[PATCH] i386; Add -mmanual-endbr and cf_check function attribute

["H.J. Lu" <hongjiu dot lu at intel dot com>]

Currently GCC inserts ENDBR instruction at entries of all non-static
functions, unless LTO compilation is used.  Marking all functions,
which are not called indirectly with nocf_check attribute, is not
ideal since 99% of functions in a program may be of this kind.

This patch adds -mmanual-endbr and cf_check function attribute.  They
can be used together with -fcf-protection such that ENDBR instruction
is inserted only at entries of functions with cf_check attribute.  It
can limit number of ENDBR instructions to reduce program size.

OK for trubk?

H.J.
-----
gcc/

	* config/i386/i386.c (rest_of_insert_endbranch): Insert ENDBR
	at the function entry only when -mmanual-endbr isn't used or
	there is cf_check function attribute.
	(ix86_attribute_table): Add cf_check.
	* config/i386/i386.opt: Add -mmanual-endbr.
	* doc/extend.texi: Document cf_check attribute.
	* doc/invoke.texi: Document -mmanual-endbr.

gcc/testsuite/

	* gcc.target/i386/cf_check-1.c: New test.
	* gcc.target/i386/cf_check-2.c: Likewise.
	* gcc.target/i386/cf_check-3.c: Likewise.
	* gcc.target/i386/cf_check-4.c: Likewise.
	* gcc.target/i386/cf_check-5.c: Likewise.
---
 gcc/config/i386/i386.c                     |  5 +++++
 gcc/config/i386/i386.opt                   |  5 +++++
 gcc/doc/extend.texi                        |  7 +++++++
 gcc/doc/invoke.texi                        |  9 ++++++++-
 gcc/testsuite/gcc.target/i386/cf_check-1.c | 11 +++++++++++
 gcc/testsuite/gcc.target/i386/cf_check-2.c | 11 +++++++++++
 gcc/testsuite/gcc.target/i386/cf_check-3.c | 11 +++++++++++
 gcc/testsuite/gcc.target/i386/cf_check-4.c | 10 ++++++++++
 gcc/testsuite/gcc.target/i386/cf_check-5.c |  9 +++++++++
 9 files changed, 77 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.target/i386/cf_check-1.c
 create mode 100644 gcc/testsuite/gcc.target/i386/cf_check-2.c
 create mode 100644 gcc/testsuite/gcc.target/i386/cf_check-3.c
 create mode 100644 gcc/testsuite/gcc.target/i386/cf_check-4.c
 create mode 100644 gcc/testsuite/gcc.target/i386/cf_check-5.c

diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 95cfa05ce61..d356e0e7acd 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -2604,6 +2604,9 @@ rest_of_insert_endbranch (void)
 
   if (!lookup_attribute ("nocf_check",
 			 TYPE_ATTRIBUTES (TREE_TYPE (cfun->decl)))
+      && (!flag_manual_endbr
+	  || lookup_attribute ("cf_check",
+			       DECL_ATTRIBUTES (cfun->decl)))
       && !cgraph_node::get (cfun->decl)->only_called_directly_p ())
     {
       cet_eb = gen_nop_endbr ();
@@ -45896,6 +45899,8 @@ static const struct attribute_spec ix86_attribute_table[] =
     ix86_handle_fndecl_attribute, NULL },
   { "function_return", 1, 1, true, false, false, false,
     ix86_handle_fndecl_attribute, NULL },
+  { "cf_check", 0, 0, true, false, false, false,
+    ix86_handle_fndecl_attribute, NULL },
 
   /* End element.  */
   { NULL, 0, 0, false, false, false, false, NULL, NULL }
diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
index a34d4acf1a2..aebc023420b 100644
--- a/gcc/config/i386/i386.opt
+++ b/gcc/config/i386/i386.opt
@@ -1016,6 +1016,11 @@ Target Report Undocumented Var(flag_cet_switch) Init(0)
 Turn on CET instrumentation for switch statements that use a jump table and
 an indirect jump.
 
