ARM GNU Toolchain

The ARM GNU toolchain refers to the suite of open source development tools used to build software that runs on ARM-based processors and systems. This includes things like compilers, debuggers, and other utilities for creating and optimizing code targeting the ARM architecture.

The most important components of the ARM GNU toolchain are:

• GNU Compiler Collection (GCC) – Contains the ARM compilers (arm-none-eabi-gcc, arm-linux-gnueabi-gcc, etc) used to compile code for ARM.
• GNU Binutils – Contains tools like the assembler (arm-none-eabi-as), linker (arm-none-eabi-ld), and other utilities for manipulating ARM binaries.
• GNU Debugger (GDB) – Debugging tool for ARM code.
• Newlib – C standard library implementation for embedded ARM systems.
• Glibc – C standard library for Linux-based ARM systems.

Obtaining the ARM Toolchain

There are a few ways to get the ARM GNU toolchain:

• Package Manager – Install a prebuilt toolchain package using your Linux distribution’s package manager (apt, yum, etc). Look for packages like gcc-arm-none-eabi, arm-linux-gnueabihf-toolchain, etc.
• SDK/IDE – Toolchains are often bundled with ARM development boards and vendor SDKs.
• Build from Source – Download and compile GCC, binutils, and other tools from source. More complex but offers customization.
• Prebuilt Toolchain – Download a pre-compiled toolchain like from ARM’s website or other third parties.

For most purposes, a prebuilt package or SDK toolchain is easiest. Building from source offers more customization if needed.

Toolchain Components

Some of the key components in the ARM GNU toolchain include:

Compilers

• arm-none-eabi-gcc – Compiler for bare-metal ARM C/C++ code.
• arm-linux-gnueabihf-gcc – Compiler for ARM Linux programs.
• arm-none-eabi-g++/arm-linux-gnueabihf-g++ – C++ support.
• arm-none-eabi-objc/arm-linux-gnueabihf-objc – Objective C compiler.

The compilers handle converting C/C++ code into ARM assembly/machine code. The “none-eabi” versions target bare-metal while “gnueabihf” targets ARM Linux systems.

Assemblers

• arm-none-eabi-as – Assembler for bare-metal ARM assembly code.
• arm-linux-gnueabihf-as – Assembler for Linux ARM systems.

Assemblers convert assembly language files into machine code object files.

Linker

• arm-none-eabi-ld – Bare-metal ARM linker.
• arm-linux-gnueabihf-ld – Linux ARM linker.

The linker combines object files and libraries into executables.

Debugger

arm-none-eabi-gdb/arm-linux-gnueabihf-gdb – GDB for debugging ARM programs.

Utilities

• objcopy – Convert between object file formats.
• objdump – Display information about object files.
• size – List object file section sizes.
• strings – Extract strings from binaries.
• strip – Remove symbols from object files.

Additional tools for manipulating binaries and analyzing compiled code.

Cross Compilation

A key feature of the ARM toolchain is support for cross compilation. This allows you to compile code for the ARM target platform on a host system with a different architecture like x86.

For example, you can run the ARM compilers on a Linux PC to generate binaries for an ARM Cortex-M microcontroller. The resulting code will run on the ARM target, even though it was compiled on the x86 host.

To cross compile:

1. Install the ARM toolchain for your host platform (Linux, Mac, Windows)
2. Specify the ARM target using compiler flags like -mcpu, -mfloat-abi, etc.
3. Link against the correct ARM C library (newlib, glibc, etc).
4. Copy the executable over to the target system.

With the proper cross compilation setup, the ARM GNU toolchain hides the complexity of generating code for the target ARM platform.

Common Tasks

Some common tasks with the ARM toolchain:

• Compile C/C++ code into ARM executables with arm-none-eabi-gcc or arm-linux-gnueabihf-gcc.
• Assemble ARM assembly source files with the arm-none-eabi-as or arm-linux-gnueabihf-as assemblers.
• Link object files and libraries into an executable using the arm-none-eabi-ld or arm-linux-gnueabihf-ld linkers.
• Debug ARM binaries with arm-none-eabi-gdb or arm-linux-gnueabihf-gdb.
• Analyze compiled ARM code with objdump, strings, size, etc.
• Strip unnecessary symbols from object files using the strip utility.
• Convert between binary formats with objcopy.

The toolchain provides everything needed to go from C/C++ source down to bare metal ARM executables.

Toolchain Options

The ARM toolchain has many options and flags for customizing the compilation process:

• -mcpu – Target a specific ARM core like cortex-m4, cortex-a53, etc.
• -march – Optimize for an ARM architecture version like armv7-a, armv8-m.main, etc.
• -mfpu – Floating point unit options like fpv4-sp-d16 for FPU architecture.
• -mfloat-abi – Calling convention used for passing floats.
• -mtune – Tune code for a specific ARM core without using all of its features.
• -mthumb – Generate 16-bit Thumb instruction set code.
• -mabi – Specify the ABI (application binary interface).

Plus many other specialized options for optimizing code size, enabling/disabling instructions, etc.

Supported ARM Architectures

The ARM GNU toolchain supports a wide range of ARM architectures including:

• ARMv6-M – Cortex-M0, M0+, M1 processors
• ARMv7-M – Cortex-M3, M4, M7
• ARMv7-A – Cortex-A5, A7, A8, A9, A15
• ARMv7-R – Cortex-R4, R5, R7, R8
• ARMv8-A – Cortex-A32, A35, A53, A55, A57, A72, A73
• ARMv8-M – Cortex-M23, M33
• ARMv8-R – Cortex-R52

Both 32-bit and 64-bit ARM cores are included, spanning microcontrollers to application processors.

Bare Metal vs Linux Toolchains

There are two main flavors of ARM toolchains:

• Bare metal – arm-none-eabi* tools target bare metal ARM Cortex-M microcontrollers.
• Linux – arm-linux-gnueabihf* tools target ARM Linux systems like boards running Linux.

Key differences:

• Bare metal uses newlib C library, Linux uses glibc.
• Linux toolchain supports threads, kernel integration, glibc features.
• Bare metal is fully static, Linux is dynamic and links to shared libraries (libc, pthreads, etc).

So choose the toolchain depending on if you are compiling for bare metal or Linux ARM targets.

Summary

In summary, the ARM GNU toolchain contains a robust set of open source tools for compiling, debugging, and analyzing code targeting ARM processors. Key components include the GCC compilers, binutils for assemblies/linking, GDB for debugging, and various utilities.

The toolchain supports cross compilation from hosts like x86 Linux to ARM targets. Both bare metal and Linux ARM platforms are covered by separate toolchain flavors. There are extensive options for optimizing performance for different ARM architectures.

Having a good ARM toolchain is critical for deeply understanding ARM systems and developing efficient software that fully leverages the capabilities of the ARM architecture.