snapshot.cc

   1 #include <inttypes.h>
   2 #include <sys/mman.h>
   3 #include <unistd.h>
   4 #include <signal.h>
   5 #include <stdlib.h>
   6 #include <map>
   7 #include <cstring>
   8 #include <cstdio>
   9 #include "snapshot.h"
  10 #include "snapshotimp.h"
  11 #include "mymemory.h"
  12 #include <fcntl.h>
  13 #include <assert.h>
  14 #include <pthread.h>
  15 #include <semaphore.h>
  16 #include <errno.h>
  17 #include <sys/wait.h>
  18 #include <ucontext.h>
  19
  20 #define FAILURE(mesg) { printf("failed in the API: %s with errno relative message: %s\n", mesg, strerror( errno ) ); exit(EXIT_FAILURE); }
  21
  22 #ifdef CONFIG_SSDEBUG
  23 #define SSDEBUG         printf
  24 #else
  25 #define SSDEBUG(...)    do { } while (0)
  26 #endif
  27
  28 /* extern declaration definition */
  29 #if USE_MPROTECT_SNAPSHOT
  30 struct SnapShot * snapshotrecord = NULL;
  31 struct Snapshot_t * sTheRecord = NULL;
  32 #else
  33 struct Snapshot_t * sTheRecord = NULL;
  34 #endif
  35
  36 #if !USE_MPROTECT_SNAPSHOT
  37 static ucontext_t savedSnapshotContext;
  38 static ucontext_t savedUserSnapshotContext;
  39 static snapshot_id snapshotid = 0;
  40 #endif
  41
  42 #if USE_MPROTECT_SNAPSHOT
  43
  44 /** The initSnapShotRecord method initialized the snapshotting data
  45  *  structures for the mprotect based snapshot.
  46  */
  47 void initSnapShotRecord(unsigned int numbackingpages, unsigned int numsnapshots, unsigned int nummemoryregions) {
  48         snapshotrecord=( struct SnapShot * )MYMALLOC(sizeof(struct SnapShot));
  49         snapshotrecord->regionsToSnapShot=( struct MemoryRegion * )MYMALLOC(sizeof(struct MemoryRegion)*nummemoryregions);
  50         snapshotrecord->backingStoreBasePtr= ( struct SnapShotPage * )MYMALLOC( sizeof( struct SnapShotPage ) * (numbackingpages + 1) );
  51         //Page align the backingstorepages
  52         snapshotrecord->backingStore=( struct SnapShotPage * )PageAlignAddressUpward(snapshotrecord->backingStoreBasePtr);
  53         snapshotrecord->backingRecords=( struct BackingPageRecord * )MYMALLOC(sizeof(struct BackingPageRecord)*numbackingpages);
  54         snapshotrecord->snapShots= ( struct SnapShotRecord * )MYMALLOC(sizeof(struct SnapShotRecord)*numsnapshots);
  55         snapshotrecord->lastSnapShot=0;
  56         snapshotrecord->lastBackingPage=0;
  57         snapshotrecord->lastRegion=0;
  58         snapshotrecord->maxRegions=nummemoryregions;
  59         snapshotrecord->maxBackingPages=numbackingpages;
  60         snapshotrecord->maxSnapShots=numsnapshots;
  61 }
  62 #endif //nothing to initialize for the fork based snapshotting.
  63
  64 /** HandlePF is the page fault handler for mprotect based snapshotting
  65  * algorithm.
  66  */
  67
  68 void HandlePF( int sig, siginfo_t *si, void * unused){
  69 #if USE_MPROTECT_SNAPSHOT
  70         if( si->si_code == SEGV_MAPERR ){
  71                 printf("Real Fault at %p\n", si->si_addr);
  72                 exit( EXIT_FAILURE );
  73         }
  74         void* addr = ReturnPageAlignedAddress(si->si_addr);
  75
  76         unsigned int backingpage=snapshotrecord->lastBackingPage++; //Could run out of pages...
  77         if (backingpage==snapshotrecord->maxBackingPages) {
  78                 printf("Out of backing pages at %p\n", si->si_addr);
  79                 exit( EXIT_FAILURE );
  80         }
  81
  82         //copy page
  83         memcpy(&(snapshotrecord->backingStore[backingpage]), addr, sizeof(struct SnapShotPage));
  84         //remember where to copy page back to
  85         snapshotrecord->backingRecords[backingpage].basePtrOfPage=addr;
  86         //set protection to read/write
  87         if (mprotect( addr, sizeof(struct SnapShotPage), PROT_READ | PROT_WRITE )) {
  88                 perror("mprotect");
  89                 // Handle error by quitting?
  90         }
  91 #endif //nothing to handle for non snapshotting case.
  92 }
  93
  94 /** ReturnPageAlignedAddress returns a page aligned address for the
  95  * address being added as a side effect the numBytes are also changed.
  96  */
  97
  98 void * ReturnPageAlignedAddress(void * addr) {
  99         return (void *)(((uintptr_t)addr)&~(PAGESIZE-1));
 100 }
 101
 102 /** PageAlignedAdressUpdate return a page aligned address for the
 103  * address being added as a side effect the numBytes are also changed.
 104  */
 105
 106 void * PageAlignAddressUpward(void * addr) {
 107         return (void *)((((uintptr_t)addr)+PAGESIZE-1)&~(PAGESIZE-1));
 108 }
 109 #ifdef __cplusplus
 110 extern "C" {
 111 #endif
 112         void createSharedLibrary(){
 113 #if !USE_MPROTECT_SNAPSHOT
 114                 //step 1. create shared memory.
