buildroot

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#

# toolchain-external

#

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​

#

# This package implements the support for external toolchains, i.e

# toolchains that are available pre-built, ready to use. Such toolchain

# may either be readily available on the Web (Linaro, Sourcery

# CodeBench, from processor vendors) or may be built with tools like

# Crosstool-NG or Buildroot itself. So far, we have tested this

# with:

#

#  * Toolchains generated by Crosstool-NG

#  * Toolchains generated by Buildroot

#  * Toolchains provided by Linaro for the ARM and AArch64

#    architectures

#  * Sourcery CodeBench toolchains (from Mentor Graphics) for the ARM,

#    MIPS, PowerPC, x86, x86_64 and NIOS 2 architectures. For the MIPS

#    toolchain, the -muclibc variant isn't supported yet, only the

#    default glibc-based variant is.

#  * Analog Devices toolchains for the Blackfin architecture

#  * Xilinx toolchains for the Microblaze architecture

#  * Synopsys DesignWare toolchains for ARC cores

#

# The basic principle is the following

#

#  1. If the toolchain is not pre-installed, download and extract it

#  in $(TOOLCHAIN_EXTERNAL_INSTALL_DIR). Otherwise,

#  $(TOOLCHAIN_EXTERNAL_INSTALL_DIR) points to were the toolchain has

#  already been installed by the user.

#

#  2. For all external toolchains, perform some checks on the

#  conformity between the toolchain configuration described in the

#  Buildroot menuconfig system, and the real configuration of the

#  external toolchain. This is for example important to make sure that

#  the Buildroot configuration system knows whether the toolchain

#  supports RPC, IPv6, locales, large files, etc. Unfortunately, these

#  things cannot be detected automatically, since the value of these

#  options (such as BR2_TOOLCHAIN_HAS_NATIVE_RPC) are needed at

#  configuration time because these options are used as dependencies

#  for other options. And at configuration time, we are not able to

#  retrieve the external toolchain configuration.

#

#  3. Copy the libraries needed at runtime to the target directory,

#  $(TARGET_DIR). Obviously, things such as the C library, the dynamic

#  loader and a few other utility libraries are needed if dynamic

#  applications are to be executed on the target system.

#

#  4. Copy the libraries and headers to the staging directory. This

#  will allow all further calls to gcc to be made using --sysroot

#  $(STAGING_DIR), which greatly simplifies the compilation of the

#  packages when using external toolchains. So in the end, only the

#  cross-compiler binaries remains external, all libraries and headers

#  are imported into the Buildroot tree.

#

#  5. Build a toolchain wrapper which executes the external toolchain

#  with a number of arguments (sysroot/march/mtune/..) hardcoded,

#  so we're sure the correct configuration is always used and the

#  toolchain behaves similar to an internal toolchain.

#  This toolchain wrapper and symlinks are installed into

#  $(HOST_DIR)/usr/bin like for the internal toolchains, and the rest