kernel/process_standard: Handle null minimum RAM memory

On some architectures, the minimum ammount of memory required to run a
process may be null. This caused a panic in the kernel during
ProcessStandard::create(). The case is now handled by asking the memory
manager for 1 byte if the architecture specifies a null ammount of
memory.

Signed-off-by: Ioan-Cristian CÎRSTEA <ioan.cirstea@oxidos.io>

Author: IoanCristianCirstea

kernel/src/process_standard.rs

@@ -1622,10 +1622,20 @@ impl<C: 'static + Chip, D: 'static + ProcessStandardDebug> ProcessStandard<'_, C
         // the context switching implementation and allocate at least that much
         // memory so that we can successfully switch to the process. This is
         // architecture and implementation specific, so we query that now.
-        let min_process_memory_size = chip
+        let initial_process_app_brk_size = chip
             .userspace_kernel_boundary()
             .initial_process_app_brk_size();
 
+        // Protected allocated region cannot be empty. As such, if the
+        // architecture does not require any memory for a process to start
+        // running, tell the memory manager that the architectures requires 1
+        // byte.
+        let min_process_memory_size = if initial_process_app_brk_size == 0 {
+            1
+        } else {
+            initial_process_app_brk_size
+        };
+
         // We have to ensure that we at least ask the MPU for
         // `min_process_memory_size` so that we can be sure that `app_brk` is
         // not set inside the kernel-owned memory region. Now, in practice,