Building an arm-unkown-linux-gnueabi GNU cross-compiler toolchain using crosstool-ng in order to compile code from an x86_64 GNU/Linux system to an ARM GNU/Linux system.

Building cross-compiler toolchains is complicated and in some cases using a prebuilt one might be preferable. For example, Ubuntu has a package for an arm-unkown-linux-gnueabi toolchain. However, crosstool-ng makes compiling toolchains quite straight forward and makes customization possible if required.

First specify the crosstools-ng version and some build directories. The final toolchain is built to ~/x-tools by default.

CROSSTOOL_VERSION=1.22.0
BASEDIR=~/arm-tool-chain
CROSS_TOOL_HOME=$BASDIR/crosstool/source/
CROSS_TOOL_PREFIX=$BASDIR/crosstool/bin/
TOOLCHAIN_HOME=$BASDIR/toolchain/

Make the directories used to build the cross-compiler.

mkdir -p $CROSS_TOOL_HOME
mkdir -p $CROSS_TOOL_PREFIX
mkdir -p $TOOLCHAIN_HOME

Downloading, verifying and building crosstools-ng should be no problem in sane build environment. I have found that I sometimes need to apply a minor patch to get the entire toolchain to build. So far these have not been too difficult to work out or find a patch for.

cd $CROSS_TOOL_HOME
wget http://crosstool-ng.org/download/crosstool-ng/crosstool-ng-$CROSSTOOL_VERSION.tar.bz2
tar xjf crosstool-ng-$CROSSTOOL_VERSION.tar.bz2

# The package signed with Bryan Hundven's gpg key, this can be verified by
# downloading the key are verifying the signature.
wget http://crosstool-ng.org/download/crosstool-ng/crosstool-ng-$CROSSTOOL_VERSION.tar.bz2.sig
gpg --recv-keys 35B871D1
gpg --verify crosstool-ng-$CROSSTOOL_VERSION.tar.bz3.sig


cd crosstool-ng

# I had to apply this patch to get the native gdb to compile,
# https://github.com/crosstool-ng/crosstool-ng/pull/273/files

./configure --prefix=$CROSS_TOOL_PREFIX
make
make install
PATH="${PATH}:$CROSS_TOOL_PREFIX/bin"

In this case configuring the toolchain is as simple as selecting a predefined sample. In other cases crosstool-ng has a Linux kernel like menuconfig command to browse and update settings.

cd $TOOLCHAIN_HOME
ct-ng arm-unknown-linux-gnueabi

# If you want to further configure the build, I didn't make any changes here,
# but if your target has hardware floating point support for example you might
# want to enable it here.
#   ct-ng menuconfig

ct-ng build

If all works out well, the tools and libraries should have been built to ~/x-tools/arm-unknown-linux-gnueabi/.

$ ls -1a ~/x-tools/arm-unknown-linux-gnueabi/bin/
.
..
arm-unknown-linux-gnueabi-addr2line
arm-unknown-linux-gnueabi-ar
arm-unknown-linux-gnueabi-as
arm-unknown-linux-gnueabi-c++
arm-unknown-linux-gnueabi-cc
arm-unknown-linux-gnueabi-c++filt
arm-unknown-linux-gnueabi-cpp
arm-unknown-linux-gnueabi-ct-ng.config
arm-unknown-linux-gnueabi-dwp
arm-unknown-linux-gnueabi-elfedit
arm-unknown-linux-gnueabi-g++
arm-unknown-linux-gnueabi-gcc
arm-unknown-linux-gnueabi-gcc-5.2.0
arm-unknown-linux-gnueabi-gcc-ar
arm-unknown-linux-gnueabi-gcc-nm
arm-unknown-linux-gnueabi-gcc-ranlib
arm-unknown-linux-gnueabi-gcov
arm-unknown-linux-gnueabi-gcov-tool
arm-unknown-linux-gnueabi-gdb
arm-unknown-linux-gnueabi-gprof
arm-unknown-linux-gnueabi-ld
arm-unknown-linux-gnueabi-ld.bfd
arm-unknown-linux-gnueabi-ldd
arm-unknown-linux-gnueabi-ld.gold
arm-unknown-linux-gnueabi-nm
arm-unknown-linux-gnueabi-objcopy
arm-unknown-linux-gnueabi-objdump
arm-unknown-linux-gnueabi-populate
arm-unknown-linux-gnueabi-ranlib
arm-unknown-linux-gnueabi-readelf
arm-unknown-linux-gnueabi-size
arm-unknown-linux-gnueabi-strings
arm-unknown-linux-gnueabi-strip

