Re: [PATCH v3 1/5] build: make cc-option properly deal with unrecognized sub-options

[Jan Beulich <jbeulich@xxxxxxxx>]

On 11.08.2023 15:48, Anthony PERARD wrote:
> On Wed, Jul 26, 2023 at 12:33:07PM +0200, Jan Beulich wrote:
>> In options like -march=, it may be only the sub-option which is
>> unrecognized by the compiler. In such an event the error message often
>> splits option and argument, typically saying something like "bad value
>> '<argument>' for '<option>'. Extend the grep invocation accordingly,
>> also accounting for Clang to not mention e.g. -march at all when an
>> incorrect argument was given for it.
>>
>> To keep things halfway readable, re-wrap and re-indent the entire
>> construct.
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> ---
>> In principle -e "$$pat" could now be omitted from the grep invocation,
>> since if that matches, both $$opt and $$arg will, too. But I thought I'd
>> leave it for completeness.
>> ---
>> v3: Fix build with make 4.3 and newer, where the treatment of \# has
>>     changed.
>> v2: Further relax grep patterns for clang, which doesn't mention -march
>>     when complaining about an invalid argument to it.
>>
>> --- a/Config.mk
>> +++ b/Config.mk
>> @@ -8,6 +8,7 @@ endif
>>  comma   := ,
>>  open    := (
>>  close   := )
>> +sharp   := \#
>>  squote  := '
>>  #' Balancing squote, to help syntax highlighting
>>  empty   :=
>> @@ -90,9 +91,14 @@ PYTHON_PREFIX_ARG ?= --prefix="$(prefix)
>>  # of which would indicate an "unrecognized command-line option" 
>> warning/error.
>>  #
>>  # Usage: cflags-y += $(call cc-option,$(CC),-march=winchip-c6,-march=i586)
>> -cc-option = $(shell if test -z "`echo 'void*p=1;' | \
>> -              $(1) $(2) -c -o /dev/null -x c - 2>&1 | grep -- 
>> $(2:-Wa$(comma)%=%) -`"; \
>> -              then echo "$(2)"; else echo "$(3)"; fi ;)
>> +cc-option = $(shell pat='$(2:-Wa$(comma)%=%)'; \
>> +                    opt="$${pat%%=*}" arg="$${pat$(sharp)*=}"; \
>> +                    if test -z "`echo 'void*p=1;' | \
>> +                                 $(1) $(2) -c -o /dev/null -x c - 2>&1 | \
>> +                                 grep -e "$$pat" -e "$$opt" -e "$$arg" -`"; 
>> \
>> +                    then echo "$(2)"; \
>> +                    else echo "$(3)"; \
>> +                    fi;)
> 
> This patch looks fine. Shouldn't the comment been updated as well? At
> the moment, it only discuss about -Wno-*, which it seems is why `grep`
> was introduced in the first place.

Right, but that has been an issue already before.

> But isn't it doing doing pattern matching on an error message going to
> lead sometime to false positive?

There's a certain risk, of course.

> Linux's build system seems to works
> fine by just using the exit value. They've got a few trick to deal with
> -Wno-* and with clang.
> 
> For -Wno-$(warning), they test -W$(warning) instead. For clang, they've
> enable additional warnings:
>     -Werror=unknown-warning-option
>     -Werror=ignored-optimization-argument
>     -Werror=option-ignored
>     -Werror=unused-command-line-argument

Ah, yes, this would likely be a better way to test things. Time to redo
what was done 12 years ago. I guess for the purpose of this series I'll
keep what I have, but take note to rework things afterwards (which now
would likely mean post-4.18, as the new-submissions deadline has passed).

> In any case, the patch is fine.
> Reviewed-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>

Thanks.

Jan