[OE-core] Query for multilib support in Yocto

[Luo Zhenhua-B19537]

Hi all, 

I am trying the multilib feature of Yocto, and I want to make sure if below scenarios are supported, who can help to clarify? Thanks in advance. 

For standalone toolchain built by "bitbake meta-toolchain"
1. Can the same gcc binary build both 32b and 64b applications or two different gcc binaries(one is for 32b, the other is for 64b) are required? 

For gcc with multilib support running on target board
1. Can the same gcc binary build both 32b and 64b applications or two different gcc binaries(one is for 32b, the other is for 64b) are required? 
2. Can both 32b and 64b application be executed in the same rootfs image with multilib support?

BTW, may I know how the default value of LIBRARY_PATH is set? I experienced following error when I use gcc(32bit rootfs with multilib support) to do 64b build, I find the linker search libraries in /usr/lib and /lib instead of /usr/lib64 and /lib64. 

root at p5020ds:~# gcc -m64 my_test.c -o my_test
/usr/lib/gcc/powerpc-poky-linux/4.7.2/../../../../powerpc-poky-linux/bin/ld: skipping incompatible /usr/lib/gcc/powerpc-poky-linux/4.7.2/../../../powerpc-poky-linux/4.7.2/libgcc.a when searching for -lgcc
/usr/lib/gcc/powerpc-poky-linux/4.7.2/../../../../powerpc-poky-linux/bin/ld: skipping incompatible /usr/lib/powerpc-poky-linux/4.7.2/libgcc.a when searching for -lgcc
/usr/lib/gcc/powerpc-poky-linux/4.7.2/../../../../powerpc-poky-linux/bin/ld: cannot find -lgcc
/usr/lib/gcc/powerpc-poky-linux/4.7.2/../../../../powerpc-poky-linux/bin/ld: skipping incompatible /lib/../lib/libgcc_s.so.1 when searching for libgcc_s.so.1
/usr/lib/gcc/powerpc-poky-linux/4.7.2/../../../../powerpc-poky-linux/bin/ld: skipping incompatible //lib/libgcc_s.so.1 when searching for libgcc_s.so.1
/usr/lib/gcc/powerpc-poky-linux/4.7.2/../../../../powerpc-poky-linux/bin/ld: cannot find libgcc_s.so.1
/usr/lib/gcc/powerpc-poky-linux/4.7.2/../../../../powerpc-poky-linux/bin/ld: skipping incompatible /usr/lib/gcc/powerpc-poky-linux/4.7.2/../../../powerpc-poky-linux/4.7.2/libgcc.a when searching for libgcc.a
/usr/lib/gcc/powerpc-poky-linux/4.7.2/../../../../powerpc-poky-linux/bin/ld: skipping incompatible /usr/lib/powerpc-poky-linux/4.7.2/libgcc.a when searching for libgcc.a
/usr/lib/gcc/powerpc-poky-linux/4.7.2/../../../../powerpc-poky-linux/bin/ld: cannot find libgcc.a
collect2: error: ld returned 1 exit status
root at p5020ds:~# cat my_test.c 
int main()
{
    int a=0;

    return a;
}


Best Regards,

Zhenhua