We should add this to our path if we want to use them:

PATH=$PATH:~/x-tools/arm-unknown-linux-gnueabi/

The -v option will tell us a little about the toolchain:

$ arm-unknown-linux-gnueabi-gcc -v
Using built-in specs.
COLLECT_GCC=arm-unknown-linux-gnueabi-gcc
COLLECT_LTO_WRAPPER=/home/dev/x-tools/arm-unknown-linux-gnueabi/libexec/gcc/arm-unknown-linux-gnueabi/5.2.0/lto-wrapper
Target: arm-unknown-linux-gnueabi
Configured with:
/home/dev/projects/arm-tool-chain/build/bin/.build/src/gcc-5.2.0/configure
--build=x86_64-build_pc-linux-gnu --host=x86_64-build_pc-linux-gnu
--target=arm-unknown-linux-gnueabi
--prefix=/home/dev/x-tools/arm-unknown-linux-gnueabi
--with-sysroot=/home/dev/x-tools/arm-unknown-linux-gnueabi/arm-unknown-linux-gnueabi/sysroot
--enable-languages=c,c++ --with-float=soft --with-pkgversion='crosstool-NG crosstool-ng-1.22.0' --disable-sjlj-exceptions --enable-__cxa_atexit
--disable-libmudflap --disable-libgomp --disable-libssp
--disable-libquadmath --disable-libquadmath-support --disable-libsanitizer
--with-gmp=/home/dev/projects/arm-tool-chain/build/bin/.build/arm-unknown-linux-gnueabi/buildtools
--with-mpfr=/home/dev/projects/arm-tool-chain/build/bin/.build/arm-unknown-linux-gnueabi/buildtools
--with-mpc=/home/dev/projects/arm-tool-chain/build/bin/.build/arm-unknown-linux-gnueabi/buildtools
--with-isl=/home/dev/projects/arm-tool-chain/build/bin/.build/arm-unknown-linux-gnueabi/buildtools
--with-cloog=/home/dev/projects/arm-tool-chain/build/bin/.build/arm-unknown-linux-gnueabi/buildtools
--with-libelf=/home/dev/projects/arm-tool-chain/build/bin/.build/arm-unknown-linux-gnueabi/buildtools
--enable-lto --with-host-libstdcxx='-static-libgcc -Wl,-Bstatic,-lstdc++,-Bdynamic -lm' --enable-threads=posix
--enable-target-optspace --enable-plugin --enable-gold --disable-nls
--disable-multilib
--with-local-prefix=/home/dev/x-tools/arm-unknown-linux-gnueabi/arm-unknown-linux-gnueabi/sysroot
--enable-long-long
Thread model: posix
gcc version 5.2.0 (crosstool-NG crosstool-ng-1.22.0)

We can also try using it to build something simple:

$ cd /tmp
$ cat > ./etc/init.d/rcS << EOF
#include 

int main (void) {
    printf ("Hello, ARM!\n");
    return 0;
}
EOF
$ arm-unknown-linux-gnueabi-gcc hello.c -o hello

Obviously we can't run it on the host as it is compiled for an ARM system:

$ ./hello
bash: ./hello: cannot execute binary file: Exec format error

We can get a bit of information about the binary using the file command:

