svn commit: r321922 - head/sys/amd64/amd64

[Mateusz Guzik]

Author: mjg
Date: Wed Aug  2 11:25:38 2017
New Revision: 321922
URL: https://svnweb.freebsd.org/changeset/base/321922

Log:
  amd64: annotate the syscall return address check with __predict_false
  
  before:
     0xffffffff80b03ebb <+2059>:	mov    0x460(%r14),%rax
     0xffffffff80b03ec2 <+2066>:	mov    0x98(%rax),%rax
     0xffffffff80b03ec9 <+2073>:	shr    $0x2f,%rax
     0xffffffff80b03ecd <+2077>:	je     0xffffffff80b03edd <amd64_syscall+2093>
     0xffffffff80b03ecf <+2079>:	mov    0x3f8(%r14),%rax
     0xffffffff80b03ed6 <+2086>:	orl    $0x1,0xc8(%rax)
     0xffffffff80b03edd <+2093>:	add    $0xf8,%rsp
  
  after:
     0xffffffff80b03ebb <+2059>:	mov    0x460(%r14),%rax
     0xffffffff80b03ec2 <+2066>:	mov    0x98(%rax),%rax
     0xffffffff80b03ec9 <+2073>:	shr    $0x2f,%rax
     0xffffffff80b03ecd <+2077>:	jne    0xffffffff80b03eef <amd64_syscall+2111>
     0xffffffff80b03ecf <+2079>:	add    $0xf8,%rsp
  
  Reviewed by:	kib
  MFC after:	1 week

Modified:
  head/sys/amd64/amd64/trap.c

Modified: head/sys/amd64/amd64/trap.c
==============================================================================
--- head/sys/amd64/amd64/trap.c	Wed Aug  2 10:33:47 2017	(r321921)
+++ head/sys/amd64/amd64/trap.c	Wed Aug  2 11:25:38 2017	(r321922)
@@ -935,6 +935,6 @@ amd64_syscall(struct thread *td, int traced)
 	 * not be safe.  Instead, use the full return path which
 	 * catches the problem safely.
 	 */
-	if (td->td_frame->tf_rip >= VM_MAXUSER_ADDRESS)
+	if (__predict_false(td->td_frame->tf_rip >= VM_MAXUSER_ADDRESS))
 		set_pcb_flags(td->td_pcb, PCB_FULL_IRET);
 }