[dpdk-dev] [PATCH] mk: add support for gdb debug info generation

[Marc Sune]

On 03/03/15 14:03, Bruce Richardson wrote:
> On Tue, Mar 03, 2015 at 01:56:19PM +0100, Marc Sune wrote:
>> On 03/03/15 13:40, Panu Matilainen wrote:
>>> 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 at 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.
>> If you check the part below this one in my original email, that you stripped
>> out (without notice), the suggestion was also to add a global _DEBUG
>> parameter for the entire DPDK set of libraries, to change all the CFLAGS at
>> once (not in the attached PATCH).
>>
>>> 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.
>> The original problem is the one you expose; libraries hardcode the CFLAGS,
>> ignoring user-flags. There is no way to change this unless you change the
>> Makefiles directly.
>>
>> But right now, each library does hardcode its *own* flags (check Makefiles
>> for the libraries), so there is already not a unified approach here. I see
>> for instance KNI having -fno-strict-aliasing while other libraries don't.
>>
>> Having said that, there are moments, specially with -O3, in which to be able
>> to reproduce a bug, you need to compile certain parts of code with -O3 and
>> the rest with -O0 -g (the ones to be debugged). The approach proposed (both
>> a global *and* a lib specific) allows that.
>>
>> Marc
>>
> I believe that the global option of overriding the CFLAGS is already sufficiently
> covered - including being documented in programmers guide - by EXTRA_CFLAGS.

To be honest, I tried EXTRA_CFLAGS at some point in time (probably 1.5 
or 1.6, but maybe not stable releases) and it did not work, so I ended 
up doing it manually, and never tried again.

It does work now with CFLAGS, I didn't try LDFLAGS, but it does not for 
EXTRA_CPPFLAGS apparently (unless I made some stupid mistake):

marc at dpdk:~/dpdk$ git diff
diff --git a/lib/librte_kni/rte_kni.c b/lib/librte_kni/rte_kni.c
index 4e70fa0..4a1e538 100644
--- a/lib/librte_kni/rte_kni.c
+++ b/lib/librte_kni/rte_kni.c
@@ -61,6 +61,10 @@

  #define KNI_MEM_CHECK(cond) do { if (cond) goto kni_fail; } while (0)

+#ifdef TEST_CPPFLAGS
+       #error TEST_CPPFLAGS defined
+#endif
+
  /**
   * KNI context
   */

marc at dpdk:~/dpdk$ export EXTRA_CPPFLAGS='-DTEST_CPPFLAGS'
marc at dpdk:~/dpdk$ make install T=x86_64-native-linuxapp-gcc
...
Build complete
marc at dpdk:~/dpdk$

> The
> ability to turn off optimization support for a single library is not covered
> anywhere, and that suggestion seems reasonable to me. For each library, we can
> just append '-O0 -g' to the CFLAGS in that libraries makefile if the debug option
> is set. I don't see that as significantly complicating things [though I wouldn't
> make any changes to the rte.app.mk to allow this, just have it per lib in the
> lib's makefile]

Right. It makes more sense there.

Marc

>
> /Bruce
>
>>>     - Panu -
>>>
>>>     - Panu -
>>>