Re: [PATCH] mk: fix underlinking issues of most librte libraries

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 5/24/2016 11:11 AM, Christian Ehrhardt wrote:
> Hi Panu,
> I already agreed to Thomas on IRC but won't have time until next week.
> Thanks for making a patch that does that already - I'll give it a look and
> some test on my end next week then.
> 
> 
> 
> Christian Ehrhardt
> Software Engineer, Ubuntu Server
> Canonical Ltd
> 
> On Tue, May 24, 2016 at 11:56 AM, Panu Matilainen <pmatilai@redhat.com>
> wrote:
> 
>> On 05/20/2016 08:08 PM, Thomas Monjalon wrote:
>>
>>> 2016-05-20 18:50, Christian Ehrhardt:
>>>
>>>> The individual libraries have various cross dependencies.
>>>> This is already refelcted in the DEPDIR dependency, but not yet in
>>>> proper DT_NEEDED flags in the .so's.
>>>> This adds the -l flags so that is properly stored in the .so's ELF
>>>> headers.
>>>>
>>>
>>> Why not filling LDLIBS by parsing DEPDIRS-y in rte.lib.mk?
>>>
>>>
>> A fair question :) The thought has passed my mind too, but I thought it'd
>> be too messy with differing library vs directory names and other
>> exceptions. But in reality manually maintained separate LDLIBS is only
>> going to get out of sync sooner or later, and turns out its not that bad
>> anyway:
>>
>> diff --git a/mk/rte.lib.mk b/mk/rte.lib.mk
>> index b420280..88b4e98 100644
>> --- a/mk/rte.lib.mk
>> +++ b/mk/rte.lib.mk
>> @@ -77,6 +77,12 @@ else
>>  _CPU_LDFLAGS := $(CPU_LDFLAGS)
>>  endif
>>
>> +# Translate DEPDIRS-y into LDLIBS
>> +IGNORE_DEPS = -lrte_eal/% -lrte_net -lrte_compat
>> +_LDDIRS = $(subst librte_ether,libethdev,$(DEPDIRS-y))
>> +_LDDEPS = $(subst lib/lib,-l,$(_LDDIRS))
>> +LDLIBS += $(filter-out $(IGNORE_DEPS), $(_LDDEPS))
>> +
>>  O_TO_A = $(AR) crDs $(LIB) $(OBJS-y)
>>  O_TO_A_STR = $(subst ','\'',$(O_TO_A)) #'# fix syntax highlight
>>  O_TO_A_DISP = $(if $(V),"$(O_TO_A_STR)","  AR $(@)")
>>
>> I'm also sure somebody more familiar with gmake could improve it, but it
>> seems to work quite fine here. I'll wait a bit to see if there are other
>> suggestions before sending it as a proper patch.
>>
>>         - Panu -
>>

I did test the patch with minor diff in rte.vars.mk [1], otherwise all
libraries kept needed in final library.

Patch itself looks good, overlinking problem in final binary seems fixed
[2] [3].

But this cause a compilation error for cmdline_test [4]. This is because
of cyclic dependency between librte_eal <-> librte_mempool.

Other applications don't have this compilation error because they use
librte_mempool, and since it is linked against application,  this error
not observed. cmdline_test itself doesn't have any direct call to
librte_mempool.

It is possible to add workaround to cmdline_test [5], (introduce
overlinking back), but should we attack on cyclic dependency instead?


Thanks,
ferruh

---

[1]
diff --git a/mk/exec-env/linuxapp/rte.vars.mk
b/mk/exec-env/linuxapp/rte.vars.mk
index d51bd17..10d37d5 100644
--- a/mk/exec-env/linuxapp/rte.vars.mk
+++ b/mk/exec-env/linuxapp/rte.vars.mk
@@ -46,7 +46,7 @@ EXECENV_CFLAGS  = -pthread
 endif

 # Workaround lack of DT_NEEDED entry
-EXECENV_LDFLAGS = --no-as-needed
+EXECENV_LDFLAGS = --as-needed

 EXECENV_LDLIBS  =
 EXECENV_ASFLAGS =


[2]
# ldd build/app/testpmd
        linux-vdso.so.1 (0x00007ffcff92e000)
        librte_mbuf.so.2.1 => .../build/lib/librte_mbuf.so.2.1
        libethdev.so.4.1 => .../build/lib/libethdev.so.4.1
        librte_mempool.so.2.1 => .../build/lib/librte_mempool.so.2.1
        librte_ring.so.1.1 => .../build/lib/librte_ring.so.1.1
        librte_eal.so.2.1 => .../build/lib/librte_eal.so.2.1
        librte_cmdline.so.2.1 => .../build/lib/librte_cmdline.so.2.1
        librte_pmd_bond.so.1.1 => .../build/lib/librte_pmd_bond.so.1.1
        libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f6879ff1000)
        libc.so.6 => /lib64/libc.so.6 (0x00007f6879c30000)
        /lib64/ld-linux-x86-64.so.2 (0x0000564998dbd000)
        libdl.so.2 => /lib64/libdl.so.2 (0x00007f6879a2c000)
        libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007f6879814000)
        librt.so.1 => /lib64/librt.so.1 (0x00007f687960c000)
        librte_kvargs.so.1.1 => .../build/lib/librte_kvargs.so.1.1

[3]
# ldd -u -r build/app/testpmd
#


[4]
== Build app/cmdline_test
  CC cmdline_test.o
  CC commands.o
  LD cmdline_test
.../build/lib/librte_eal.so: undefined reference to `rte_mempool_lookup'
.../build/lib/librte_eal.so: undefined reference to `rte_mempool_create'
collect2: error: ld returned 1 exit status
.../mk/rte.app.mk:243: recipe for target 'cmdline_test' failed
make[3]: *** [cmdline_test] Error 1


[5]
diff --git a/app/cmdline_test/Makefile b/app/cmdline_test/Makefile
index c6169f5..69ebfb2 100644
--- a/app/cmdline_test/Makefile
+++ b/app/cmdline_test/Makefile
@@ -46,6 +46,7 @@ SRCS-y += commands.c

 CFLAGS += -O3
 CFLAGS += $(WERROR_FLAGS)
+LDFLAGS += --no-as-needed

 # this application needs libraries first
 DEPDIRS-y += lib drivers