Re: [kvm-unit-tests PATCH 3/3] Makefile: use "-Werror" in cc-option

[Thomas Huth <thuth@redhat.com>]

On 10/10/2019 20.35, Bill Wendling wrote:
> The "cc-option" macro should use "-Werror" to determine if a flag is
> supported. Otherwise the test may not return a nonzero result. Also
> conditionalize some of the warning flags which aren't supported by
> clang.
> 
> Signed-off-by: Bill Wendling <morbo@google.com>
> ---
>  Makefile | 19 +++++++++++--------
>  1 file changed, 11 insertions(+), 8 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index 32414dc..3ec0458 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -46,30 +46,33 @@ include $(SRCDIR)/$(TEST_DIR)/Makefile
>  # cc-option
>  # Usage: OP_CFLAGS+=$(call cc-option, -falign-functions=0, -malign-functions=0)
>  
> -cc-option = $(shell if $(CC) $(1) -S -o /dev/null -xc /dev/null \
> +cc-option = $(shell if $(CC) -Werror $(1) -S -o /dev/null -xc /dev/null \
>                > /dev/null 2>&1; then echo "$(1)"; else echo "$(2)"; fi ;)
>  
>  COMMON_CFLAGS += -g $(autodepend-flags)
> -COMMON_CFLAGS += -Wall -Wwrite-strings -Wclobbered -Wempty-body -Wuninitialized
> -COMMON_CFLAGS += -Wignored-qualifiers -Wunused-but-set-parameter
> -COMMON_CFLAGS += -Werror
> +COMMON_CFLAGS += -Wall -Wwrite-strings -Wempty-body -Wuninitialized
> +COMMON_CFLAGS += -Wignored-qualifiers -Werror
> +
>  frame-pointer-flag=-f$(if $(KEEP_FRAME_POINTER),no-,)omit-frame-pointer
>  fomit_frame_pointer := $(call cc-option, $(frame-pointer-flag), "")
>  fnostack_protector := $(call cc-option, -fno-stack-protector, "")
>  fnostack_protector_all := $(call cc-option, -fno-stack-protector-all, "")
> -wno_frame_address := $(call cc-option, -Wno-frame-address, "")
>  fno_pic := $(call cc-option, -fno-pic, "")
>  no_pie := $(call cc-option, -no-pie, "")
>  COMMON_CFLAGS += $(fomit_frame_pointer)
>  COMMON_CFLAGS += $(fno_stack_protector)
>  COMMON_CFLAGS += $(fno_stack_protector_all)
> -COMMON_CFLAGS += $(wno_frame_address)
>  COMMON_CFLAGS += $(if $(U32_LONG_FMT),-D__U32_LONG_FMT__,)
>  COMMON_CFLAGS += $(fno_pic) $(no_pie)
>  
> +COMMON_CFLAGS += $(call cc-option, -Wno-frame-address, "")

I think the old code used ":=" on purpose, so that the test is only done
once. With your new code, the test is now done each time COMMON_CFLAGS
gets evaluated, i.e. for each compiled object.

Could you please rewrite this test to use the ":=" detour for all lines
that call cc-option?

 Thanks,
  Thomas