Add -fcf-check-attribute=[yes|no|none] for Linux kernel

diff --git a/gcc/attribs.cc b/gcc/attribs.cc
index 497dcff84df..4af9df5d976 100644
--- a/gcc/attribs.cc
+++ b/gcc/attribs.cc
@@ -689,6 +689,25 @@  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.cc b/gcc/c/c-decl.cc
index c701f07befe..787c39dc0fe 100644
--- a/gcc/c/c-decl.cc
+++ b/gcc/c/c-decl.cc
@@ -2133,7 +2133,27 @@  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 c21e5273ae3..b6353e5587f 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -1873,6 +1873,22 @@  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 implied function 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/doc/invoke.texi b/gcc/doc/invoke.texi
index fb3dec4ab0c..a24f435b370 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -605,6 +605,7 @@  Objective-C and Objective-C++ Dialects}.
 -fasan-shadow-offset=@var{number}  -fsanitize-sections=@var{s1},@var{s2},... @gol
 -fsanitize-undefined-trap-on-error  -fbounds-check @gol
 -fcf-protection=@r{[}full@r{|}branch@r{|}return@r{|}none@r{|}check@r{]} @gol
+-fcf-check-attribute=@r{[}none@r{|}yes@r{|}no@r{]} @gol
 -fharden-compares -fharden-conditional-branches @gol
 -fstack-protector  -fstack-protector-all  -fstack-protector-strong @gol
 -fstack-protector-explicit  -fstack-check @gol
@@ -15971,6 +15972,17 @@  Currently the x86 GNU/Linux target provides an implementation based
 on Intel Control-flow Enforcement Technology (CET) which works for
 i686 processor or newer.
 
+@item -fcf-check-attribute=@r{[}none@r{|}yes@r{|}no@r{]}
+@opindex fcf-check-attribute
+Select the implied function attribute for code instrumentation of
+control-flow transfers.
+
+The value @code{yes} makes the @code{cf_check} attribute implied on
+functions.  The value @code{no} makes the @code{nocf_check} attribute
+implied on functions.  The value @code{none}, which is the default,
+doesn't imply the @code{cf_check} nor @code{nocf_check} attributes on
+functions.
+
 @item -fharden-compares
 @opindex fharden-compares
 For every logical test that survives gimple optimizations and is
diff --git a/gcc/flag-types.h b/gcc/flag-types.h
index 2c8498169e0..c84d67b1ac8 100644
--- a/gcc/flag-types.h
+++ b/gcc/flag-types.h
@@ -449,6 +449,14 @@  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/pr102953-3.c b/gcc/testsuite/gcc.target/i386/pr102953-3.c
new file mode 100644
index 00000000000..fd92c9c577e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr102953-3.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/pr102953-4.c b/gcc/testsuite/gcc.target/i386/pr102953-4.c
new file mode 100644
index 00000000000..cd8f4279180
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr102953-4.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/pr102953-5.c b/gcc/testsuite/gcc.target/i386/pr102953-5.c
new file mode 100644
index 00000000000..b1bd4afe85f
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr102953-5.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/pr102953-6.c b/gcc/testsuite/gcc.target/i386/pr102953-6.c
new file mode 100644
index 00000000000..ee0c66f94cb
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr102953-6.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;