Let’s start with the background of newlib. It is an open-source C standard library (libc) that originated from Cygnus and was later maintained by Red Hat. Unlike the “heavyweights” like glibc, newlib is specifically designed for bare-metal and small systems, allowing it to run without an operating system. In simple terms, it provides you with a portable, customizable, and lightweight C library without the need to bring the entire Linux environment along.
What makes it so impressive? You may have encountered various C libraries, and the biggest issues are usually portability and size. The advantages of newlib are: first, it is extremely portable— the low-level system call (syscall) interfaces are left for you to implement, such as read/write and memory allocation, all of which you need to write yourself. Second, the size is controllable; you can opt for the “newlib-nano” slim version, which removes fancy features like locale and file system caching, directly freeing up space for your program. Third, the community is active; newlib support is included in the GCC cross-compilation toolchain, and with a simple configuration, you can use it, saving a lot of time avoiding pitfalls.
How to use it in embedded systems?
- 1. When setting up the cross-compilation toolchain, use the
<span>--with-newlib</span>option to enable GCC to work with newlib. - 2. Provide a set of syscall functions in your project:
<span>_write</span>,<span>_read</span>,<span>_sbrk</span>, and other basic interfaces. A common practice is to redirect<span>_write</span>to UART and point<span>sbrk</span>to the heap area, allowing malloc/free to be used. - 3. If you are using MCUs like STM32 or ESP32, many examples directly redirect printf to the serial port, and you only need to implement
<span>fputc</span>to get it working. - 4. Add
<span>-lc -lgloss</span>(or the nano version<span>-lc_nano -lgloss</span>) during linking to allow newlib’s underlying library to “handshake” with your hardware calls.
sbrk and malloc: The Untold Secrets When it comes to memory allocation, newlib delegates the expansion of heap space to <span>sbrk</span>. This means that when malloc needs more space, it will call your implementation of <span>sbrk(int incr)</span>— you just need to reserve an address range in the linker script and let <span>sbrk</span> “dig” upwards. But be careful: if you dig too much, it may collide with the stack, leading to a crash if you’re not careful. So, remember to create a diagram in your project to leave enough “safety distance” between the heap and stack!
The Rest: Slimming Secrets of newlib-nano newlib-nano is the “lightweight brother” of newlib, primarily cutting out locale support, floating-point I/O, and complex formatting features. The size can be reduced even further, making it particularly suitable for scenarios where Flash and RAM are tight. To use it, simply change the GCC linking options to <span>-lc_nano</span> and add <span>--specs=nano.specs</span>. If you find it cumbersome, you can also manually disable macros like <span>_PRINTF_FLOAT</span> and <span>_SCANF_FLOAT</span> in the <span>.config</span> file for a more aggressive slimming.
A Small Case Study in Real Projects Without further ado, let me share a project I worked on with the STM32F407.
- • I used GCC + newlib-nano, and the entire firmware compiled to less than 200KB of Flash and < 40KB of RAM.
- • The
<span>_write</span>function uses HAL_UART_Transmit as the low-level implementation, making printf an instant “real-time debugging tool”. - • malloc/free can run stably under FreeRTOS, and combined with memory pools, tasks with moderate data volumes do not stall.
- • The best part is that when it comes time to port to ESP32, I only need to change sbrk and UART, and the rest of the code requires almost zero modification, saving time and effort.
Why You Should Give It a Try?
- • If you are still using those “weird C libraries that require you to write a ton of IO interfaces,” you are a bit outdated.
- • The documentation and community for newlib are comprehensive, so you don’t have to worry about getting no answers— after all, it is officially supported by GCC.
- • It can handle both large projects and small demos, with the library size and functional modularity at your discretion, maximizing flexibility.
Conclusion Overall, newlib is like a “Swiss Army Knife”— whether you are working with STM32, ESP, or RISC-V, if you want a customizable, easily portable, and community-supported C library, it will definitely come in handy. Stop wasting resources on large libraries; use newlib to make your embedded development easier, more flexible, and more efficient!
Project address: https://github.com/bminor/newlib