Re: [PATCH] mk: add support for gdb debug info generation

[Panu Matilainen <pmatilai-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On 03/03/2015 02:19 PM, Marc Sune wrote:
>
> On 03/03/15 10:33, Bruce Richardson wrote:
>> On Mon, Mar 02, 2015 at 06:32:13PM +0100, Marc Sune wrote:
>>> On 22/02/15 12:51, Marc Sune wrote:
>>>> I don't like the proposed patch, but I am recovering this old thread
>>>> because I agree on the problem statement.
>>>>
>>>> On 04/04/14 11:57, Ananyev, Konstantin wrote:
>>>>> Hi Cyril,
>>>>> We already do have 'EXTRA_CFLAGS' and 'EXTRA_LDFLAGS' that you can use
>>>>> to enable debug, or any other compiler/linker options you need.
>>>>> Wonder, why that is not enough?
>>>> EXTRA_FLAGS var affects all the DPDK libraries. I was wondering why
>>>> setting individually:
>>>>
>>>> diff --git a/config/common_linuxapp b/config/common_linuxapp
>>>> index 2f9643b..04adc0d 100644
>>>> --- a/config/common_linuxapp
>>>> +++ b/config/common_linuxapp
>>>> @@ -127,7 +127,7 @@ CONFIG_RTE_LIBRTE_KVARGS=y
>>>> # Compile generic ethernet library
>>>> #
>>>> CONFIG_RTE_LIBRTE_ETHER=y
>>>> -CONFIG_RTE_LIBRTE_ETHDEV_DEBUG=n
>>>> +CONFIG_RTE_LIBRTE_ETHDEV_DEBUG=y
>>>>
>>>>
>>>> to put an example, does not set -g and -O0 in that particular module
>>>> only.
>>>> No one would ever use something compiled in DEBUG in production anyway.
>>>>
>>>> I always end up modifying manually Makefiles in the lib library that
>>>> I am
>>>> interested in having insides, overriding CFLAGS=-O3, which is not that
>>>> nice.
>>> I would like some feedback on this idea. If the community sees
>>> benefit, I
>>> will work on a patch for this.
>>>
>>> Marc
>>>
>> So, your proposal is to patch things so that any time one sets DEBUG=y
>> in the
>> build-time config for a library, we change the '-O3' to '-O0' and set
>> -g also.
>> Correct?
>
> I am not sure what you mean by 'patch things'. I would simply enable the
> build system to override the default compilation flags (now DPDK-wide,
> or specifically librte_ wide) when _DEBUG=y for a library, changing
> compilation flags from -O3 to -O0 -g and possibly also -fno-inline. I
> have to check if -O0 already implicitly means -fno-inline (even for
> __attribute__((always_inline)) ).
>
> I did a quick test. I chose KNI because it didn't have a DEBUG flag for
> the user-space library. For other libraries, the existing _DEBUG setting
> would be enough:
>
> marc@dpdk:~/dpdk$ git diff HEAD
> diff --git a/config/common_linuxapp b/config/common_linuxapp
> index 97f1c9e..8a3cef8 100644
> --- a/config/common_linuxapp
> +++ b/config/common_linuxapp
> @@ -405,6 +405,7 @@ CONFIG_RTE_LIBRTE_PIPELINE=y
>   #
>   CONFIG_RTE_LIBRTE_KNI=y
>   CONFIG_RTE_KNI_PREEMPT_DEFAULT=y
> +CONFIG_RTE_LIBRTE_KNI_DEBUG=y
>   CONFIG_RTE_KNI_KO_DEBUG=n
>   CONFIG_RTE_KNI_VHOST=n
>   CONFIG_RTE_KNI_VHOST_MAX_CACHE_SIZE=1024
> diff --git a/lib/librte_kni/Makefile b/lib/librte_kni/Makefile
> index 7107832..895f64e 100644
> --- a/lib/librte_kni/Makefile
> +++ b/lib/librte_kni/Makefile
> @@ -34,7 +34,7 @@ include $(RTE_SDK)/mk/rte.vars.mk
>   # library name
>   LIB = librte_kni.a
>
> -CFLAGS += $(WERROR_FLAGS) -I$(SRCDIR) -O3 -fno-strict-aliasing
> +CFLAGS += $(WERROR_FLAGS) -I$(SRCDIR) $(CONFIG_RTE_LIBRTE_KNI_CFLAGS)
>
>   EXPORT_MAP := rte_kni_version.map
>
> diff --git a/mk/rte.app.mk b/mk/rte.app.mk
> index 63a41e2..eee477d 100644
> --- a/mk/rte.app.mk
> +++ b/mk/rte.app.mk
> @@ -78,6 +78,13 @@ endif
>   ifeq ($(CONFIG_RTE_LIBRTE_KNI),y)
>   ifeq ($(CONFIG_RTE_EXEC_ENV_LINUXAPP),y)
>   LDLIBS += -lrte_kni
> +
> +ifeq ($(CONFIG_RTE_LIBRTE_KNI_DEBUG),y)
> +CONFIG_RTE_LIBRTE_KNI_CFLAGS = -O0 -g -fno-strict-aliasing -fno-inline
> +else
> +CONFIG_RTE_LIBRTE_KNI_CFLAGS = -O3 -fno-strict-aliasing
> +endif
> +
>   endif
>   endif
>
>
> Thoughts?

My 5c is that if anything, DPDK needs *less* places that muck around 
with compiler flags, not more. If you something like this for all the 
libraries in DPDK the number doesn't just increase a bit, it explodes.

I dont see that much point in this thing, but I'd approach it by 
defining the debug flags someplace central, say DEBUG_FLAGS, and append 
that to the common cflags when *_DEBUG config is enabled. At least with 
gcc the last option wins so if you just append -O0 when debugging then 
that's what wins, the earlier -O3 does not matter.

	- Panu -

	- Panu -