Re: [PATCH v4 1/2] Simplify the ifdefs in rte.app.mk.

["Wiles, Keith" <keith.wiles-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>]

On 4/30/15, 11:22 AM, "Richardson, Bruce" <bruce.richardson-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
wrote:

>On Thu, Apr 30, 2015 at 02:31:13PM +0000, Wiles, Keith wrote:
>> 
>> 
>> On 4/30/15, 8:38 AM, "Olivier MATZ" <olivier.matz-pdR9zngts4EAvxtiuMwx3w@public.gmane.org> wrote:
>> 
>> >Hi Keith,
>> >
>> >On 04/30/2015 03:24 PM, Wiles, Keith wrote:
>> >>
>> >>
>> >> On 4/30/15, 4:45 AM, "Olivier MATZ" <olivier.matz-pdR9zngts4EAvxtiuMwx3w@public.gmane.org> wrote:
>> >>
>> >>> Hi Keith,
>> >>>
>> >>> Thank you for submitting a clean-up. Please see some comments below.
>> >>>
>> >>> On 04/29/2015 05:25 PM, Keith Wiles wrote:
>> >>>> Trying to simplify the ifdefs in rte.app.mk to make the code
>> >>>> more readable and maintainable by moving LDLIBS variable to use
>> >>>> the same style as LDLIBS-y being used in the rest of the code.
>> >>>>
>> >>>> Added a new variable called EXTRA_LDLIBS to be used by example apps
>> >>>> instead of using LDLIBS directly.
>> >>>
>> >>> If I understand well, the goal of this patch is only a cleanup in
>> >>> rte.app.mk, but at the end, it changes the makefile user "API",
>> >>> which could probably be a problem for applications using the
>> >>> dpdk makefile framework.
>> >>>
>> >>> Why not just having an temporary internal variable (let's say
>> >>> _LDLIBS-y) that would allow to do the clean-up without modifying
>> >>> the user interface?
>> >>>
>> >>> Also, with your patch, the approach for EXTRA_LDLIBS would be
>> >>> different than CFLAGS or LDFLAGS:
>> >>> - CFLAGS/LDFLAGS are in Makefiles only
>> >>> - EXTRA_CFLAGS/EXTRA_LDFLAGS are prefered in command line
>> >>>    to add flags to the default ones
>> >>>
>> >>> I'm not opposed to add EXTRA_LDLIBS in addition to LDLIBS,
>> >>> keeping a compatibility with existing application Makefiles.
>> >>
>> >> The docs for DPDK 28.3.6 states they can be used for both command
>>line
>> >>and
>> >> Makefile, so I think I like the current solution unless everyone
>>wants
>> >>it
>> >> as you suggested.
>> >>
>> >> 
>> 
>>>>http://dpdk.readthedocs.org/en/v2.0.0/prog_guide/dev_kit_build_system.h
>>>>tm
>> >>l
>> >
>> > From the link you have sent:
>> >
>> >- About CFLAGS:
>> >
>> >"28.3.4. Variables that Can be Set/Overridden in a Makefile Only
>> >[...]
>> >CFLAGS: Flags to use for C compilation. The user should use += to
>>append
>> >data in this variable."
>> >
>> >nothing in 28.3.6
>> >
>> >
>> >- About EXTRA_CFLAGS:
>> >
>> >nothing in 28.3.4
>> >
>> >"28.3.6. Variables that Can be Set/Overridden by the User in a Makefile
>> >or Command Line
>> >[...]
>> >EXTRA_CFLAGS: The content of this variable is appended after CFLAGS
>>when
>> >compiling."
>> 
>> The point was that EXTRA_XXX can be used for command line and Makefile
>>as
>> it was pointed out in a previous email the assumption was EXTRA_XXX was
>> only for the command line. (Just to make sure we understood EXTRA_XXX
>>was
>> not just for command line options.) This was the reason I sent the link
>>an
>> to point out using EXTRA_XXX is a much cleaner method then allowing
>> someone to modify what I believe is an internal variable.
>
>Just beware that setting EXTRA_* flags on the commandline can override
>their
>values in the makefiles, and cause unexpected compilation problems.
>Therefore,
>it tends to be best to avoid using the EXTRA_* variables for variables
>essential
>to compile. For example: putting "-g -O3" in EXTRA_CFLAGS is ok, as the
>if the
>useroverrides those with something else things should still work, but
>putting
>"-I/path/to/include" would not be.

On the command line and makefile you should be using += and not just = or
you run into this problem.
>
>/Bruce
>
>