Date:   Thu, 17 Aug 2017 00:03:05 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, Michal Marek <mmarek@...e.com>,
        X86 ML <x86@...nel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Douglas Anderson <dianders@...omium.org>,
        Michael Davidson <md@...gle.com>,
        Greg Hackmann <ghackmann@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Stephen Hines <srhines@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Arnd Bergmann <arnd@...db.de>,
        Bernhard Rosenkränzer 
        <Bernhard.Rosenkranzer@...aro.org>
Subject: Re: [PATCH v2 1/2] kbuild: Also evaluate alternative option passed to
 cc-option, etc

Hi Matthias,


2017-08-15 10:29 GMT+09:00 Matthias Kaehlcke <mka@...omium.org>:
> The macro cc-option receives two parameters (the second may be empty). It
> returns the first parameter if it is a valid compiler option, otherwise
> the second one. It is not evaluated if the second parameter is a valid
> compiler option. This seems to be fine in virtually all cases, however
> there are scenarios where the second parameter needs to be evaluated
> too, and an empty value (or a third option) should be returned if it is
> not valid.
>
> The new macro try-run-opt receives a 'base command' and two options as
> parameters. It runs 'base command' + option 1 and returns option 1
> upon success. In case of failure 'base command' + option 2 is executed,
> in case of success option 2 is returned, otherwise an empty string.
>
> Rework [__]cc-option, ld-option, and cc-ldoption to use try-run-opt
> instead of try-run to make sure the alternative option is evaluated.
>
> Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> ---
> Changes in v2:
> - add try-run-opt instead of cc-option-3
> - use try-run-opt for [__]cc-option, ld-option and ccld-option
> - updated subject (was 'kbuild: Add macros cc-option-3 and __cc-option-3')
>   and commit message
>
>  scripts/Kbuild.include | 33 +++++++++++++++++++++++++--------
>  1 file changed, 25 insertions(+), 8 deletions(-)
>
> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
> index dd8e2dde0b34..48a6d0e9b073 100644
> --- a/scripts/Kbuild.include
> +++ b/scripts/Kbuild.include
> @@ -85,8 +85,8 @@ TMPOUT := $(if $(KBUILD_EXTMOD),$(firstword $(KBUILD_EXTMOD))/)
>
>  # try-run
>  # Usage: option = $(call try-run, $(CC)...-o "$$TMP",option-ok,otherwise)
> -# Exit code chooses option. "$$TMP" is can be used as temporary file and
> -# is automatically cleaned up.
> +# Runs the command $1, exit code chooses option. "$$TMP" is used as temporary
> +# file and is automatically cleaned up.
>  try-run = $(shell set -e;              \
>         TMP="$(TMPOUT).$$$$.tmp";       \
>         TMPO="$(TMPOUT).$$$$.o";        \
> @@ -96,6 +96,23 @@ try-run = $(shell set -e;            \
>         fi;                             \
>         rm -f "$$TMP" "$$TMPO")
>
> +# try-run-opt
> +# Usage: option = $(call try-run-opt, $(CC)...-o "$$TMP",option-ok,otherwise)
> +# Runs the command '$1 $2' and outputs $2 if the execution was successful.
> +# Otherwise runs '$1 $3' (if $3 is not empty) and outputs $3 upon success. No
> +# output if both commands fail. "$$TMP" is used as temporary file and is
> +# automatically cleaned up.
> +try-run-opt = $(shell set -e;           \
> +        TMP="$(TMPOUT).$$$$.tmp";       \
> +        TMPO="$(TMPOUT).$$$$.o";        \
> +        if ($(1) $(2)) >/dev/null 2>&1; \
> +        then echo "$(2)";               \
> +        elif [ -n "$(3)" ] && ($(1) $(3)) >/dev/null 2>&1;      \
> +        then echo "$(3)";               \
> +        else echo "";                   \
> +        fi;                             \
> +        rm -f "$$TMP" "$$TMPO")
> +
>  # as-option
>  # Usage: cflags-y += $(call as-option,-Wa$(comma)-isa=foo,)
>
> @@ -110,8 +127,8 @@ as-instr = $(call try-run,\
>
>  # __cc-option
>  # Usage: MY_CFLAGS += $(call __cc-option,$(CC),$(MY_CFLAGS),-march=winchip-c6,-march=i586)
> -__cc-option = $(call try-run,\
> -       $(1) -Werror $(2) $(3) -c -x c /dev/null -o "$$TMP",$(3),$(4))
> +__cc-option = $(call try-run-opt,\
> +       $(1) -Werror $(2) -c -x c /dev/null -o "$$TMP",$(3),$(4))
>
>  # Do not attempt to build with gcc plugins during cc-option tests.
>  # (And this uses delayed resolution so the flags will be up to date.)
> @@ -159,13 +176,13 @@ cc-if-fullversion = $(shell [ $(cc-fullversion) $(1) $(2) ] && echo $(3) || echo
>
>  # cc-ldoption
>  # Usage: ldflags += $(call cc-ldoption, -Wl$(comma)--hash-style=both)
> -cc-ldoption = $(call try-run,\
> -       $(CC) $(1) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
> +cc-ldoption = $(call try-run-opt,\
> +       $(CC) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
>
>  # ld-option
>  # Usage: LDFLAGS += $(call ld-option, -X)
> -ld-option = $(call try-run,\
> -       $(CC) -x c /dev/null -c -o "$$TMPO" ; $(LD) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
> +ld-option = $(call try-run-opt,\
> +       $(CC) -x c /dev/null -c -o "$$TMPO" ; $(LD) "$$TMPO" -o "$$TMP",$(1),$(2))
>
>  # ar-option
>  # Usage: KBUILD_ARFLAGS := $(call ar-option,D)


Thanks for sending the patch,
but I am reluctant to add this to the common script
after consideration.  Sorry.

Currently, *-option and try-run are quite simple
and work for almost all cases.

The stack alignment option is one of rare scenarios, I think.
If we have more and more cases that need the second parameter evaluation,
we will need to support it in the common script somehow.

Otherwise, could you solve the problem in local Makefile?

(I was wondering if we can support multiple evaluation in a generic
try-run implementation,
for example using "for ... do ... done" loop of shell script,
but it would introduce much complexity.)



For example, one very ad-hoc solution:

# For gcc stack alignment is specified with -mpreferred-stack-boundary,
# clang has the option -mstack-alignment for that purpose.
ifneq ($(call cc-option, -mpreferred-stack-boundary=4),)
      cc_stack_align4 := -mpreferred-stack-boundary=2
      cc_stack_align8 := -mpreferred-stack-boundary=3
else
      cc_stack_align4 := -mstack-alignment=4
      cc_stack_align8 := -mstack-alignment=8
endif




-- 
Best Regards
Masahiro Yamada

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