Re: [dpdk-dev] [PATCH 1/2] mk: prevent overlinking in applications

[Thomas Monjalon <thomas.monjalon@6wind.com>]

Hi Ferruh,

2016-05-27 17:48, Ferruh Yigit:
> Replace --no-as-needed linker flag with --as-needed flag, which will
> only link libraries directly called by application. This requires inter
> library dependencies resolved correctly.
> 
> Not linking all libraries cause a compile error for lpcap and possible
> to have other similar compiler errors, so increasing the scope of
> --start-group argument.

What is the error?

> cmdline_test application causes compile error because of cyclic
> dependency between librte_eal <-> librte_mempool. A workaround added to
> cmdline_test for compile error.
> 
> Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>

> --- a/app/cmdline_test/Makefile
> +++ b/app/cmdline_test/Makefile
> @@ -46,6 +46,7 @@ SRCS-y += commands.c
>  
>  CFLAGS += -O3
>  CFLAGS += $(WERROR_FLAGS)

A comment is required here to explain the workaround.

> +LDFLAGS += -no-as-needed

The option should be --no-as-needed.

> --- 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

This comment is obsolete now.

> -EXECENV_LDFLAGS = --no-as-needed
> +EXECENV_LDFLAGS = --as-needed

Why put this option for Linux only?
Shouldn't we restrict this option to app.mk only?

> --- a/mk/rte.app.mk
> +++ b/mk/rte.app.mk
> @@ -58,6 +58,7 @@ _LDLIBS-y += -L$(RTE_SDK_BIN)/lib
>  #
>  
>  _LDLIBS-y += --whole-archive
> +_LDLIBS-y += --start-group

--start-group must be used only to solve circular dependencies.
Ideally we should not use it. I think it's needed only because
of EAL logs using mempool (must be removed).
Why extending it?
I'm afraid we are masking some issues.

>  _LDLIBS-$(CONFIG_RTE_LIBRTE_DISTRIBUTOR)    += -lrte_distributor
>  _LDLIBS-$(CONFIG_RTE_LIBRTE_REORDER)        += -lrte_reorder
> @@ -111,8 +112,6 @@ _LDLIBS-y                                   += -lcrypto
>  endif
>  endif # !CONFIG_RTE_BUILD_SHARED_LIBS
>  
> -_LDLIBS-y += --start-group
> -
>  _LDLIBS-$(CONFIG_RTE_LIBRTE_KVARGS)         += -lrte_kvargs
>  _LDLIBS-$(CONFIG_RTE_LIBRTE_MBUF)           += -lrte_mbuf
>  _LDLIBS-$(CONFIG_RTE_LIBRTE_IP_FRAG)        += -lrte_ip_frag