I am working on an STM32F4 project with code generated by STM32CubeMX. In order to add some Rust to my project, I have ported the Makefile to CMake and am then using Corrosion to build and link a Rust project as a static library. This has worked surprisingly well up until the point I tried adding FreeRTOS to the project. For some reason, trying to enter a delay after doing memory allocation on the Rust side causes the chip to HardFault. Looking at the status registers, it appears this is being caused by a INVSTATE UsageFault. Unfortunately, the LR pushed to the stack doesn't seem to point to an actual location at this point, so I have no idea what instruction is causing the problem.
The description for this type of error at https://interrupt.memfault.com/blog/cortex-m-hardfault-debug claims "If this rule is violated, a INVSTATE exception will be generated. When writing C code, the compiler will take care of this automatically, but this is a common bug which can arise when hand-writing assembly.". Could it possibly be that something is getting messed up between the C and Rust compilers?
P.S. Rust is using a custom global allocator powered by pvPortMalloc and vPortFree and this seems to work just fine.
It turns out the problem had nothing to do with the interop between the languages. It was simply that the stack size for the FreeRTOS thread was not large enough.