Internally, crosstool-NG is script-based. To ease usage, the frontend is Makefile-based.

Makefile front-end

The entry point to crosstool-NG is the Makefile script ct-ng. Calling this script with an action will act exactly as if the Makefile was in the current working directory and make was called with the action as rule. Thus:

ct-ng menuconfig

is equivalent to having the Makefile in CWD, and calling:

make menuconfig

Having ct-ng as it is avoids copying the Makefile everywhere, and acts as a traditional command.

ct-ng loads sub- Makefiles from the library directory $(CT_LIB_DIR), as set up at configuration time with ./configure.

ct-ng also searches for config files, sub-tools, samples, scripts and patches in that library directory.

Because of a stupid make behavior/bug I was unable to track down, implicit make rules are disabled: installing with --local would trigger those rules, and mconf was unbuildable.

Kconfig parser

The kconfig language is a hacked version, vampirised from the Linux kernel, and (heavily) adapted to my needs.

The list of the most notable changes (at least the ones I remember) follows:

  • the CONFIG_ prefix has been replaced with CT_

  • a leading | in prompts is skipped, and subsequent leading spaces are not trimmed; otherwise leading spaces are silently trimmed

  • removed the warning about undefined environment variable

The kconfig parsers (conf and mconf) are not installed pre-built, but as source files. Thus you can have the directory where crosstool-NG is installed, exported (via NFS or whatever) and have clients with different architectures use the same crosstool-NG installation, and most notably, the same set of patches.

Architecture-specific

Note

this chapter is not really well written, and might thus be a little bit complex to understand. To get a better grasp of what an architecture is, the reader is kindly encouraged to look at the arch/ sub-directory, and to the existing architectures to see how things are laid out.

An architecture is defined by:

  • a human-readable name, in lower case letters, with numbers as appropriate; underscore is allowed; space and special characters are not, e.g.:

    arm
    x86_64
    
  • a file in config/arch/, named after the architecture’s name, and suffixed with .in, e.g.:

    config/arch/arm.in
    
  • a file in scripts/build/arch/, named after the architecture’s name, and suffixed with .sh, e.g.:

    scripts/build/arch/arm.sh
    

The architecture’s .in file API

Note

Here, and in the following, %arch% is to be replaced with the actual architecture name.

The ARCH_%arch% option

This config option must have neither a type, nor a prompt! Also, it can not depend on any other config option.

EXPERIMENTAL is managed as in kernel options ?.

A (terse) help entry must be defined for this architecture, e.g.,

config ARCH_arm
  help
    The ARM architecture.

Adequate associated config options may be selected, e.g.,

config ARCH_arm
  select ARCH_SUPPORTS_BOTH_ENDIAN
  select ARCH_DEFAULT_LE
  help
    The ARM architecture.

Note

64-bit architectures shall select ARCH_64.

config ARCH_x86_64
   select ARCH_64
   help
     The x86_64 architecture.

Other target-specific options

At your discretion. Note however that to avoid name-clashing, such options shall be prefixed with ARCH_%arch%.

Note

Due to historical reasons, and lack of time to clean up the code, I may have left some config options that do not completely conform to this, as the architecture name was written all upper case. However, the prefix is unique among architectures, and does not cause harm).

The architecture’s .sh file API

  • the function CT_DoArchTupleValues

    • parameters: none

    • environment:

      • all variables from the .config file,

      • the two variables target_endian_eb and target_endian_el which are the endianness suffixes

    • return value: 0 upon success, !0 upon failure

    • provides:

      • environment variable CT_TARGET_ARCH (mandatory)

        • contains: the architecture part of the target tuple, e.g. armeb for big endian ARM, or i386 for an i386
      • environment variable CT_TARGET_SYS (optional)

        • contains: the system part of the target tuple, e.g., gnu for glibc on most architectures, or gnueabi for glibc on an ARM EABI

        • defaults to:

          • gnu for glibc-based toolchain

          • uclibc for uClibc-based toolchain

      • environment variables to configure the cross-gcc (defaults) (optional)

        gcc ./configure switch selects default
        CT_ARCH_WITH_ARCH architecture level --with-arch=${CT_ARCH_ARCH}
        CT_ARCH_WITH_ABI ABI level --with-abi=${CT_ARCH_ABI}
        CT_ARCH_WITH_CPU CPU instruction set --with-cpu=${CT_ARCH_CPU}
        CT_ARCH_WITH_TUNE scheduling --with-tune=${CT_ARCH_TUNE}
        CT_ARCH_WITH_FPU FPU type --with-fpu=${CT_ARCH_FPU}
        CT_ARCH_WITH_FLOAT floating point arithm. --with-float=soft or [empty]
      • environment variables to pass to the cross-gcc to build target binaries (defaults) (optional)

        gcc ./configure switch selects default
        CT_ARCH_ARCH_CFLAG architecture level -march=${CT_ARCH_ARCH}
        CT_ARCH_ABI_CFLAG ABI level -mabi=${CT_ARCH_ABI}
        CT_ARCH_CPU_CFLAG CPU instruction set -mcpu=${CT_ARCH_CPU}
        CT_ARCH_TUNE_CFLAG scheduling -mtune=${CT_ARCH_TUNE}
        CT_ARCH_FPU_CFLAG FPU type -mfpu=${CT_ARCH_FPU}
        CT_ARCH_FLOAT_CFLAG floating point arithm. -msoft-float or [empty]
        CT_ARCH_ENDIAN_CFLAG big or little endian -mbig-endian or -mlittle-endian
      • the environment variables to configure the core and final compiler, specific to this architecture (optional):

