From 0eec8b4e6cd2b309254a93626608aaa425aa6077 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Tue, 26 Oct 2021 15:46:59 -0700
Subject: Add -fcf-check-attribute=[yes|no]

-fcf-check-attribute=[yes|no] implies "cf_check" or "nocf_check" function
attribute.

diff --git a/gcc/attribs.c b/gcc/attribs.c
index 47969bd77426..f3ebb6b5f166 100644
--- a/gcc/attribs.c
+++ b/gcc/attribs.c
@@ -541,6 +541,25 @@ decl_attributes (tree *node, tree attributes, int flags,
 	attributes = tree_cons (get_identifier ("no_icf"),  NULL, attributes);
     }
 
+  /* -fcf-check-attribute=[yes|no] implies "cf_check" or "nocf_check"
+     function attribute.  */
+  if (TREE_CODE (*node) == FUNCTION_DECL
+      && flag_cf_check_attribute != CF_CHECK_ATTRIBUTE_NONE
+      && !fndecl_built_in_p (*node)
+      && lookup_attribute ("nocf_check",
+			   DECL_ATTRIBUTES (*node)) == nullptr
+      && lookup_attribute ("cf_check",
+			   DECL_ATTRIBUTES (*node)) == nullptr
+      && (!attributes
+	  || (lookup_attribute ("nocf_check", attributes) == nullptr
+	      && lookup_attribute ("cf_check", attributes) == nullptr)))
+    {
+      const char *attr = (flag_cf_check_attribute == CF_CHECK_ATTRIBUTE_YES
+			  ? "cf_check" : "nocf_check");
+      attributes = tree_cons (get_identifier (attr), nullptr,
+			      attributes);
+    }
+
   targetm.insert_attributes (*node, &attributes);
 
   /* Note that attributes on the same declaration are not necessarily
diff --git a/gcc/c/c-decl.c b/gcc/c/c-decl.c
index ddef9c68fb7e..ef7d8087e7b9 100644
--- a/gcc/c/c-decl.c
+++ b/gcc/c/c-decl.c
@@ -2130,7 +2130,27 @@ diagnose_mismatched_decls (tree newdecl, tree olddecl,
 		error ("conflicting type qualifiers for %q+D", newdecl);
 	    }
 	  else
-	    error ("conflicting types for %q+D; have %qT", newdecl, newtype);
+	    {
+	      if (flag_cf_check_attribute == CF_CHECK_ATTRIBUTE_NO
+		  && (!lookup_attribute ("nocf_check",
+					  TYPE_ATTRIBUTES (oldtype))
+		       != !lookup_attribute ("nocf_check",
+					     TYPE_ATTRIBUTES (newtype))))
+		error ("conflicting types for %q+D; have %qT with "
+		       "implied %<nocf_check%> attribute",
+		       newdecl, newtype);
+	      else if (flag_cf_check_attribute == CF_CHECK_ATTRIBUTE_YES
+		       && (!lookup_attribute ("cf_check",
+					     TYPE_ATTRIBUTES (oldtype))
+			  != !lookup_attribute ("cf_check",
+						TYPE_ATTRIBUTES (newtype))))
+		error ("conflicting types for %q+D; have %qT with "
+		       "implied %<cf_check%> attribute",
+		       newdecl, newtype);
+	      else
+		error ("conflicting types for %q+D; have %qT",
+		       newdecl, newtype);
+	    }
 	  diagnose_arglist_conflict (newdecl, olddecl, newtype, oldtype);
 	  locate_old_decl (olddecl);
 	  return false;
diff --git a/gcc/common.opt b/gcc/common.opt
index a75b44ee47e7..e77c539354aa 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -1805,6 +1805,22 @@ Enum(cf_protection_level) String(check) Value(CF_CHECK)
 EnumValue
 Enum(cf_protection_level) String(none) Value(CF_NONE)
 
+fcf-check-attribute=
+Target RejectNegative Joined Enum(cf_check_attribute) Var(flag_cf_check_attribute) Init(CF_CHECK_ATTRIBUTE_NONE)
+-fcf-check-attribute=[none|yes|no] Select the default cf_check attribute.
+
+Enum
+Name(cf_check_attribute) Type(enum cf_check_attribute) UnknownError(unknown default Control-Flow attribute %qs)
+
+EnumValue
+Enum(cf_check_attribute) String(none) Value(CF_CHECK_ATTRIBUTE_NONE)
+
+EnumValue
+Enum(cf_check_attribute) String(yes) Value(CF_CHECK_ATTRIBUTE_YES)
+
+EnumValue
+Enum(cf_check_attribute) String(no) Value(CF_CHECK_ATTRIBUTE_NO)
+
 finstrument-functions
 Common Var(flag_instrument_function_entry_exit)
 Instrument function entry and exit with profiling calls.
diff --git a/gcc/flag-types.h b/gcc/flag-types.h
index a038c8fb738f..dabd7832754d 100644
--- a/gcc/flag-types.h
+++ b/gcc/flag-types.h
@@ -397,6 +397,14 @@ enum cf_protection_level
   CF_CHECK = 1 << 3
 };
 
+/* Default Control-Flow Protection attribute.  */
+enum cf_check_attribute
+{
+  CF_CHECK_ATTRIBUTE_NONE = 0,
+  CF_CHECK_ATTRIBUTE_YES,
+  CF_CHECK_ATTRIBUTE_NO
+};
+
 /* Parloops schedule type.  */
 enum parloops_schedule_type
 {
diff --git a/gcc/testsuite/gcc.target/i386/pr102953-1.c b/gcc/testsuite/gcc.target/i386/pr102953-1.c
new file mode 100644
index 000000000000..fd92c9c577ea
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr102953-1.c
@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-options "-Wall -fcf-protection -mmanual-endbr -fcf-check-attribute=no" } */
+
+static void __attribute__((cf_check)) foo(void);
+static void foo(void) /* { dg-error "implied 'nocf_check' attribute" } */
+{
+}
+void (*ptr)(void) = foo; /* { dg-warning "incompatible pointer type" } */
diff --git a/gcc/testsuite/gcc.target/i386/pr102953-2.c b/gcc/testsuite/gcc.target/i386/pr102953-2.c
new file mode 100644
index 000000000000..cd8f42791807
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr102953-2.c
@@ -0,0 +1,7 @@
+/* { dg-do compile } */
+/* { dg-options "-Wall -fcf-protection -mmanual-endbr -fcf-check-attribute=no" } */
+
+static void foo(void)
+{
+}
+void (*ptr)(void) = foo; /* { dg-warning "incompatible pointer type" } */
diff --git a/gcc/testsuite/gcc.target/i386/pr102953-3.c b/gcc/testsuite/gcc.target/i386/pr102953-3.c
new file mode 100644
index 000000000000..b1bd4afe85fd
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr102953-3.c
@@ -0,0 +1,7 @@
+/* { dg-do compile } */
+/* { dg-options "-Wall -fcf-protection -mmanual-endbr -fcf-check-attribute=no" } */
+
+extern void foo(void);
+void __attribute__((cf_check)) foo(void) /* { dg-error "implied 'nocf_check' attribute" } */
+{
+}
diff --git a/gcc/testsuite/gcc.target/i386/pr102953-4.c b/gcc/testsuite/gcc.target/i386/pr102953-4.c
new file mode 100644
index 000000000000..ee0c66f94cb5
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr102953-4.c
@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-options "-Wall -fcf-protection -mmanual-endbr -fcf-check-attribute=no" } */
+
+static int __attribute__((cf_check)) foo(char a[], int b)
+{
+  return 0;
+}
+int (*ptr)(char[], int) = foo;