Re: [PATCH 0.5/3] build: make cc-option properly deal with unrecognized sub-options

From: Jan Beulich <jbeulich@suse.com>
To: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: "Roger Pau Monné" <roger.pau@citrix.com>,
	"Anthony Perard" <anthony.perard@citrix.com>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"George Dunlap" <george.dunlap@citrix.com>,
	"Julien Grall" <julien@xen.org>,
	"Stefano Stabellini" <sstabellini@kernel.org>,
	"Wei Liu" <wl@xen.org>
Subject: Re: [PATCH 0.5/3] build: make cc-option properly deal with unrecognized sub-options
Date: Tue, 18 Jul 2023 16:09:19 +0200	[thread overview]
Message-ID: <7ba24ac4-1f20-906c-8e38-6a8b040af35a@suse.com> (raw)
In-Reply-To: <fe4c01c0-91cd-a303-71e9-96a81e46ddff@suse.com>

On 12.07.2023 16:26, Jan Beulich wrote:
> --- a/Config.mk
> +++ b/Config.mk
> @@ -90,9 +90,14 @@ 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\#*=}"; \
> +                    if test -z "`echo 'void*p=1;' | \
> +                                 $(1) $(2) -c -o /dev/null -x c - 2>&1 | \
> +                                 grep -e "$$pat" -e "$$arg.*$$opt" -e "$$opt.*$$arg" -`"; \

Sigh. At least some versions of Clang (I'm looking at 7.0.1 right now)
don't quote "-march" in their resulting error message. So I guess all
we can do (without finding a different approach to the checking
altogether) is further relax the grep pattern, to

grep -e "$$pat" -e "$$opt" -e "$$arg" -

Of course this has the increasing risk of getting false positives (i.e.
false negatives for the overall check result).

Jan