[vdr] [Makefile] `-fPIC` not added to externally defined `C[XX]FLAGS` of PLUGINS if `Make.config` not available

[Paul Menzel]

Dear VDR users,


in `Make.config.template` [1] which if renamed to `Make.config` gets
included in all Makefiles there is

        ifdef PLUGIN
        CFLAGS   += -fPIC
        CXXFLAGS += -fPIC
        DEFINES += -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE
        endif

which just gets included if `PLUGIN` is defined, which is normally done
in the Makefile of a plugin as for example in `Makefile` [3] belonging
to the plugin hello [2].

Additionally in each Makefile of a plugin `C[XX]FLAGS` is set to

        CXXFLAGS ?= -fPIC -g -O2 -Wall -Woverloaded-virtual -Wno-parentheses

if it has not been defined yet for example in the environment.

As far as I understand plugins have to be compiled with the `-fPIC`
flag, so that the VDR can be linked against them [4]. Otherwise it would
give an error message as the following example.

        ld: hello.o: relocation R_ARM_MOVW_ABS_NC against `a local symbol' can not be used when making a shared object; recompile with -fPIC
        hello.o: could not read symbols: Bad value

The problem now is, that if `Make.config` does not contain the snippet
from the top and `C[XX]FLAGS` are defined before without `-fPIC`
building the plugins fails. This scenario is typical in cross
compilation [5].

I do not know if the `DEFINES` from above are required, so I just
concentrate on the `-fPIC` issue because this flag is needed for a
successful build.

I thought of two solutions. Maybe you see something better.

1. Each `Makefile` of a plugin gets rewritten to always append `-fPIC`
to `C[XX]FLAGS`. Here is an example for the plugin hello.

        diff --git a/PLUGINS/src/hello/Makefile b/PLUGINS/src/hello/Makefile
        index ea5b806..a02d6c2 100644
        --- a/PLUGINS/src/hello/Makefile
        +++ b/PLUGINS/src/hello/Makefile
        @@ -18,7 +18,8 @@ VERSION = $(shell grep 'static const char \*VERSION *=' $(PLUGIN).c | awk '{ pri
         ### The C++ compiler and options:
         
         CXX      ?= g++
        -CXXFLAGS ?= -fPIC -g -O2 -Wall -Woverloaded-virtual -Wno-parentheses
        +CXXFLAGS ?= -g -O2 -Wall -Woverloaded-virtual -Wno-parentheses
        +CXXFLAGS += -fPIC
         
         ### The directory environment:

2. If `DEFINES` from the beginning is also needed, that we should factor
the snippet out into a file `Make.plugins` and every plugin has to
include it in its Makefile.

What do you think? What alternative is preferable? When this is decided
I would create a patch to change that in VDR.


Thanks,

Paul


[1] http://git.gekrumbel.de/vdr.git?p=vdr.git;a=blob;f=Make.config.template
[2] http://git.gekrumbel.de/vdr.git?p=vdr.git;a=tree;f=PLUGINS/src/hello
[3] http://git.gekrumbel.de/vdr.git?p=vdr.git;a=blob;f=PLUGINS/src/hello/Makefile#l31
[4] http://www.gentoo.org/proj/en/base/amd64/howtos/index.xml?part=1&chap=3
[5] http://lists.linuxtogo.org/pipermail/openembedded-devel/2010-January/016213.html
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