[MANA-78] vdso was not restored properly on CentOS 7

The reason is we saved temporary vvar&vdso address in global variable, the address of which could have been changed.

This is not a problem when vdso label is carried after mremap, but on CentOS 7, the label was missing which resulted in we umapped the temporary vdso segment and won't map vdso back

Author: jungan

src/mtcp/mtcp_header.h

@@ -101,6 +101,8 @@ typedef struct RestoreInfo {
 #endif
   MYINFO_GS_T myinfo_gs;
   int mtcp_restart_pause;  // Used by env. var. DMTCP_RESTART_PAUSE0
+  VA vvarStartTmp;
+  VA vdsoStartTmp;
   const char *restart_dir; // Directory to search for checkpoint files
 } RestoreInfo;
 

src/mtcp/mtcp_restart.c

@@ -512,7 +512,7 @@ uint64_t vdsoStartTmp = 0;
 static void
 remap_vdso_and_vvar_regions() {
   Area area;
-  int rc = 0;
+  void *rc = 0;
   uint64_t vvarStart = 0;
   uint64_t vdsoStart = 0;
   uint64_t vvarSize = 0;
@@ -543,7 +543,10 @@ remap_vdso_and_vvar_regions() {
 
   while (mtcp_readmapsline(mapsfd, &area)) {
     if (prev_addr + vvarSize + vdsoSize <= area.addr) {
-      vvarStartTmp = prev_addr;
+      if (vvarSize > 0) {
+        /* some kernel doesn't have vvar */
+        vvarStartTmp = prev_addr;
+      }
       vdsoStartTmp = prev_addr + vvarSize;
       break;
     } else {
@@ -1104,6 +1107,10 @@ restart_fast_path()
 
   DPRINTF("We have copied mtcp_restart to higher address.  We will now\n"
           "    jump into a copy of restorememoryareas().\n");
+  rinfo.vvarStartTmp = vvarStartTmp;
+  rinfo.vdsoStartTmp = vdsoStartTmp;
+  DPRINTF("%p %p %p %p\n", &vvarStartTmp, vvarStartTmp, &vdsoStartTmp, vdsoStartTmp);
+  /* after calling the following assembly, the address of vvarStartTmp & vdsoStartTmp changed */
 
 #if defined(__i386__) || defined(__x86_64__)
   asm volatile (CLEAN_FOR_64_BIT(mov %0, %%esp; )
@@ -1221,6 +1228,8 @@ restorememoryareas(RestoreInfo *rinfo_ptr, LowerHalfInfo_t *linfo_ptr)
 {
   int mtcp_sys_errno;
 
+  /* the address has been changed, the values become 0 */
+  DPRINTF("%p %p %p %p\n", &vvarStartTmp, vvarStartTmp, &vdsoStartTmp, vdsoStartTmp);
   DPRINTF("Entering copy of restorememoryareas().  Will now unmap old memory"
           "\n    and restore memory sections from the checkpoint image.\n");
 
@@ -1374,14 +1383,14 @@ unmap_memory_areas_and_restore_vdso(RestoreInfo *rinfo, LowerHalfInfo_t *lh_info
   /* Unmap everything except this image, vdso, vvar and vsyscall. */
   int mtcp_sys_errno;
   Area area;
-#if LINUX_VERSION_CODE > KERNEL_VERSION(3, 10, 0) 
+#if LINUX_VERSION_CODE > KERNEL_VERSION(3, 10, 0)
   VA vdsoStart = NULL;
   VA vdsoEnd = NULL;
 #else
   // This Linux kernel does not re-label vdso/vvar after calling mremap on it.
   // So, lower down, we will fail to find vdeso in /proc/self/maps
-  VA vdsoStart = (VA)vdsoStartTmp;
-  VA vdsoEnd = (VA)(vdsoStartTmp + 2*PAGESIZE);
+  VA vdsoStart = (VA)rinfo->vdsoStartTmp;
+  VA vdsoEnd = (VA)(rinfo->vdsoStartTmp + 2 * PAGESIZE);
 #endif
   VA vvarStart = NULL;
   VA vvarEnd = NULL;
@@ -1396,8 +1405,8 @@ unmap_memory_areas_and_restore_vdso(RestoreInfo *rinfo, LowerHalfInfo_t *lh_info
   // We create local copies of these, as they reside on the data section of
   // mtcp_restart, which is unmapped later on.
 
-  uint64_t vdsoStartTmpCopy = vdsoStartTmp;
-  uint64_t vvarStartTmpCopy = vvarStartTmp;
+  uint64_t vdsoStartTmpCopy = rinfo->vdsoStartTmp;
+  uint64_t vvarStartTmpCopy = rinfo->vvarStartTmp;
 
   while (mtcp_readmapsline(mapsfd, &area)) {
     if (area.addr >= rinfo->restore_addr && area.addr < rinfo->restore_end) {