[PATCH] i386: Insert ENDBR to trampoline for -fcf-protection=branch -mibt

[H.J. Lu]

When -fcf-protection=branch -mibt are used, we need to insert ENDBR
to trampoline.  TRAMPOLINE_SIZE is creased by 4 bytes to accommodate
4-byte ENDBR instruction.

OK for trunk?

H.J.
----
gcc/

        PR target/85044
        * config/i386/i386.c (ix86_trampoline_init): Insert ENDBR for
        -fcf-protection=branch -mibt.
        * config/i386/i386.h (TRAMPOLINE_SIZE): Increased by 4 bytes.

gcc/testsuite/

        PR target/85044
        * gcc.target/i386/pr85044.c: New test.
---
 gcc/config/i386/i386.c                  | 17 +++++++++++++++++
 gcc/config/i386/i386.h                  |  2 +-
 gcc/testsuite/gcc.target/i386/pr85044.c | 24 ++++++++++++++++++++++++
 3 files changed, 42 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.target/i386/pr85044.c

diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 3b264318f50..b4f6aec1434 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -30411,6 +30411,7 @@ ix86_trampoline_init (rtx m_tramp, tree fndecl, rtx 
chain_value)
   rtx mem, fnaddr;
   int opcode;
   int offset = 0;
+  bool need_endbr = (flag_cf_protection & CF_BRANCH) && TARGET_IBT;
 
   fnaddr = XEXP (DECL_RTL (fndecl), 0);
 
@@ -30418,6 +30419,14 @@ ix86_trampoline_init (rtx m_tramp, tree fndecl, rtx 
chain_value)
     {
       int size;
 
+      if (need_endbr)
+       {
+         /* Insert ENDBR64.  */
+         mem = adjust_address (m_tramp, SImode, offset);
+         emit_move_insn (mem, gen_int_mode (0xfa1e0ff3, SImode));
+         offset += 4;
+       }
+
       /* Load the function address to r11.  Try to load address using
         the shorter movl instead of movabs.  We may want to support
         movq for kernel mode, but kernel does not use trampolines at
@@ -30495,6 +30504,14 @@ ix86_trampoline_init (rtx m_tramp, tree fndecl, rtx 
chain_value)
       else
        opcode = 0x68;
 
+      if (need_endbr)
+       {
+         /* Insert ENDBR32.  */
+         mem = adjust_address (m_tramp, SImode, offset);
+         emit_move_insn (mem, gen_int_mode (0xfb1e0ff3, SImode));
+         offset += 4;
+       }
+
       mem = adjust_address (m_tramp, QImode, offset);
       emit_move_insn (mem, gen_int_mode (opcode, QImode));
 
diff --git a/gcc/config/i386/i386.h b/gcc/config/i386/i386.h
index 7f4b04f421d..c7f9b4551b3 100644
--- a/gcc/config/i386/i386.h
+++ b/gcc/config/i386/i386.h
@@ -1716,7 +1716,7 @@ typedef struct ix86_args {
 
 /* Length in units of the trampoline for entering a nested function.  */
 
-#define TRAMPOLINE_SIZE (TARGET_64BIT ? 24 : 10)
+#define TRAMPOLINE_SIZE (TARGET_64BIT ? 28 : 14)
 
 /* Definitions for register eliminations.
 
diff --git a/gcc/testsuite/gcc.target/i386/pr85044.c 
b/gcc/testsuite/gcc.target/i386/pr85044.c
new file mode 100644
index 00000000000..332f582d79b
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr85044.c
@@ -0,0 +1,24 @@
+/* { dg-do run { target cet } } */
+/* { dg-options "-O2 -fcf-protection=branch -mibt" } */
+
+void callme (void (*callback) (void));
+
+int
+main (void)
+{
+  int ok = 0;
+  void callback (void) { ok = 1; }
+
+  callme (&callback);
+
+  if (!ok)
+   __builtin_abort ();
+  return 0;
+}
+
+__attribute__((noinline, noclone))
+void
+callme (void (*callback) (void))
+{
+  (*callback) ();
+}
-- 
2.14.3