switcher: move some constants to misc-assembly.h

These are not really "trusted stack", and we're about to have some more.
While here, tweak a comment as per Robert's suggestion.

Co-authored-by: Robert Norton <robert.norton@microsoft.com>

sdk/core/loader/boot.cc

diff --git a/sdk/core/loader/boot.cc b/sdk/core/loader/boot.cc
index 5bcb70c..332a491 100644
--- a/sdk/core/loader/boot.cc
+++ b/sdk/core/loader/boot.cc
@@ -11,6 +11,7 @@
 #include <string.h>
 
 #include "../switcher/tstack.h"
+#include "../switcher/misc-assembly.h"
 #include "constants.h"
 #include "debug.hh"
 #include "defines.h"

sdk/core/switcher/entry.S

diff --git a/sdk/core/switcher/entry.S b/sdk/core/switcher/entry.S
index 3a3eeb1..eb85ef7 100644
--- a/sdk/core/switcher/entry.S
+++ b/sdk/core/switcher/entry.S
@@ -3,6 +3,7 @@
 
 #include "export-table-assembly.h"
 #include "trusted-stack-assembly.h"
+#include "misc-assembly.h"
 #include <errno.h>
 
 .include "assembly-helpers.s"

sdk/core/switcher/misc-assembly.h

diff --git a/sdk/core/switcher/misc-assembly.h b/sdk/core/switcher/misc-assembly.h
new file mode 100644
index 0000000..f48e59f
--- /dev/null
+++ b/sdk/core/switcher/misc-assembly.h
@@ -0,0 +1,28 @@
+// Copyright CHERIoT Contributors.
+// SPDX-License-Identifier: MIT
+
+#pragma once
+#include <assembly-helpers.h>
+
+/*
+ * Constant to represent the raw permissions of the compartment CSP.  We use
+ * this in the switcher, to verify the permissions of the CSP that comes from
+ * the compartment are exactly what we expect.
+ */
+EXPORT_ASSEMBLY_EXPRESSION(COMPARTMENT_STACK_PERMISSIONS,
+                           (CHERI::PermissionSet{
+                             CHERI::Permission::Load,
+                             CHERI::Permission::Store,
+                             CHERI::Permission::LoadStoreCapability,
+                             CHERI::Permission::LoadMutable,
+                             CHERI::Permission::StoreLocal,
+                             CHERI::Permission::LoadGlobal}
+                              .as_raw()),
+                           0x7e)
+
+/**
+ * Space reserved at the top of a stack on entry to the compartment.
+ *
+ * This *must* be a multiple of 16, which is the stack alignment.
+ */
+#define STACK_ENTRY_RESERVED_SPACE 16

sdk/core/switcher/trusted-stack-assembly.h

diff --git a/sdk/core/switcher/trusted-stack-assembly.h b/sdk/core/switcher/trusted-stack-assembly.h
index 660a010..7969662 100644
--- a/sdk/core/switcher/trusted-stack-assembly.h
+++ b/sdk/core/switcher/trusted-stack-assembly.h
@@ -57,18 +57,3 @@
 
 #define TSTACKOFFSET_FIRSTFRAME                                                \
 	(TrustedStack_offset_frameoffset + TSTACK_HEADER_SZ)
-
-/* Constant to represent the raw permissions of the compartment CSP.
- *  We use this in the switcher, to verify the CSP comes from the
- *  compartment is exactly what we expect.
- *  This represents the following permissions:
- *  Load, Store, LoadStoreCapability, LoadMutable StoreLocal and LoadGlobal
- */
-#define COMPARTMENT_STACK_PERMISSIONS 0x7e
-
-/**
- * Space reserved at the top of a stack on entry to the compartment.
- *
- * This *must* be a multiple of 16, which is the stack alignment.
- */
-#define STACK_ENTRY_RESERVED_SPACE 16

sdk/core/switcher/tstack.h

diff --git a/sdk/core/switcher/tstack.h b/sdk/core/switcher/tstack.h
index d782af8..dc8338b 100644
--- a/sdk/core/switcher/tstack.h
+++ b/sdk/core/switcher/tstack.h
@@ -77,13 +77,3 @@
 using TrustedStack = TrustedStackGeneric<0>;
 
 #include "trusted-stack-assembly.h"
-
-static_assert(
-  CheckSize<COMPARTMENT_STACK_PERMISSIONS,
-            CHERI::PermissionSet{CHERI::Permission::Load,
-                                 CHERI::Permission::Store,
-                                 CHERI::Permission::LoadStoreCapability,
-                                 CHERI::Permission::LoadMutable,
-                                 CHERI::Permission::StoreLocal,
-                                 CHERI::Permission::LoadGlobal}
-              .as_raw()>::value);