[3/8,V8M,arm-embedded] Handling ARMv8-M Security Extension's cmse_nonsecure_entry attribute

diff --git a/gcc/config/arm/arm.h b/gcc/config/arm/arm.h
index 7574064936e5217c8e553e7ab744cbe9320346d2..3467a9ea3d3c59b0b41a59f22f14f277153cff0e 100644
--- a/gcc/config/arm/arm.h
+++ b/gcc/config/arm/arm.h
@@ -1510,6 +1510,7 @@  do {									      \
 #define ARM_FT_VOLATILE		(1 << 4) /* Does not return.  */
 #define ARM_FT_NESTED		(1 << 5) /* Embedded inside another func.  */
 #define ARM_FT_STACKALIGN	(1 << 6) /* Called with misaligned stack.  */
+#define ARM_FT_CMSE_ENTRY	(1 << 7) /* ARMv8-M non-secure entry function.  */
 
 /* Some macros to test these flags.  */
 #define ARM_FUNC_TYPE(t)	(t & ARM_FT_TYPE_MASK)
@@ -1518,6 +1519,7 @@  do {									      \
 #define IS_NAKED(t)        	(t & ARM_FT_NAKED)
 #define IS_NESTED(t)       	(t & ARM_FT_NESTED)
 #define IS_STACKALIGN(t)       	(t & ARM_FT_STACKALIGN)
+#define IS_CMSE_ENTRY(t)	(t & ARM_FT_CMSE_ENTRY)
 
 
 /* Structure used to hold the function stack frame layout.  Offsets are
diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index 8c951490f0fa4eb5a5d14a1aaaaca75a51bdbe03..d53d96e7e52cdcc3c2340d714d277e12a1ee07f6 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -167,6 +167,7 @@  static tree arm_handle_isr_attribute (tree *, tree, tree, int, bool *);
 #if TARGET_DLLIMPORT_DECL_ATTRIBUTES
 static tree arm_handle_notshared_attribute (tree *, tree, tree, int, bool *);
 #endif
+static tree arm_handle_cmse_nonsecure_entry (tree *, tree, tree, int, bool *);
 static void arm_output_function_epilogue (FILE *, HOST_WIDE_INT);
 static void arm_output_function_prologue (FILE *, HOST_WIDE_INT);
 static int arm_comp_type_attributes (const_tree, const_tree);
@@ -368,6 +369,9 @@  static const struct attribute_spec arm_attribute_table[] =
   { "notshared",    0, 0, false, true, false, arm_handle_notshared_attribute,
     false },
 #endif
+  /* ARMv8-M Security Extensions support.  */
+  { "cmse_nonsecure_entry", 0, 0, true, false, false,
+    arm_handle_cmse_nonsecure_entry, false },
   { NULL,           0, 0, false, false, false, NULL, false }
 };
 
@@ -3354,6 +3358,9 @@  arm_compute_func_type (void)
   else
     type |= arm_isr_value (TREE_VALUE (a));
 
+  if (lookup_attribute ("cmse_nonsecure_entry", attr))
+    type |= ARM_FT_CMSE_ENTRY;
+
   return type;
 }
 
