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

[Thomas Huth <thuth@redhat.com>]

On 15/10/2019 09.57, Bill Wendling wrote:
> On Tue, Oct 15, 2019 at 12:29 AM Thomas Huth <thuth@redhat.com> wrote:
>>
>> 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?
>>
> Does it rerun the "cc-option" call if the COMMON_CFLAGS is initially
> defined with ":="?

It does not rerun the "cc-option" call in that case, but compilation
fails. I think it's likely due to the line that contains the "$(if
$(U32_LONG_FMT),-D__U32_LONG_FMT__,)" since that likely needs to be
evaluated dynamically.

 Thomas