Embedded Artistry libmemory

Embedded Artistry's libmemory is a memory management library for embedded systems. If you have a bare metal system and want to use malloc(), this library is for you!

libmemory provides various implementations of the malloc() and free() functions. The primary malloc implementation is a free-list allocator which can be used on a bare-metal system. Wrappers for some RTOSes are also provided (and can be added if not already). You will also find other useful memory functions, such as aligned_malloc().

This library is meant to be coupled with a libc implementation (such as the Embedded Artistry libc). malloc() and free() are not redefined in these headers, so you can safely use this library with your platform's existing libc.

Table of Contents

1. About the Project
2. Project Status
3. Getting Started
   1. Requirements
      1. git-lfs
      2. Meson Build System
   2. Getting the Source
   3. Building
   4. Installation
4. Configuration Options
5. Library Variants
   1. Native Targets
6. Usage
   1. Thread Safety
   2. Aligned malloc
7. Using a Custom Libc
8. Testing
9. Documentation
10. Need Help?
11. Contributing
12. Further Reading
13. Authors
14. License
15. Acknowledgments

About the Project

This library is meant to allow developers of embedded systems to utilize the malloc() and free() functions if their platform does not currently support it. The baseline malloc() implementation can be used without an RTOS or any other supporting software. Only a block of memory needs to be assigned.

Many RTOSes provide dynamic memory allocation functionality, but these functions are not typically called malloc() and free(). Wrappers can be provided for these RTOSes to improve code portability.

A block of memory needs to be initially assigned using the malloc_addblock() function. This tells the malloc implementation what memory address and size to use for the heap.

// Allocate 4MB to the heap starting at memory address 0xDEADBEEF
malloc_addblock(0xDEADBEEF, 4 * 1024 * 1024);

One memory has been allocated to the heap, you can use malloc() and free() as expected.

Project Status

• Basic memory allocation is implemented using the free-list strategy
• x86, x86_64, ARM, and ARM64 compilation is supported
• Example RTOS implementations are provided for FreeRTOS and ThreadX
• An implementation exists that can be used with the Embedded Virtual Machine framework
• Tests are currently in place for malloc(), free(), aligned_malloc(), and aligned_free()
• No test for overlapping memory blocks currently exists

Getting Started

Requirements

This 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 repository
• Meson is the build system
• Some kind of compiler for your target system.
  • This repository has been tested with:
    • gcc-7, gcc-8, gcc-9
    • arm-none-eabi-gcc
    • Apple clang
    • Mainline clang

git-lfs

This project stores some files using git-lfs.

To install git-lfs on Linux:

sudo apt install git-lfs

To install git-lfs on OS X:

brew install git-lfs

Additional installation instructions can be found on the git-lfs website.

Meson Build System

The Meson build system depends on python3 and ninja-build.

To install on Linux:

sudo apt-get install python3 python3-pip ninja-build

To install on OSX:

brew install python3 ninja

Meson can be installed through pip3:

pip3 install meson

If you want to install Meson globally on Linux, use:

sudo -H pip3 install meson

Getting the Source

This 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/libmemory.git

If you don't clone recursively, be sure to run the following command in the repository or your build will fail:

git submodule update --init

Building

If Make is installed, the library can be built by issuing the following command:

make

This will build all targets for your current architecture.

You can clean builds using:

make clean

You can eliminate the generated buildresults folder using:

make distclean

You can also use meson directly for compiling.

Create a build output folder:

meson buildresults

And build all targets by running

ninja -C buildresults

Cross-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.txt

Following 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.

Installation

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 desired library contents into your source tree.

• Copy the include/ directory contents into your source tree.
• Library artifacts are stored in the buildresults/src folder
• Copy the desired library to your project and add the library to your link step.

Example linker flags:

-Lpath/to/libmemory_freelist.a -lmemory_freelist

If you're using meson, you can use libmemory as a subproject. Place it into your subproject directory of choice and add a subproject statement:

libmemory = subproject('libmemory')

You will need to promote the subproject dependencies to your project in order to use them in your build targets:

libmemory = subproject('libmemory')

libmemory_native_dep = libmemory.get_variable('libmemory_native_dep')
libmemory_hosted_dep = libmemory.get_variable('libmemory_hosted_dep')
libmemory_freelist_dep = libmemory.get_variable('libmemory_freelist_dep')
libmemory_threadx_dep = libmemory.get_variable('libmemory_threadx_dep')
libmemory_freertos_dep = libmemory.get_variable('libmemory_freertos_dep')
libmemory_header_include =  libmemory.get_variable('libmemory_system_includes')
libmemory_framework_rtos_dep = libmemory.get_variable('libmemory_framework_rtos_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, # <----- libmemory dependency added here
		libc_native_dep, 
		libcxxabi_native_dep,
		libcxx_full_native_dep,
		logging_subsystem_dep
	],
	sources: files('platform.cpp'),
)

This will add the proper include paths, library targets, and build dependency rules to your application.

Configuration Options

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: Enable pedantic warnings
• enable-pedantic-error: Turn on pedantic warnings and errors
• use-libc-subproject: When true, use the subproject defined in the libc-subproject option. An alternate approach is to override c_stdlib in your cross files.
• libc-subproject: This array is used in combination with use-libc-subproject. The first entry is the subproject name. The second is the cross-compilation dependency to use. The third value is optional. If used, it is a native dependency to use with native library targets.

