umm-malloc-rs

Provides a global allocator using the umm_malloc library.

umm_malloc is a small and simple memory allocator designed for embedded systems. It is able to allocate and free quickly with limited memory fragmentation.

Limitations

All allocations from this allocator are aligned by 8 bytes. Requesting a larger alignment is not implemented and will panic.

Features

• first-fit Use the first available block for allocation, rather than search for a better fit.

• init-if-uninitialized Adds checks to every malloc function which tries to initialize the heap (using the extern symbols for heap location) if it is not initialized.

• hang-if-uninitialized Adds checks to every malloc function which enters an infinite loop if the heap is not initialized.

• enable-pie Compiles the umm_malloc C code position independent (-fPIE). You'll likely want to enable it for rustc also e.g. -C relocation-model=pie.

Global Allocator Critical Sections

Concurrent access to the global allocator is Undefined Behavior. Enable one of the following cargo features to configure how access to the global allocator is controlled.

• cortex-m-interrupt-critical-section: interrupt-disabled critical section for ARM Cortex-M processors.
• extern-critical-section: Uses the extern functions void _umm_critical_entry(uint32_t*) and void _umm_critical_exit(uint32_t*) to implement the global allocator critical sections. You MUST supply those functions via some other means. Note that critical sections may nest.
• unsafe-no-critical-section: no critical sections around the global allocator. You MUST prevent concurrent use of the global allcator to avoid Undefined Behavior.

Future Work

umm_malloc has features for collecting metrics and detecting heap corruption, which could be exposed conveniently with cargo features.

An implementation of memalign could be added to umm_malloc.