[Buildroot] Libraries built with buildroot can only be used by buildroot itself.

[Thomas De Schampheleire]

Hi,

On Tue, Jul 30, 2013 at 6:40 AM, Woody Wu <narkewoody at gmail.com> wrote:
> Hi,
>
> ** In below example, I will talk directfb libraries, but I am afraid it it
>    not specific to directfb but a more general case.
>
> Using buildroot and BR2_TOOLCHAIN_EXTERNAL_CODESOURCERY_ARM201203, I got
> build with some graphics libraries (in my case, these are direct frame
> buffer libraries, i.e., BR2_PACKAGE_DIRECTFB). Then I want to use these
> cross compiled libraries to cross compile my own written very simple
> directfb application code.
>
>
> What I did is:
>
>     crossroot=/home/woody/buildroot-2013.05/
>         output/host/usr/arm-buildroot-linux-gnueabi/sysroot
>     rm -f *.o hline
>     arm-none-linux-gnueabi-gcc -I ${crossroot}/usr/include/directfb \
>         -D_GNU_SOURCE -o hline.o -c hline.c
>     arm-none-linux-gnueabi-gcc -I ${crossroot}/usr/include/directfb \
>         -D_GNU_SOURCE -o hline hline.o -ldirectfb -L ${crossroot}/usr/lib
>
> In case one, I set my path to use the gcc from my own Codesourcery
> installation, which is the same version as that buildroot is using.
> Actually, this Codesourcery installation is a direct uncompress from the
> tarball that buildroot downloaded from net to its download directory.
>
> In case two, I set my path to use the gcc directly in buildroot, i.e,
> under /home/woody/buildroot-2013.05/host/usr/bin
>
> In case two, it built with success. But case one, it did not:
>
> /home/woody/arm-2012.03/bin/../lib/gcc/arm-none-linux-gnueabi/4.6.3/../../../../arm-none-linux-gnueabi/bin/ld: skipping incompatible /lib/libc.so.6 when searching for /lib/libc.so.6
> /home/woody/arm-2012.03/bin/../lib/gcc/arm-none-linux-gnueabi/4.6.3/../../../../arm-none-linux-gnueabi/bin/ld: cannot find /lib/libc.so.6
> /home/woody/arm-2012.03/bin/../lib/gcc/arm-none-linux-gnueabi/4.6.3/../../../../arm-none-linux-gnueabi/bin/ld: skipping incompatible /usr/lib/libc_nonshared.a when searching for /usr/lib/libc_nonshared.a
> /home/woody/arm-2012.03/bin/../lib/gcc/arm-none-linux-gnueabi/4.6.3/../../../../arm-none-linux-gnueabi/bin/ld: cannot find /usr/lib/libc_nonshared.a
> /home/woody/arm-2012.03/bin/../lib/gcc/arm-none-linux-gnueabi/4.6.3/../../../../arm-none-linux-gnueabi/bin/ld: cannot find /lib/ld-linux.so.3
> collect2: ld returned 1 exit status
>
>
> I don't understand why the error happened.  It seems the cross compiler
> of buildroot understood things correctly, but the same cross compiler
> install by myself did not.
>
> Can anyone please give me hint?

Buildroot creates a toolchain wrapper when using external toolchains.
This wrapper passes some extra arguments to the toolchain, telling it
where the sysroot is containing the headers and libraries, which
architecture to build for etc. This wrapper is what you see in
output/host/usr/bin.

You can verify that this is the case by running strace on it, or, if
you have a very recent buildroot version (containing commit
aaa06aaa82787b77ea56a7664cb4b0a22eca5c31, you can get a list of all
options passed by setting the environment variable BR_DEBUG_WRAPPER
when running the toolchain.

For your reference, the wrapper source is at
toolchain/toolchain-external/ext-toolchain-wrapper.c


So the behavior you are seeing is expected. You should always use the
toolchain through output/host/usr/bin/.

Best regards,
Thomas