Add logic for patching calls to the x86-64 vsyscall page

tests/test_patching_input.S

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <asm/unistd.h>
 
 
         // This performs a system call directly so that we can test
         // patching this instruction sequence.
 
         .global my_getpid
         .global my_getpid_end
 my_getpid:
         mov $__NR_getpid, %eax
 #if defined(__x86_64__)
         syscall
 #elif defined(__i386__)
         int $0x80
 #else
 # error Unsupported target platform
 #endif
         ret
 my_getpid_end:
 
+
+        // These routines call the vsyscall page, which is present on
+        // x86-64 only.
+
+#if defined(__x86_64__)
+
+        .global my_vgettimeofday
+        .global my_vgettimeofday_end
+my_vgettimeofday:
+        sub $8, %rsp  // Align the stack
+        mov $0xffffffffff600000, %rax
+        call *%rax
+        add $8, %rsp
+        ret
+my_vgettimeofday_end:
+
+        .global my_vtime
+        .global my_vtime_end
+my_vtime:
+        sub $8, %rsp  // Align the stack
+        mov $0xffffffffff600400, %rax
+        call *%rax
+        add $8, %rsp
+        ret
+my_vtime_end:
+
+        .global my_vgetcpu
+        .global my_vgetcpu_end
+my_vgetcpu:
+        sub $8, %rsp  // Align the stack
+        mov $0xffffffffff600800, %rax
+        call *%rax
+        add $8, %rsp
+        ret
+my_vgetcpu_end:
+
+#endif
+
         // Tell Linux not to disable no-execute protection for the process.
         .section .note.GNU-stack,"",@progbits