Embedded Artistry's libc is a stripped-down C standard library implementation targeted for microcontroller-based embedded systems.
In order to conserve precious memory resources, this library does not supply the complete C standard library implementation. Instead, a subset of functions which are useful on bare-metal embedded systems has been selected. If you have a bare metal or RTOS-based embedded system, this library is for you!
Unlike many other C libraries that I've come across, this library implements unit tests and has addressed long-standing flaws in open-source implementations of the C standard library functions. We're continually adding tests and making additional improvements over the baseline implementations.
malloc and free are not included in this library. If you need dynamic memory allocation support, you will need to couple this library with something like Embedded Artistry's libmemory, which contains implementations of malloc and free.
If you are interested in contributing to this project, please read the CONTRIBUTING guide.
Embedded Artistry's libc is intended to provide a portable set of useful C standard library functions that allows quick bring-up of new bare-metal and RTOS-based embedded systems.
Additionally, we want to provide a high-quality libc implementation by ensuring that each function has unit test coverage and addresses flaws exposed by the static analyzer. Many C library function implementations remain untested and contain errors. We are fighting back against poor implementations.
In order to conserve memory, this library does not supply the complete C standard library functionality. Instead, a subset of functions which are useful on bare-metal embedded systems has been selected. This selection has primarily been driven by my own experience in microcontroller-focused development. If you need additional features, please file an issue and make a feature request.
The functional implementations in this library have been selected for portability and quick bring-up of new systems. There may be more efficient implementations for these functions, but often they are architecture specific implementations. If you have suggestions for improving performance, we are always happy to hear them.
malloc and free are not included in this library. Because memory allocation schemes vary greatly with embedded systems (some not even allowing dynamic memory), you will need to supply your own implementations based on your system's needs. You can couple this library with the Embedded Artistry libmemory, which contains implementations of malloc and free.
This library provides a complete-enough implementation to compile and link clang's libc++ and libc++abi (see Embedded Artistry's libcpp project). In order to achieve this, some functions are only defined in the headers but do not have an implementation. Unsupported-but-defined functions can be removed using a build option (hide-unimplemented-libc-apis).
The following portions of the C library have been implemented:
assertcrt.c, exit, atexit, etc.)atoXabs, labs, llabsbsearchcallocdiv, ldiv, lldivheapsort, heapsort_rimaxabs, imaxdivqsort, qsort_rrand familyreallocstrtoX functions (many via gdtoa)printf family (most via embeddedartistry/printf, based on eyalroz/printf and originally mpaland/printf)putcharputstime types and asctime()wchar type definitions and wctype functionsIn addition, this library provides implementations for __stack_chk_guard and __stack_chk_fail.
The following architectures are currently supported:
The following unit tests need to be added:
reallocrand familyThese are not implemented by may be added in the future:
wchar functionserrno support (enabled as a compile-time switch)getopt supporttime supportFILE and additional stdio functionsWe are currently not planning full support for:
localeThis project uses Embedded Artistry's standard Meson build system, and dependencies are described in detail on our website.
At a minimum you will need:
git-lfs, which is used to store binary files in this repositoryThis project stores some files using git-lfs.
To install git-lfs on Linux:
sudo apt install git-lfsTo install git-lfs on MacOS:
brew install git-lfsAdditional installation instructions can be found on the git-lfs website.
The Meson build system depends on python3 and ninja-build.
To install on Linux:
sudo apt-get install python3 python3-pip ninja-buildTo install on OSX:
brew install python3 ninjaMeson can be installed through pip3:
pip3 install mesonIf you want to install Meson globally on Linux, use:
sudo -H pip3 install mesonThis project uses git-lfs, so please install it before cloning. If you cloned prior to installing git-lfs, simply run git lfs pull after installation.
This project is hosted on GitHub. You can clone the project directly using this command:
git clone --recursive git@github.com:embeddedartistry/libc.gitIf you don't clone recursively, be sure to run the following command in the repository or your build will fail:
git submodule update --initIf Make is installed, the library can be built by issuing the following command:
makeThis will build all targets for your current architecture.
You can clean builds using:
make cleanYou can eliminate the generated buildresults folder using:
make distcleanYou can also use meson directly for compiling.
