zephyr: mempool implementation of GlobalAlloc

Allow a Rust app to bind the #[global_allocator] to a chosen Zephyr
mempool. This overrides the default of k_malloc in libstd, which allows
libstd and Box to work in user space.

Author: tylerwhall

rust-app/zephyr-sys/wrapper.h

@@ -4,6 +4,7 @@
 
 #include <rust_syscall_macros.h>
 #include <kernel.h>
+#include <misc/mempool.h>
 #include <device.h>
 #include <uart.h>
 

rust-app/zephyr/src/lib.rs

@@ -6,6 +6,7 @@ extern crate derive_more;
 
 pub mod device;
 pub mod kobj;
+pub mod mempool;
 pub mod mutex;
 pub mod semaphore;
 pub mod thread;

rust-app/zephyr/src/mempool.rs

@@ -0,0 +1,36 @@
+use core::alloc::{GlobalAlloc, Layout};
+
+pub use zephyr_sys::raw::sys_mem_pool;
+
+pub struct MempoolAlloc(pub &'static sys_mem_pool);
+
+unsafe impl Send for MempoolAlloc {}
+unsafe impl Sync for MempoolAlloc {}
+
+unsafe impl GlobalAlloc for MempoolAlloc {
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        zephyr_sys::raw::sys_mem_pool_alloc(self.0 as *const _ as *mut _, layout.size()) as *mut _
+    }
+
+    unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
+        zephyr_sys::raw::sys_mem_pool_free(ptr as *mut _)
+    }
+}
+
+/// Assign a Zephyr sys mem pool as #[global_allocator]
+///
+/// This should be defined with SYS_MEM_POOL_DEFINE and granted permission to any
+/// Rust threads that need to use libstd or alloc.
+#[macro_export]
+macro_rules! global_sys_mem_pool {
+    ($pool:ident) => {
+        extern "C" {
+            #[no_mangle]
+            static $pool: $crate::mempool::sys_mem_pool;
+        }
+
+        #[global_allocator]
+        static GLOBAL: $crate::mempool::MempoolAlloc =
+            $crate::mempool::MempoolAlloc(unsafe { &$pool });
+    };
+}

syscall_thunk.c

@@ -1,5 +1,6 @@
 #define __ZEPHYR_DEFINE_SYSCALLS__
 #include <rust_syscall_macros.h>
 #include <kernel.h>
+#include <misc/mempool.h>
 #include <device.h>
 #include <uart.h>