'Retpoline' mitigation technique for Spectre (branch target injection)
[CVE-2017-5715]:

https://security.googleblog.com/2018/01/more-details-about-mitigations-for-cpu_4.html
https://support.google.com/faqs/answer/7625886
https://spectreattack.com/
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-5715

Patch copied from the 'retpoline-20180107' branch of upstream source repository
(please add new / update existing patches when new 'retpoline-xxxxxxxx' branch
appears):

http://git.infradead.org/users/dwmw2/gcc-retpoline.git

From 0b1769bdce27304a6a91bec234f47f102a2603d5 Mon Sep 17 00:00:00 2001
From: hjl <hjl@138bc75d-0d04-0410-961f-82ee72b054a4>
Date: Mon, 6 Nov 2017 23:04:15 +0000
Subject: [PATCH 02/17] i386: Use reference of struct ix86_frame to avoid copy

When there is no need to make a copy of ix86_frame, we can use reference
of struct ix86_frame to avoid copy.

Tested on x86-64.

	* config/i386/i386.c (ix86_can_use_return_insn_p): Use reference
	of struct ix86_frame.
	(ix86_initial_elimination_offset): Likewise.
	(ix86_expand_split_stack_prologue): Likewise.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@254480 138bc75d-0d04-0410-961f-82ee72b054a4
---
 gcc/config/i386/i386.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index c23c259c538..01ecda7643b 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -11832,8 +11832,6 @@ symbolic_reference_mentioned_p (rtx op)
 bool
 ix86_can_use_return_insn_p (void)
 {
-  struct ix86_frame frame;
-
   /* Don't use `ret' instruction in interrupt handler.  */
   if (! reload_completed
       || frame_pointer_needed
@@ -11846,7 +11844,7 @@ ix86_can_use_return_insn_p (void)
     return 0;
 
   ix86_compute_frame_layout ();
-  frame = cfun->machine->frame;
+  struct ix86_frame &frame = cfun->machine->frame;
   return (frame.stack_pointer_offset == UNITS_PER_WORD
 	  && (frame.nregs + frame.nsseregs) == 0);
 }
@@ -12333,7 +12331,7 @@ HOST_WIDE_INT
 ix86_initial_elimination_offset (int from, int to)
 {
   ix86_compute_frame_layout ();
-  struct ix86_frame frame = cfun->machine->frame;
+  struct ix86_frame &frame = cfun->machine->frame;
 
   if (from == ARG_POINTER_REGNUM && to == HARD_FRAME_POINTER_REGNUM)
     return frame.hard_frame_pointer_offset;
@@ -14849,7 +14847,6 @@ static GTY(()) rtx split_stack_fn_large;
 void
 ix86_expand_split_stack_prologue (void)
 {
-  struct ix86_frame frame;
   HOST_WIDE_INT allocate;
   unsigned HOST_WIDE_INT args_size;
   rtx_code_label *label;
@@ -14862,7 +14859,7 @@ ix86_expand_split_stack_prologue (void)
 
   ix86_finalize_stack_realign_flags ();
   ix86_compute_frame_layout ();
-  frame = cfun->machine->frame;
+  struct ix86_frame &frame = cfun->machine->frame;
   allocate = frame.stack_pointer_offset - INCOMING_FRAME_SP_OFFSET;
 
   /* This is the label we will branch to if we have enough stack
-- 
2.15.1