$ file hello
hello: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.3, for GNU/Linux 4.3.0, not stripped

We can get a lot more information using the readelf (some of the output removed for verbosity):

$ arm-unknown-linux-gnueabi-readelf -a hello
ELF Header:
  Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00
  Class:                             ELF32
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              EXEC (Executable file)
  Machine:                           ARM
  Version:                           0x1
  Entry point address:               0x102c8
  Start of program headers:          52 (bytes into file)
  Start of section headers:          4676 (bytes into file)
  Flags:                             0x5000202, has entry point, Version5 EABI, soft-float ABI
  Size of this header:               52 (bytes)
  Size of program headers:           32 (bytes)
  Number of program headers:         8
  Size of section headers:           40 (bytes)
  Number of section headers:         29
  Section header string table index: 26

..

Program Headers:
  Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
  EXIDX          0x0004a4 0x000104a4 0x000104a4 0x00008 0x00008 R   0x4
  PHDR           0x000034 0x00010034 0x00010034 0x00100 0x00100 R E 0x4
  INTERP         0x000134 0x00010134 0x00010134 0x00013 0x00013 R   0x1
      [Requesting program interpreter: /lib/ld-linux.so.3]
  LOAD           0x000000 0x00010000 0x00010000 0x004b0 0x004b0 R E 0x10000
  LOAD           0x0004b0 0x000204b0 0x000204b0 0x0011c 0x00120 RW  0x10000
  DYNAMIC        0x0004bc 0x000204bc 0x000204bc 0x000e8 0x000e8 RW  0x4
  NOTE           0x000148 0x00010148 0x00010148 0x00020 0x00020 R   0x4
  GNU_STACK      0x000000 0x00000000 0x00000000 0x00000 0x00000 RW  0x10

..

Dynamic section at offset 0x4bc contains 24 entries:
  Tag        Type                         Name/Value
 0x00000001 (NEEDED)                     Shared library: [libc.so.6]

..

Amongst the information here we can see that it links to the /lib/ld-linux.so.3 and libc.so.6 and shared libraries. These libraries were built with the cross-compiler and will need to be present in the /lib directory on the target system.

$ ls -1a ~/x-tools/arm-unknown-linux-gnueabi/arm-unknown-linux-gnueabi/sysroot/lib
.
..
ld-2.22.so
ld-linux.so.3
libanl-2.22.so
libanl.so.1
libatomic.a
libatomic.so
libatomic.so.1
libatomic.so.1.1.0
libBrokenLocale-2.22.so
libBrokenLocale.so.1
libc-2.22.so
libcrypt-2.22.so
libcrypt.so.1
libc.so.6
libdl-2.22.so
libdl.so.2
libgcc_s.so
libgcc_s.so.1
libitm.a
libitm.so
libitm.so.1
libitm.so.1.0.0
libitm.spec
libm-2.22.so
libmemusage.so
libm.so.6
libnsl-2.22.so
libnsl.so.1
libnss_compat-2.22.so
libnss_compat.so.2
libnss_db-2.22.so
libnss_db.so.2
libnss_dns-2.22.so
libnss_dns.so.2
libnss_files-2.22.so
libnss_files.so.2
libnss_hesiod-2.22.so
libnss_hesiod.so.2
libnss_nis-2.22.so
libnss_nisplus-2.22.so
libnss_nisplus.so.2
libnss_nis.so.2
libpcprofile.so
libpthread-2.22.so
libpthread.so.0
libresolv-2.22.so
libresolv.so.2
librt-2.22.so
librt.so.1
libSegFault.so
libstdc++.a
libstdc++.so
libstdc++.so.6
libstdc++.so.6.0.21
libstdc++.so.6.0.21-gdb.py
libsupc++.a
libthread_db-1.0.so
libthread_db.so.1
libutil-2.22.so
libutil.so.1

In a follow up post I write about using this cross compiler toolchain to compile a Linux kernel and Busybox and then run them in the qemu emulator.

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