Options can be specified using -D and the option name:

meson buildresults -Denable-pedantic=true

The same style works with meson configure:

cd buildresults
meson configure -Denable-pedantic=true

Library Variants

This build provides a number of library variations. Many of these variants support different allocation strategies. Our recommended implementation for embedded systems without an RTOS is libmemory_freelist.`

• libmemory_assert
  • Calls to malloc/free will assert at runtime
  • This implementation is portable
• libmemory_freelist
  • Allocates memory from a freelist
  • Works with one or more blocks of memory
  • Memory must be initialized with malloc_addblock
  • The implementation can be made threadsafe by supplying implementations for malloc_lock and malloc_unlock in your application
  • This implementation is portable
• libmemory_freertos
  • Provides a sample FreeRTOS implementation that wraps the heap_5 FreeRTOS strategy
  • Memory must be initialized with malloc_addblock
  • Note that headers will need to be updated for your particular project prior to compilation (dependencies/rtos/freertos), or simply include the source code within your own project
• libmemory_threadx
  • Provides a sample ThreadX implementation that wraps the ThreadX memory allocators
  • Memory must be initialized with malloc_addblock
  • Note that headers will need to be updated for your particular project prior to compilation (dependencies/rtos/threadx), or simply include the source code within your own project

We also have variants that provide supplementary functions (e.g., aligned_malloc) without providing an implementation for malloc/free. This is primarily used for providing source code compatibility with systems that do provide a suitable malloc implementation (e.g., running a test program on your build machine).

• libmemory
  • Picks up extra libmemory functions but does not implement malloc/free
  • Will use an alternative libc implementation if specified malloc_addblock and malloc_init will assert at runtime
• libmemory_hosted
  • Picks up extra libmemory functions but does not implement malloc/free
  • Will use the compiler's libc implementation unless other specified flags override that setting (e.g., within your own build rules)
  • malloc_addblock and malloc_init will assert at runtime.

Native Targets

In addition, every library variant has a corresponding _native target. When cross-compilation builds are enabled, the target with the _native suffix will be compiled for your build machine, while the target without the suffix will be cross-compiled. This enables your application to use the appropriate variant for both cross-compilation targets and native: true targets (e.g., a unit test program or simulator application) in the same build.

Usage

A block of memory needs to be initially assigned using the malloc_addblock() function:

void malloc_addblock(void* addr, size_t size);

This tells the malloc implementation what memory address and size to use for the heap.

// Allocate 4MB to the heap starting at memory address 0xDEADBEEF
malloc_addblock(0xDEADBEEF, 4 * 1024 * 1024);

malloc() and free() will fail (return NULL) if no memory has been allocated. Once memory has been allocated to the heap, you can use malloc() and free() as expected.

Multiple blocks of memory can be added using malloc_addblock(). The memory blocks do not have to be contiguous.

Thread Safety

RTOS-based implementations are thread-safe depending on the RTOS and heap configuration.

The freelist implementation is not thread-safe by default. If you are using this version on a threaded system, you need to define two functions within your program:

void malloc_lock();
void malloc_unlock();

These should lock and unlock a mutex that is designed to protect malloc.

mutex_t malloc_mutex;

void malloc_lock() 
{
	mutex_lock(&malloc_mutex);
}

void malloc_unlock()
{
	mutex_unlock(&malloc_mutex);
}

These functions are defined as weakly linked in the library, so the default no-op condition will not be used if your functions is found by the linker. If you're doubtful that your calls are being included, check the disassembly for the functions - your version will not be no-ops!

Aligned malloc

You can allocate aligned memory using aligned_malloc():

void* aligned_malloc(size_t align, size_t size);

Alignment must be a power of two!

Aligned memory can only be free'd using aligned_free():

void aligned_free(void* ptr);

For more information, see aligned_memory.hand the documentation.

Using a Custom Libc

This project is designed to be used along with a libc implementation. If you are using this library, you may not be using the standard libc that ships with you compiler. This library needs to know about the particular libc implementation during its build, in case there are important differences in definitions.

There are two ways to tell this library about a libc:

1. Override c_stdlib in a cross-file, which will be automatically used when building this library.
2. Set use-libc-subproject to true
   1. By default, this will use the Embedded Artistry libc
   2. You can specify another Meson subproject by configuring libc-subproject. This is an array: the first value is the subproject name, the second the libc dependency variable, and the third is an optional native dependency that will be used with native library variants.

NOTE: External libc dependencies are only used for building the library. They are not forwarded through dependencies. You are expected to handle that with the rest of your program.

Testing

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 test

By 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/.

Documentation

Documentation for the latest release can always be found here.

Documentation can be built locally by running the following command:

make docs

Documentation can be found in buildresults/docs, and the root page is index.html.

Need help?

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.

Contributing

If you are interested in contributing to this project, please read our contributing guidelines.

Further Reading

• libmemory Documentation
• CONTRIBUTING guide

Authors

• Phillip Johnston - original library author - Embedded Artistry

License

Copyright (c) 2017 Embedded Artistry LLC

This project is licensed under the MIT License - see LICENSE file for details.

Acknowledgments

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