably you will want to say" >> $KCFG
> +echo -e "\t Y for all suboptions" >> $KCFG
> +echo >> $KCFG
> +echo "if ${CFG_PREFIX}" >> $KCFG
> +echo >> $KCFG
Make this a function that just sends to stdout, and call it with stdout
redirected to $KCFG :
printDotInHeader() {
cat <<_EOF_
[TAB]blabla
[TAB]help
[TAB] blabla
_EOF_
}
printDotInHeader >$KCFG
> +echo "# This file was auto generated. It's utility configuration" > $MKFI
> +echo "# Distributed under GPL v2 License" >> $MKFI
> +echo >> $MKFI
Ditto.
> +# Insert standard override optimization level
> +# This is exception, and this value will not be included
> +# in auto generated makefile. Support for this value
> +# is hard coded in main Makefile.
> +echo -e "config ${CFG_PREFIX}_FORCE_O1_LEVEL" >> $KCFG
> +echo -e "\tbool \"Forces -O1 optimization level\"" >> $KCFG
> +echo -e "\t---help---" >> $KCFG
> +printStandardHelp;
> +echo >> $KCFG
Ditto.
Also, it should be better to change the way 'CONFIG_CC_OPTIMIZE_FOR_SIZE'
works. For example:
choice
bool "Optimise level"
default CC_OPTIMIZE_O2
config CC_OPTIMIZE_O2
bool "O2, for speed"
config CC_OPTIMIZE_OS
bool "Os, for size"
config CC_OPTIMIZE_O1
bool "O1 (for debug only)"
endchoice
config CC_O_LEVEL
string
default "-O2" if CC_OPTIMIZE_O2
default "-Os" if CC_OPTIMIZE_Os
default "-O1" if CC_OPTIMIZE_O1
Then:
KBUILD_CFLAGS += "${CONFIG_CC_O_LEVEL}"
> +for o in $OPTIMIZATIONS_PARAMS ; do
> + cfg_o="${CFG_PREFIX}_${o//-/_}";
This is a bashism, and is not portable. If /bin/sh is not bash, this does
not work. Use sed:
cfg_o="$( printf "${o}" |sed -r -e 's/-/_/g;' )"
No need for a trailing ';'.
> + echo "Processing param ${o} config variable will be $cfg_o";
> +
> + # Generate kconfig entry
> + echo -e "config ${cfg_o}" >> $KCFG
> + echo -e "\tbool \"Adds $o parameter to gcc invoke line.\"" >> $KCFG
> + echo -e "\t---help---" >> $KCFG
'---help---' should be written as simply 'help'.
> + printStandardHelp;
> + echo >> $KCFG
Move this to a function (eg. printOption), with $1 being the name of the
option. Eg.:
printOption() {
cfg_o="$( printf "${o}" |sed -r -e 's/-/_/g;' )"
printf 'config %s%s\n' "${CFG_PREFIX" "${cfg_o}"
printf '\tbool "Adds %s prm to gcc\n' "${1}"
printf '\thelp\n'
printfStandardHelp
printf '\n'
}
for o in $OPTIMIZATIONS_PARAMS ; do
printOption "${o}" >>"${KCFG}"
printMakeVar "${o}" >> "${MKFI}"
done
> + #Generate Make for include
> + echo "ifdef CONFIG_${cfg_o}" >> $MKFI
> + echo -e "\tKBUILD_CFLAGS += $o" >> $MKFI
> + echo "endif" >> $MKFI
> + echo >> $MKFI
> +done;
> +echo "endif #${CFG_PREFIX}" >> $KCFG
>
Regards,
Yann E. MORIN.
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