        • CT_ARCH_CC_CORE_EXTRA_CONFIG: additional, architecture specific core gcc ./configure flags

        • CT_ARCH_CC_EXTRA_CONFIG: additional, architecture specific final gcc ./configure flags

        • default to: all empty

      • the architecture-specific CFLAGS and LDFLAGS (optional):

        • CT_ARCH_TARGET_CLFAGS

        • CT_ARCH_TARGET_LDFLAGS

        • default to: all empty

You can have a look at config/arch/arm.in and scripts/build/arch/arm.sh for a quite complete example of what an actual architecture description looks like.

Kernel specific

A kernel is defined by:

  • a human-readable name, in lower case letters, with numbers as appropriate; underscore is allowed, space and special characters are not (although they are internally replaced with underscores); e.g.:

    linux
    bare-metal
    
  • a file in config/kernel/, named after the kernel name, and suffixed with .in, e.g.:

    config/kernel/linux.in
    config/kernel/bare-metal.in
    
  • a file in scripts/build/kernel/, named after the kernel name, and suffixed with .sh, e.g.:

    scripts/build/kernel/linux.sh
    scripts/build/kernel/bare-metal.sh
    

The kernel’s .in file must contain:

  • an optional line containing exactly # EXPERIMENTAL, starting on the first column, and without any following space or other character.

    If this line is present, then this kernel is considered EXPERIMENTAL, and correct dependency on EXPERIMENTAL will be set.

  • the config option KERNEL_%kernel_name% (where %kernel_name% is to be replaced with the actual kernel name, with all special characters and spaces replaced by underscores), e.g.:

    KERNEL_linux
    KERNEL_bare_metal
    

    This config option must have neither a type, nor a prompt! Also, it can not depends on EXPERIMENTAL.

    A (terse) help entry for this kernel must be defined, e.g.:

    config KERNEL_bare_metal
      help
        Build a compiler for use without any kernel.
    

    Adequate associated config options may be selected, e.g.:

    config KERNEL_bare_metal
      select BARE_METAL
      help
        Build a compiler for use without any kernel.
    
  • other kernel specific options, at your discretion. Note however that, to avoid name-clashing, such options should be prefixed with KERNEL_%kernel_name%, where %kernel_name% is again to be replaced with the actual kernel name.

Note

Due to historical reasons, and lack of time to clean up the code, Yann may have left some config options that do not completely conform to this, as the kernel name was written all upper case. However, the prefix is unique among kernels, and does not cause harm).

The kernel’s .sh file API:

  • is a bash script fragment

  • defines function CT_DoKernelTupleValues

    • see the architecture’s CT_DoArchTupleValues, except for: [FIXME?]

    • set the environment variable CT_TARGET_KERNEL, the kernel part of the target tuple

    • return value: ignored

  • defines function do_kernel_get:

    • parameters: none

    • environment:

      • all variables from the .config file.
    • return value: 0 for success, !0 for failure.

    • behavior: download the kernel’s sources, and store the tarball into ${CT_TARBALLS_DIR}. To this end, a function is available that abstracts downloading tarballs:

      • CT_DoGet <tarball_base_name> <URL1 [URL...]>, e.g.:

        CT_DoGet linux-2.6.26.5 ftp://ftp.kernel.org/pub/linux/kernel/v2.6
        

        Note

        Retrieving sources from SVN, CVS, git and the likes is not supported by CT_DoGet. You’ll have to do this by hand, as it is done for eglibc in scripts/build/libc/eglibc.sh.

  • defines function do_kernel_extract:

    • parameters: none

    • environment:

      • all variables from the .config file,
    • return value: 0 for success, !0 for failure.

    • behavior: extract the kernel’s tarball into ${CT_SRC_DIR}, and apply required patches. To this end, a function is available that abstracts extracting tarballs:

      • CT_ExtractAndPatch <tarball_base_name>, e.g.:

        CT_ExtractAndPatch linux-2.6.26.5
        
  • defines function do_kernel_headers:

    • parameters: none

    • environment:

      • all variables from the .config file,
    • return value: 0 for success, !0 for failure.

    • behavior: install the kernel headers (if any) in ${CT_SYSROOT_DIR}/usr/include

  • defines any kernel-specific helper functions

    These functions, if any, must be prefixed with do_kernel_%CT_KERNEL%_, where %CT_KERNEL% is to be replaced with the actual kernel name, to avoid any name-clashing.

You can have a look at config/kernel/linux.in and scripts/build/kernel/linux.sh as an example of what a complex kernel description looks like.

Adding a new version of a component

When a new component, such as the Linux kernel, gcc or any other is released, adding the new version to crosstool-NG is quite easy. There is a script that will do all that for you:

scripts/addToolVersion.sh

Run it with no option to get some help.

Build scripts

[To Be Written later…]