Eric Blake wrote:
> On 09/06/2012 12:07 AM, Jim Meyering wrote:
>> Eric Blake wrote:
>>
>>> I compiled on FreeBSD 8.2 (gcc 4.2.1), and when I updated to the latest
>>> gnulib, I started to see the following in config.log when running
>>> ./configure CFLAGS=-g:
>>>
>
>> When you configure with one set of warning options and later
>> build with another, as with your "make CFLAGS=-g", you're
>> short-circuiting the build tests. When I do that, I
>> simply turn off -Werror and ignore the warnings:
>>
>> make CFLAGS=-g WERROR_CFLAGS=
>
> But note that I did:
>
> ./configure CFLAGS=-g
Ah... I didn't read carefully enough.
> at the outset. Yes, I'm aware that _if_ you override CFLAGS at make
> time, you may have to also disable warnings at that time as well. But
> here, I'm talking about the case where I configured optimization to be
> off without needing to override CFLAGS at make time; that is, in a
> situation where we CAN run a configure test to see whether the warning
> will even be effective.
>
>>
>> Of course, you could simply rerun configure with CFLAGS=-g,
>
> Which is what I did...
>
>> and it would test each -W option individually...
>
> except that each -W option individually succeeds. -Wuninitialized only
> warns, not errors out, on this particular gcc 4.2.1 build. You _have_
> to test the combination of '-Wuninitialized -Werror' but no -O, in order
> to hit the failure. But I'm not sure how best to modify manywarnings.m4
> to do that testing. Then again, we've already special-cased
> -Wno-missing-field-initializer to work around gcc infelicities, so I
> guess I could enhance the module by adding another test along those lines.
Yes, it looks like if we're using both of those, we'll have to
add code to reject -Wuninitialized (maybe with a warning?) when
configuring without -O.
Actually, with GNU make, this is something that we could probably
adjust at make-time. And since we're typically enabling warnings
only when we have reasonable development tools, that might be even
better (simpler). E.g.,
[here's simple PoC, i.e., it doesn't know about -O0,
but you get the idea ]
W = -Wuninitialized -Werror
CFLAGS = -O
ifneq (,$(findstring -Wuninitialized,$(W)))
ifneq (,$(findstring -Werror,$(W)))
ifneq (,$(findstring -O,$(CFLAGS)))
W := $(subst -Wuninitialized,,$(W))
endif
endif
endif
all:
@echo $(W)