Create a build output folder:
meson buildresultsAnd build all targets by running
ninja -C buildresultsCross-compilation is handled using meson cross files. Example files are included in the build/cross folder. You can write your own cross files for your specific processor by defining the toolchain, compilation flags, and linker flags. These settings will be used to compile libc. (or open an issue and we can help you).
Cross-compilation must be configured using the meson command when creating the build output folder. For example:
meson buildresults --cross-file build/cross/gcc_arm_cortex-m4.txtFollowing that, you can run make (at the project root) or ninja to build the project.
Tests will not be cross-compiled. They will only be built for the native platform.
Full instructions for building the project, using alternate toolchains, and running supporting tooling are documented in Embedded Artistry's Standardized Meson Build System on our website.
Position Independent Code (PIC) is enabled by default, but can be disabled during the Meson configuration stage by setting the built-in option b_staticpic to false:
meson buildresults -Db_staticpic=falseLink-time Optimization (LTO) can be enabled during the meson configuration stage by setting the built-in option b_lto to true:
meson buildresults -Db_lto=trueThis can be combined with other build options.
If you don't use meson for your project, the best method to use this project is to build it separately and copy the headers and library contents into your source tree.
include/ directory contents into your source tree.buildresults/src folderExample linker flags:
-Lpath/to/libc.a -lcIf you're using meson, you can use libc as a subproject. Place it into your subproject directory of choice and add a subproject statement:
libc = subproject('libc')You will need to promote the desired subproject dependency variable to your project:
libc_dep = libc.get_variable('libc_dep')You can use the dependency for your target library configuration in your executable declarations(s) or other dependencies. For example:
fwdemo_sim_platform_dep = declare_dependency(
include_directories: fwdemo_sim_platform_inc,
dependencies: [
fwdemo_simulator_hw_platform_dep,
posix_os_dep,
libmemory_native_dep,
libc_dep, # <----- libc added here
libcxxabi_native_dep,
libcxx_full_native_dep,
logging_subsystem_dep
],
sources: files('platform.cpp'),
)The tests for this library are written with CMocka, which is included as a subproject and does not need to be installed on your system. You can run the tests by issuing the following command:
make testBy default, test results are generated for use by the CI server and are formatted in JUnit XML. The test results XML files can be found in buildresults/test/.
The following meson project options can be set for this library when creating the build results directory with meson, or by using meson configure:
enable-pedantic: Turn on pedantic warningsenable-pedantic-error: Turn on pedantic warnings and errorshide-unimplemented-libc-apis: Hides the header definitions for functions which are not actually implementedenable-gnu-extensions will enable GNU libc extensions that are implemented in this librarydisable-builtins will tell the compiler not to generate built-in functions, forcing it to use the library functionsdisable-stack-protection will tell the compiler not to insert stack protection callsstack-canary-value enables you to customize the canary value for your application. Supply a hexadecimal string (e.g., '0xdeadbeef') with the same length as your processor's word size.disable-stk-guard-runtime-config disables the code that is used to configure __stk_chk_guard during program initialization. When this option is true, the program will revert to using a hard-coded definition for the guard value.Options can be specified using -D and the option name:
meson buildresults -Ddisable-builtins=falseThe same style works with meson configure:
cd buildresults
meson configure -Ddisable-builtins=falseThis library provides an implementation of __stack_chk_guard and __stack_chk_fail, which enables it to be used with GCC and Clang's stack protection code.
The default value for __stack_chk_guard can be overridden with the stack-canary-value build option.
[Documentation for the latest release can always be found here]https://embeddedartistry.github.io/libc/index.html.
Documentation can be built locally by running the following command:
make docsDocumentation can be found in buildresults/docs, and the root page is index.html.
If you need further assistance or have any questions, please file a GitHub Issue or send us an email using the Embedded Artistry Contact Form.
You can also reach out on Twitter: mbeddedartistry.
If you are interested in contributing to this project, please read our contributing guidelines.
Copyright © 2022 Embedded Artistry LLC
This project is licensed under the MIT License - see LICENSE file for details.
For other open-source licenses, please see the Software Inventory.
I'd like to thank the following individuals for their direct contributions on this project:
printf library)printf library and continued development)Many of the open-source function implementations used in this library have been pulled from two primary sources:
I have also used and improved the open-source gdtoa library.
The initial groundwork of testing was implemented by referencing the libc-test project.