@@ -6348,6 +6355,109 @@  arm_handle_notshared_attribute (tree *node,
 }
 #endif
 
+/* This function is used to check whether functions with attributes
+   cmse_nonsecure_call or cmse_nonsecure_entry use the stack to pass arguments
+   or return variables.  If the function does indeed use the stack this
+   function returns true and diagnoses this, otherwise it returns false.  */
+
+static bool
+cmse_func_args_or_return_in_stack (tree fndecl, tree name, tree fntype)
+{
+  function_args_iterator args_iter;
+  CUMULATIVE_ARGS args_so_far_v;
+  cumulative_args_t args_so_far;
+  bool first_param = true;
+  tree arg_type, prev_arg_type = NULL_TREE, ret_type;
+
+  /* Error out if any argument is passed on the stack.  */
+  arm_init_cumulative_args (&args_so_far_v, fntype, NULL_RTX, fndecl);
+  args_so_far = pack_cumulative_args (&args_so_far_v);
+  FOREACH_FUNCTION_ARGS (fntype, arg_type, args_iter)
+    {
+      rtx arg_rtx;
+      machine_mode arg_mode = TYPE_MODE (arg_type);
+
+      prev_arg_type = arg_type;
+      if (VOID_TYPE_P (arg_type))
+	continue;
+
+      if (!first_param)
+	arm_function_arg_advance (args_so_far, arg_mode, arg_type, true);
+      arg_rtx = arm_function_arg (args_so_far, arg_mode, arg_type, true);
+      if (!arg_rtx
+	  || arm_arg_partial_bytes (args_so_far, arg_mode, arg_type, true))
+	{
+	  error ("%qE attribute not available to functions with arguments "
+		 "passed on the stack", name);
+	  return true;
+	}
+      first_param = false;
+    }
+
+  /* Error out for variadic functions since we cannot control how many
+     arguments will be passed and thus stack could be used.  stdarg_p () is not
+     used for the checking to avoid browsing arguments twice.  */
+  if (prev_arg_type != NULL_TREE && !VOID_TYPE_P (prev_arg_type))
+    {
+      error ("%qE attribute not available to functions with variable number "
+	     "of arguments", name);
+      return true;
+    }
+
+  /* Error out if return value is passed on the stack.  */
+  ret_type = TREE_TYPE (fntype);
+  if (arm_return_in_memory (ret_type, fntype))
+    {
+      error ("%qE attribute not available to functions that return value on "
+	     "the stack", name);
+      return true;
+    }
+  return false;
+}
+
+/* Called upon detection of the use of the cmse_nonsecure_entry attribute, this
+   function will check whether the attribute is allowed here and will add the
+   attribute to the function declaration tree or otherwise issue a warning.  */
+
+static tree
+arm_handle_cmse_nonsecure_entry (tree *node, tree name,
+				 tree /* args */,
+				 int /* flags */,
+				 bool *no_add_attrs)
+{
+  tree fndecl;
+
+  if (!use_cmse)
+    {
+      *no_add_attrs = true;
+      return NULL_TREE;
+    }
+
+  /* Ignore attribute for function types.  */
+  if (TREE_CODE (*node) != FUNCTION_DECL)
+    {
+      warning (OPT_Wattributes, "%qE attribute only applies to functions",
+	       name);
+      *no_add_attrs = true;
+      return NULL_TREE;
+    }
+
+  fndecl = *node;
+
+  /* Warn for static linkage functions.  */
+  if (!TREE_PUBLIC (fndecl))
+    {
+      warning (OPT_Wattributes, "%qE attribute has no effect on functions "
+	       "with static linkage", name);
+      *no_add_attrs = true;
+      return NULL_TREE;
+    }
+
+  *no_add_attrs |= cmse_func_args_or_return_in_stack (fndecl, name,
+						TREE_TYPE (fndecl));
+  return NULL_TREE;
+}
+
 /* Return 0 if the attributes for two types are incompatible, 1 if they
    are compatible, and 2 if they are nearly compatible (which causes a
    warning to be generated).  */
diff --git a/gcc/testsuite/gcc.target/arm/cmse/cmse-3.c b/gcc/testsuite/gcc.target/arm/cmse/cmse-3.c
new file mode 100644
index 0000000000000000000000000000000000000000..f806951e90256e8286d2d0f9467b51a73a522e2b
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/cmse/cmse-3.c
@@ -0,0 +1,38 @@ 
+/* { dg-do compile } */
+/* { dg-require-effective-target arm_cmse_ok } */
+/* { dg-options "-mcmse" }  */
+
+struct span {
+  int a, b;
+};
+struct span2 {
+  float a, b, c, d;
+};
+
+union test_union
+{
+  long long a;
+  int b;
+  struct span2 c;
+} test_union;
+
+void __attribute__ ((cmse_nonsecure_entry))
+foo (long long a, int b, long long c) {} /* { dg-error "not available to functions with arguments passed on the stack" } */
+
+void __attribute__ ((cmse_nonsecure_entry))
+bar (long long a, int b, struct span c) {} /* { dg-error "not available to functions with arguments passed on the stack" } */
+
+void __attribute__ ((cmse_nonsecure_entry))
+baz (int a, ...) {} /* { dg-error "not available to functions with variable number of arguments" } */
+
+struct span __attribute__ ((cmse_nonsecure_entry))
+qux (void) { /* { dg-error "not available to functions that return value on the stack" } */
+  struct span ret = {0, 0};
+  return ret;
+}
+
+void __attribute__ ((cmse_nonsecure_entry))
+norf (struct span2 a) {}
+
+void __attribute__ ((cmse_nonsecure_entry))
+foo2 (long long a, int b, union test_union c) {} /* { dg-error "not available to functions with arguments passed on the stack" } */