+mmanual-endbr
+Target Report Var(flag_manual_endbr) Init(0)
+Insert ENDBR instruction at function entry only via cf_check attribute
+for CET instrumentation.
+
 mforce-indirect-call
 Target Report Var(flag_force_indirect_call) Init(0)
 Make all function calls indirect.
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index e0a84b8b3c5..5fd4a1b22b0 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -5864,6 +5864,13 @@ foo (void)
 @}
 @end smallexample
 
+@item cf_check
+@cindex @code{cf_check} function attribute, x86
+
+The @code{cf_check} attribute on a function is used to inform the
+compiler that ENDBR instruction should be placed at the function
+entry when @option{-fcf-protection=branch} is enabled.
+
 @end table
 
 On the x86, the inliner does not inline a
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 940b84697fa..7ec4267b7b1 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -1250,7 +1250,7 @@ See RS/6000 and PowerPC Options.
 -msse4a  -m3dnow  -m3dnowa  -mpopcnt  -mabm  -mbmi  -mtbm  -mfma4  -mxop @gol
 -mlzcnt  -mbmi2  -mfxsr  -mxsave  -mxsaveopt  -mrtm  -mlwp @gol
 -mmwaitx  -mclzero  -mpku  -mthreads -mgfni  -mvaes  -mwaitpkg @gol
--mshstk -mforce-indirect-call -mavx512vbmi2 @gol
+-mshstk -mforce-indirect-call -mmanual-endbr -mavx512vbmi2 @gol
 -mvpclmulqdq -mavx512bitalg -mmovdiri -mmovdir64b -mavx512vpopcntdq
 -mcldemote @gol
 -mms-bitfields  -mno-align-stringops  -minline-all-stringops @gol
@@ -27476,6 +27476,13 @@ Force all calls to functions to be indirect. This is useful
 when using Intel Processor Trace where it generates more precise timing
 information for function calls.
 
+@item -mmanual-endbr
+@opindex mmanual-endbr
+Insert ENDBR instruction at function entry only via the @code{cf_check}
+function attribute. This is useful when used with the option
+@option{-fcf-protection=branch} to control ENDBR insertion at the
+function entry.
+
 @item -mcall-ms2sysv-xlogues
 @opindex mcall-ms2sysv-xlogues
 @opindex mno-call-ms2sysv-xlogues
diff --git a/gcc/testsuite/gcc.target/i386/cf_check-1.c b/gcc/testsuite/gcc.target/i386/cf_check-1.c
new file mode 100644
index 00000000000..c433eab854a
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/cf_check-1.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fcf-protection -mmanual-endbr" } */
+/* { dg-final { scan-assembler-not {\mendbr} } } */
+
+extern void bar (void) __attribute__((__cf_check__));
+
+void
+foo (void)
+{
+  bar ();
+}
diff --git a/gcc/testsuite/gcc.target/i386/cf_check-2.c b/gcc/testsuite/gcc.target/i386/cf_check-2.c
new file mode 100644
index 00000000000..e2b9c4dbcb2
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/cf_check-2.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fcf-protection -mno-manual-endbr" } */
+/* { dg-final { scan-assembler-times {\mendbr} 1 } } */
+
+extern void bar (void) __attribute__((__cf_check__));
+
+void
+foo (void)
+{
+  bar ();
+}
diff --git a/gcc/testsuite/gcc.target/i386/cf_check-3.c b/gcc/testsuite/gcc.target/i386/cf_check-3.c
new file mode 100644
index 00000000000..d835cc3a21b
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/cf_check-3.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fcf-protection=none" } */
+/* { dg-final { scan-assembler-not {\mendbr} } } */
+
+extern void bar (void) __attribute__((__cf_check__));
+
+void
+foo (void)
+{
+  bar ();
+}
diff --git a/gcc/testsuite/gcc.target/i386/cf_check-4.c b/gcc/testsuite/gcc.target/i386/cf_check-4.c
new file mode 100644
index 00000000000..d6cb27cf20b
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/cf_check-4.c
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fcf-protection -mmanual-endbr" } */
+/* { dg-final { scan-assembler-times {\mendbr} 1 } } */
+
+extern void foo (void) __attribute__((__cf_check__));
+
+void
+foo (void)
+{
+}
diff --git a/gcc/testsuite/gcc.target/i386/cf_check-5.c b/gcc/testsuite/gcc.target/i386/cf_check-5.c
new file mode 100644
index 00000000000..f2c0c5c2c09
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/cf_check-5.c
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fcf-protection -mmanual-endbr" } */
+/* { dg-final { scan-assembler-times {\mendbr} 1 } } */
+
+__attribute__((__cf_check__))
+void
+foo (void)
+{
+}
-- 
2.17.1