Re: [dpdk-dev] [PATCH 1/3] mk: fix librte_pipeline dependency list truncation

[Bruce Richardson <bruce.richardson@intel.com>]

On Tue, Jun 21, 2016 at 01:25:52PM +0300, Panu Matilainen wrote:
> On 06/21/2016 01:01 PM, Dumitrescu, Cristian wrote:
> >
> >
> >>-----Original Message-----
> >>From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Panu Matilainen
> >>Sent: Tuesday, June 21, 2016 9:12 AM
> >>To: dev@dpdk.org
> >>Cc: christian.ehrhardt@canonical.com; thomas.monjalon@6wind.com
> >>Subject: [dpdk-dev] [PATCH 1/3] mk: fix librte_pipeline dependency list
> >>truncation
> >>
> >>In other libraries, dependency list is always appended to, but
> >>in commit 6cbf4f75e059 it with an assignment. This causes the
> >>librte_eal dependency added in commit 6cbf4f75e059 to get discarded,
> >>resulting in missing dependency on librte_eal.
> >>
> >>Fixes: b3688bee81a8 ("pipeline: new packet framework logic")
> >>Fixes: 6cbf4f75e059 ("mk: fix missing internal dependencies")
> >>
> >>Signed-off-by: Panu Matilainen <pmatilai@redhat.com>
> >>---
> >> lib/librte_pipeline/Makefile | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >>diff --git a/lib/librte_pipeline/Makefile b/lib/librte_pipeline/Makefile
> >>index 95387aa..a8f3128 100644
> >>--- a/lib/librte_pipeline/Makefile
> >>+++ b/lib/librte_pipeline/Makefile
> >>@@ -53,7 +53,7 @@ SYMLINK-$(CONFIG_RTE_LIBRTE_PIPELINE)-include +=
> >>rte_pipeline.h
> >>
> >> # this lib depends upon:
> >> DEPDIRS-$(CONFIG_RTE_LIBRTE_PIPELINE) += lib/librte_eal
> >>-DEPDIRS-$(CONFIG_RTE_LIBRTE_PIPELINE) := lib/librte_table
> >>+DEPDIRS-$(CONFIG_RTE_LIBRTE_PIPELINE) += lib/librte_table
> >> DEPDIRS-$(CONFIG_RTE_LIBRTE_PIPELINE) += lib/librte_port
> >>
> >> include $(RTE_SDK)/mk/rte.lib.mk
> >>--
> >>2.5.5
> >
> >
> >In release 16.4, EAL was missing from the dependency list, now it is added. The librte_pipeline uses rte_malloc, therefore it depends on librte_eal being present.
> >
> >In the Makefile of the other Packet Framework libraries (librte_port, librte_table), it looks like the first dependency in the list is EAL, which is listed with the assignment operator, followed by others that are listed with the append operator:
> >	DEPDIRS-$(CONFIG_RTE_LIBRTE_XYZ) := lib/librte_eal
> >	DEPDIRS-$(CONFIG_RTE_LIBRTE_XYZ) += lib/librte_some other lib
> >
> >Therefore, at least for cosmetic reasons, we should probably do the same in librte_pipeline, which requires changing both the librte_eal and the librte_table lines as below:
> >	DEPDIRS-$(CONFIG_RTE_LIBRTE_PIPELINE) := lib/librte_eal
> >	DEPDIRS-$(CONFIG_RTE_LIBRTE_PIPELINE) += lib/librte_table
> >	DEPDIRS-$(CONFIG_RTE_LIBRTE_PIPELINE) += lib/librte_port
> 
> Ah, didn't notice those because the assignment is first of the dependencies.
> 
> >
> >However, some other libraries e.g. librte_lpm simply add the EAL dependency using the append operator:
> >	DEPDIRS-$(CONFIG_RTE_LIBRTE_LPM) += lib/librte_eal
> >
> >To be honest, I need to refresh my knowledge on make, I don't remember right now when we should use the assignment and when the append. Do we need to use the assign for first dependency (EAL) and append for others or should we use append everywhere?
> 
> At least in automake, you need to assign before you can append. But in gmake
> this apparently is not the case, quoting from
> https://www.gnu.org/software/make/manual/html_node/Appending.html:
> 
> "When the variable in question has not been defined before, ‘+=’ acts just
> like normal ‘=’: it defines a recursively-expanded variable. However, when
> there is a previous definition, exactly what ‘+=’ does depends on what
> flavor of variable you defined originally."
> 
> So there's no need to use := anywhere for the dependencies, in fact its
> probably best avoided to avoid issues like this. Of course after the third
> patch in this "series" is applied, mistakes like these can no longer go
> unnoticed.
> 
Will the build be any slower with everything defaulting to recursively expanded
variables rather than the simply-expanded variables defined by the initial ":="?

/Bruce