aarch64: ensure bti c is emitted at function start [PR94697]

The bti pass currently first emits bti c at function start
if there is no paciasp (which also acts as indirect call
landing pad), then bti j is emitted at jump labels, however
if there is a label right before paciasp then the function
start can end up like

  foo:
  label:
    bti j
    paciasp
    ...

This patch is a minimal fix that just moves the bti c handling
after the bti j handling so we end up with

  foo:
    bti c
  label:
    bti j
    paciasp
    ...

This could be improved by emitting bti jc in this case, or by
detecting that the label is not in fact an indirect jump target
and then this situation would be much less common.

Needs to be backported to gcc-9 branch.

gcc/ChangeLog:

	PR target/94697
	* config/aarch64/aarch64-bti-insert.c (rest_of_insert_bti): Swap
	bti c and bti j handling.

gcc/testsuite/ChangeLog:

	PR target/94697
	* gcc.target/aarch64/pr94697.c: New test.

4 files changed, 46 insertions, 16 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 4e427c0..c806e5e 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2020-04-23  Szabolcs Nagy  <szabolcs.nagy@arm.com>
+
+	PR target/94697
+	* config/aarch64/aarch64-bti-insert.c (rest_of_insert_bti): Swap
+	bti c and bti j handling.
+
 2020-04-23  Andrew Stubbs  <ams@codesourcery.com>
 	    Thomas Schwinge  <thomas@codesourcery.com>
 
diff --git a/gcc/config/aarch64/aarch64-bti-insert.c b/gcc/config/aarch64/aarch64-bti-insert.c
index 295d18a..aa091c3 100644
--- a/gcc/config/aarch64/aarch64-bti-insert.c
+++ b/gcc/config/aarch64/aarch64-bti-insert.c
@@ -132,22 +132,6 @@ rest_of_insert_bti (void)
   rtx_insn *insn;
   basic_block bb;
 
-  /* Since a Branch Target Exception can only be triggered by an indirect call,
-     we exempt function that are only called directly.  We also exempt
-     functions that are already protected by Return Address Signing (PACIASP/
-     PACIBSP).  For all other cases insert a BTI C at the beginning of the
-     function.  */
-  if (!cgraph_node::get (cfun->decl)->only_called_directly_p ())
-    {
-      bb = ENTRY_BLOCK_PTR_FOR_FN (cfun)->next_bb;
-      insn = BB_HEAD (bb);
-      if (!aarch64_pac_insn_p (get_first_nonnote_insn ()))
-	{
-	  bti_insn = gen_bti_c ();
-	  emit_insn_before (bti_insn, insn);
-	}
-    }
-
   bb = 0;
   FOR_EACH_BB_FN (bb, cfun)
     {
@@ -203,6 +187,22 @@ rest_of_insert_bti (void)
 	}
     }
 
+  /* Since a Branch Target Exception can only be triggered by an indirect call,
+     we exempt function that are only called directly.  We also exempt
+     functions that are already protected by Return Address Signing (PACIASP/
+     PACIBSP).  For all other cases insert a BTI C at the beginning of the
+     function.  */
+  if (!cgraph_node::get (cfun->decl)->only_called_directly_p ())
+    {
+      bb = ENTRY_BLOCK_PTR_FOR_FN (cfun)->next_bb;
+      insn = BB_HEAD (bb);
+      if (!aarch64_pac_insn_p (get_first_nonnote_insn ()))
+	{
+	  bti_insn = gen_bti_c ();
+	  emit_insn_before (bti_insn, insn);
+	}
+    }
+
   timevar_pop (TV_MACH_DEP);
   return 0;
 }
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 4f5f020..15e7d9e 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-04-23  Szabolcs Nagy  <szabolcs.nagy@arm.com>
+
+	PR target/94697
+	* gcc.target/aarch64/pr94697.c: New test.
+
 2020-04-23  Felix Yang  <felix.yang@huawei.com>
 
 	PR target/94678
diff --git a/gcc/testsuite/gcc.target/aarch64/pr94697.c b/gcc/testsuite/gcc.target/aarch64/pr94697.c
new file mode 100644
index 0000000..e6069d2
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/pr94697.c
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mbranch-protection=standard" } */
+/* { dg-final { check-function-bodies "**" "" } } */
+
+void bar (int *);
+void *addr;
+
+/*
+** foo:
+**	hint	(25|34|38) // (paciasp|bti c|bti jc)
+**	...
+*/
+int foo (int x)
+{
+label:
+  addr = &&label;
+  bar (&x);
+  return x;
+}