[gentoo-soc] cross_container_support - progress report #10

[gentoo-soc] cross_container_support - progress report #10

[Jing Huang]

Hi,

== Progress of last Week ==

In the last week, I made armv7a-hardfloat-linux-gnueabi-gcc [ELF
32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically
linked (uses shared libs), for GNU/Linux 2.6.9, stripped] run in the
arm chroot.

Firstly, I think it is very difficult to switch dynamic libraries
using ld.so.conf and ldconfig, because the generated ld.so.cache
always includes /lib.
My investigation shows:

glibc-2.14.1/Makeconfig:
# Where to install the shared library and dynamic linker.
ifndef slibdir
slibdir = $(exec_prefix)/lib
endif

glibc-2.14.1/elf/Makefile:
CFLAGS-ldconfig.c = $(SYSCONF-FLAGS) -D'LIBDIR="$(libdir)"' \
		    -D'SLIBDIR="$(slibdir)"' -DIS_IN_ldconfig=1

glibc-2.14.1/elf/ldconfig.c:
  if (!opt_only_cline)
    {
      parse_conf (config_file, true);

      /* Always add the standard search paths.  */
      add_system_dir (SLIBDIR);
      if (strcmp (SLIBDIR, LIBDIR))
	    add_system_dir (LIBDIR);
    }

Therefore, ldconfig will always include /lib library path unless using
"ldconfig -n xxx". But "ldconfig -n" won't generate new ld.so.cache.

Actually, the linker seeks libraries following the sequence:
a. DT_RPATH in dynamic section.
b. LD_LIBRARY_PATH environment variable.
c. ld.so.cache

Instead, I was using LD_LIBRARY_PATH rather than ld.so.conf. The steps are:

1. mount native libs to chroot
mount --bind /lib gentoo-rootfs/native/lib
mount --bind /usr/lib gentoo-rootfs/native/usr/lib
mount --bind /usr/local/lib gentoo-rootfs/native/usr/local/lib
mount --bind /usr/i686-pc-linux-gnu gentoo-rootfs/native/usr/i686-pc-linux-gnu

2. start arm chroot and link native libs
./lxc.sh start -n gentoo-arm
export LD_LIBRARY_PATH="/native/lib:/native/usr/lib:/native/usr/local/lib"

3. set up dynamic library interpreter
ln -s /native/lib/ld-2.14.1.so /lib/ld-linux.so.2

4. running native armv7a-hardfloat-linux-gnueabi-gcc
./native/usr/i686-pc-linux-gnu/armv7a-hardfloat-linux-gnueabi/gcc-bin/4.5.3/armv7a-hardfloat-linux-gnueabi-gcc
build an arm program using armv7a-hardfloat-linux-gnueabi-gcc successfully

== Plans for this week ==

1. Integrate my progress into lxc.sh script
2. get some valuations comparing native gcc and emulated gcc
3. document all the steps in the wiki

[gentoo-soc] Re: cross_container_support - progress report #10

[Luca Barbato]

On 08/07/2012 06:37 PM, Jing Huang wrote:
> Hi,
> 
> == Progress of last Week ==
> 
> In the last week, I made armv7a-hardfloat-linux-gnueabi-gcc [ELF
> 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically
> linked (uses shared libs), for GNU/Linux 2.6.9, stripped] run in the
> arm chroot.
> 
> Firstly, I think it is very difficult to switch dynamic libraries
> using ld.so.conf and ldconfig, because the generated ld.so.cache
> always includes /lib.
> My investigation shows:
> 
> glibc-2.14.1/Makeconfig:
> # Where to install the shared library and dynamic linker.
> ifndef slibdir
> slibdir = $(exec_prefix)/lib
> endif
> 

slibdir can be lib in arm and lib64 in stock amd64, that's the trick I'm
using currently.

> glibc-2.14.1/elf/Makefile:
> CFLAGS-ldconfig.c = $(SYSCONF-FLAGS) -D'LIBDIR="$(libdir)"' \
> 		    -D'SLIBDIR="$(slibdir)"' -DIS_IN_ldconfig=1
> 
> glibc-2.14.1/elf/ldconfig.c:
>   if (!opt_only_cline)
>     {
>       parse_conf (config_file, true);
> 
>       /* Always add the standard search paths.  */
>       add_system_dir (SLIBDIR);
>       if (strcmp (SLIBDIR, LIBDIR))
> 	    add_system_dir (LIBDIR);
>     }
> 
> Therefore, ldconfig will always include /lib library path unless using
> "ldconfig -n xxx". But "ldconfig -n" won't generate new ld.so.cache.

Probably patching ldconfig could be an option if using the env var does not.

> Actually, the linker seeks libraries following the sequence:
> a. DT_RPATH in dynamic section.
> b. LD_LIBRARY_PATH environment variable.
> c. ld.so.cache
> 
> Instead, I was using LD_LIBRARY_PATH rather than ld.so.conf. The steps are:
> 
> 1. mount native libs to chroot
> mount --bind /lib gentoo-rootfs/native/lib
> mount --bind /usr/lib gentoo-rootfs/native/usr/lib
> mount --bind /usr/local/lib gentoo-rootfs/native/usr/local/lib
> mount --bind /usr/i686-pc-linux-gnu gentoo-rootfs/native/usr/i686-pc-linux-gnu
> 
> 2. start arm chroot and link native libs
> ./lxc.sh start -n gentoo-arm
> export LD_LIBRARY_PATH="/native/lib:/native/usr/lib:/native/usr/local/lib"
> 
> 3. set up dynamic library interpreter
> ln -s /native/lib/ld-2.14.1.so /lib/ld-linux.so.2
> 
> 4. running native armv7a-hardfloat-linux-gnueabi-gcc
> ./native/usr/i686-pc-linux-gnu/armv7a-hardfloat-linux-gnueabi/gcc-bin/4.5.3/armv7a-hardfloat-linux-gnueabi-gcc
> build an arm program using armv7a-hardfloat-linux-gnueabi-gcc successfully

That is a passable solution, pending some bashrc tricks in portage.

> == Plans for this week ==
> 
> 1. Integrate my progress into lxc.sh script
> 2. get some valuations comparing native gcc and emulated gcc
> 3. document all the steps in the wiki

Sounds good. The impressive difference is made by native coreutils
(beware to not override uname), make and such.

lu