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

[Ananyev, Konstantin]

> -----Original Message-----
> From: Marc Sune [mailto:marc.sune at bisdn.de]
> Sent: Tuesday, March 03, 2015 2:39 PM
> To: Ananyev, Konstantin; Richardson, Bruce
> Cc: dev at dpdk.org
> Subject: Re: [dpdk-dev] [PATCH] mk: add support for gdb debug info generation
> 
> 
> On 03/03/15 14:31, Ananyev, Konstantin wrote:
> >
> >> -----Original Message-----
> >> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Bruce Richardson
> >> Sent: Tuesday, March 03, 2015 1:03 PM
> >> To: Marc Sune
> >> Cc: dev at dpdk.org
> >> Subject: Re: [dpdk-dev] [PATCH] mk: add support for gdb debug info generation
> >>
> >> 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. 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]
> >>
> > Well, but then people would say 'why only -g -O0' for _DEBUG config option?
> > And would ask for ability to add/change other compile options to add/change for particular library.
> > If we need that, probably we can introduce RTE_LIBRTE_<LIBNAME>_EXTRA_CFLAGS config macros for each library?
> > So people can set them in their config files to whatever they like?
> 
> It is not a bad idea either. However, there are already those _DEBUG
> config elements (the KNI is a special case).

> 
> Maybe both can be combined (i.e. RTE_LIBRTE_<LIBNAME>_EXTRA_CFLAGS
> should always override _DEBUG). It would probably get a bit
> over-engineered then, though.

I would probably leave _DEBUG config options with what they are doing right now:
perform extra checks and generate logs.
After all, people might want their program to be more verbose, but they don't want compile options to be changed.  

Konstantin

> 
> marc
> >
> > Konstantin