An Arm cross compiler toolchain allows developers to compile code for Arm-based devices on a host system with a different architecture, like x86. It provides the necessary tools to build applications targeting Arm processors from a non-Arm development machine.
Why use a cross compiler?
Developing natively on an Arm device can be challenging due to limited resources and lack of development tools. A cross compiler allows compiling on a more powerful host machine with abundant resources. Additional benefits include:
- Faster compilation times by leveraging the host’s performance
- Use the same toolchain on different host platforms like Linux, Windows, macOS
- Develop without requiring physical access to the target Arm device
- Supports building for multiple Arm architectures from one toolchain
Components of an Arm cross compiler
An Arm cross compiler toolchain typically contains:
- Compiler: Converts source code like C/C++ into Arm machine code
- Assembler: Converts assembly language into machine code
- Linker: Combines object files into executables
- Archiver: Manages libraries of object code
- Debugger: Debugs source code and examines program execution
- Utilities: Additional tools like make, simulators, optimizers etc.
Compiler
The compiler like arm-none-eabi-gcc is the heart of the toolchain. It performs compilation of source files into object files containing Arm machine code. Important compiler operations include:
- Preprocessing – Expands macros and headers
- Parsing – Checks for correct syntax
- Semantic analysis – Contextual analysis for consistency
- Intermediate code generation – SImpler representation for optimization
- Machine code generation – Converts to target architecture opcodes
- Assembly/object file generation – Assembler format or object file
Assembler
The assembler like arm-none-eabi-as converts hand-written assembly language files into machine code object files. It is used when developers want low-level control over software.
Linker
The linker like arm-none-eabi-ld combines multiple object files into a single executable file. It resolves references between object files and libraries.
Archiver
The archiver like arm-none-eabi-ar is used to create static libraries from multiple object files. This allows reusable code modules to be linked into programs.
Debugger
The debugger like arm-none-eabi-gdb is used to test and debug programs. It allows stepping through code, setting breakpoints, examining variables and registers, etc.
Bare metal vs OS toolchains
Arm cross compiler toolchains are offered in two main variants:
- Bare metal – Used when compiling code running directly on hardware without OS. Requires just a C/C++ runtime library.
- OS – Used for compiling code running on an OS like Linux. Links code against OS libraries.
Acquiring an Arm cross compiler
There are several options for obtaining an Arm cross compiler toolchain:
- GNU Arm Embedded Toolchain – Free toolchain from Arm’s GNU toolchain project with GCC, GDB etc.
- Arm Compiler – Arm’s commercial compiler toolchain with advanced optimizations.
- Build from source – Manually building GCC, binutils, debugger, libraries etc.
- Vendor toolchains – Toolchains offered by silicon partners, OEMs, OS vendors etc.
GNU Arm Embedded Toolchain
The GNU Arm Embedded Toolchain is a free, open source cross compiler offered by Arm’s GNU toolchain project. It supports bare metal and OS development for Arm Cortex-A, Cortex-R and Cortex-M series processors. Available for Windows, Linux and macOS hosts.
Arm Compiler
Arm Compiler is Arm’s commercial cross compiler toolchain designed for high performance. Includes Clang-based compiler, assembler, linker, debugger, analyzer and libraries. Supports advanced optimizations and has a small code footprint. Free trials available.
Build from source
Developers can build a custom cross compiler by compiling GCC, binutils, debugger, C library, etc from source code. Allows customizing the toolchain but requires expertise. Build scripts like Crosstool-NG help automate the process.
Vendor toolchains
Many Arm ecosystem partners offer their own branded cross compiler toolchains. Silicon vendors often provide toolchains optimized and certified for their chips. OS vendors like Linux provide cross compilers for targeting their OS. These toolchains integrate vendor-specific optimizations and libraries.
Using the Arm cross compiler
Once an Arm cross compiler is installed, developers can use it to build Arm applications on their host system. Here are some examples of usage:
Compiling C/C++ code
$ arm-none-eabi-gcc -c code.c -o code.o $ arm-none-eabi-gcc code.o -o code
Assembling ARM assembly
$ arm-none-eabi-as assembly.s -o assembly.o
Linking object files
$ arm-none-eabi-ld code.o utils.o -o app
Creating a library
$ arm-none-eabi-ar rcs libutils.a utils.o
Debugging an app
$ arm-none-eabi-gdb app (gdb) …
The cross compiler prefix identifies each tool in the toolchain. Flags and arguments are used to control compilation, assembly, linking etc. The produced Arm binary can then be deployed to a target device.
Conclusion
An Arm cross compiler toolchain enables efficiently developing Arm applications on non-Arm host systems. Using a cross compiler provides performance and flexibility advantages versus native Arm development. Both open source and commercial toolchain options are available from Arm and ecosystem partners.
Learning to use an Arm cross compiler is a key skill for embedded and IoT developers working with the Arm architecture. With a proper cross compiler set up, developers can maximize productivity when targeting the popular Arm family of processors and cores.