 115                 if( sTheRecord ) return;
 116                 int fd = shm_open( "/ModelChecker-Snapshotter", O_RDWR | O_CREAT, 0777 ); //universal permissions.
 117                 if( -1 == fd ) FAILURE("shm_open");
 118                 if( -1 == ftruncate( fd, ( size_t )SHARED_MEMORY_DEFAULT + ( size_t )STACK_SIZE_DEFAULT ) ) FAILURE( "ftruncate" );
 119                 char * memMapBase = ( char * ) mmap( 0, ( size_t )SHARED_MEMORY_DEFAULT + ( size_t )STACK_SIZE_DEFAULT, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0 );
 120                 if( MAP_FAILED == memMapBase ) FAILURE("mmap");
 121                 sTheRecord = ( struct Snapshot_t * )memMapBase;
 122                 sTheRecord->mSharedMemoryBase = memMapBase + sizeof( struct Snapshot_t );
 123                 sTheRecord->mStackBase = ( char * )memMapBase + ( size_t )SHARED_MEMORY_DEFAULT;
 124                 sTheRecord->mStackSize = STACK_SIZE_DEFAULT;
 125                 sTheRecord->mIDToRollback = -1;
 126                 sTheRecord->currSnapShotID = 0;
 127                 sTheRecord->mbFinalize = false;
 128 #endif
 129         }
 130 #ifdef __cplusplus
 131 }
 132 #endif
 133
 134 /** The initSnapShotLibrary function initializes the Snapshot library.
 135  *  @param entryPoint the function that should run the program.
 136  */
 137 void initSnapShotLibrary(unsigned int numbackingpages,
 138                 unsigned int numsnapshots, unsigned int nummemoryregions,
 139                 unsigned int numheappages, VoidFuncPtr entryPoint) {
 140 #if USE_MPROTECT_SNAPSHOT
 141         /* Setup a stack for our signal handler....  */
 142         stack_t ss;
 143         ss.ss_sp = MYMALLOC(SIGSTACKSIZE);
 144         ss.ss_size = SIGSTACKSIZE;
 145         ss.ss_flags = 0;
 146         sigaltstack(&ss, NULL);
 147
 148         struct sigaction sa;
 149         sa.sa_flags = SA_SIGINFO | SA_NODEFER | SA_RESTART | SA_ONSTACK;
 150         sigemptyset( &sa.sa_mask );
 151         sa.sa_sigaction = HandlePF;
 152 #ifdef MAC
 153         if( sigaction( SIGBUS, &sa, NULL ) == -1 ){
 154                 printf("SIGACTION CANNOT BE INSTALLED\n");
 155                 exit(EXIT_FAILURE);
 156         }
 157 #endif
 158         if( sigaction( SIGSEGV, &sa, NULL ) == -1 ){
 159                 printf("SIGACTION CANNOT BE INSTALLED\n");
 160                 exit(EXIT_FAILURE);
 161         }
 162
 163         initSnapShotRecord(numbackingpages, numsnapshots, nummemoryregions);
 164
 165         // EVIL HACK: We need to make sure that calls into the HandlePF method don't cause dynamic links
 166         // The problem is that we end up protecting state in the dynamic linker...
 167         // Solution is to call our signal handler before we start protecting stuff...
 168
 169         siginfo_t si;
 170         memset(&si, 0, sizeof(si));
 171         si.si_addr=ss.ss_sp;
 172         HandlePF(SIGSEGV, &si, NULL);
 173         snapshotrecord->lastBackingPage--; //remove the fake page we copied
 174
 175         basemySpace=MYMALLOC((numheappages+1)*PAGESIZE);
 176         void * pagealignedbase=PageAlignAddressUpward(basemySpace);
 177         mySpace = create_mspace_with_base(pagealignedbase,  numheappages*PAGESIZE, 1 );
 178         addMemoryRegionToSnapShot(pagealignedbase, numheappages);
 179         entryPoint();
 180 #else
 181
 182         basemySpace=system_malloc((numheappages+1)*PAGESIZE);
 183         void * pagealignedbase=PageAlignAddressUpward(basemySpace);
 184         mySpace = create_mspace_with_base(pagealignedbase,  numheappages*PAGESIZE, 1 );
 185         createSharedLibrary();
 186
 187         //step 2 setup the stack context.
 188
 189         int alreadySwapped = 0;
 190         getcontext( &savedSnapshotContext );
 191         if( !alreadySwapped ){
 192                 alreadySwapped = 1;
 193                 ucontext_t currentContext, swappedContext, newContext;
 194                 getcontext( &newContext );
 195                 newContext.uc_stack.ss_sp = sTheRecord->mStackBase;
 196                 newContext.uc_stack.ss_size = STACK_SIZE_DEFAULT;
 197                 newContext.uc_link = &currentContext;
 198                 makecontext( &newContext, entryPoint, 0 );
 199                 swapcontext( &swappedContext, &newContext );
 200         }
 201
 202         //add the code to take a snapshot here...
 203         //to return to user process, do a second swapcontext...
 204         pid_t forkedID = 0;
 205         snapshotid = sTheRecord->currSnapShotID;
 206         bool swapContext = false;
 207         while( !sTheRecord->mbFinalize ){
 208                 sTheRecord->currSnapShotID=snapshotid+1;
 209                 forkedID = fork();
 210                 if( 0 == forkedID ){
 211                         ucontext_t currentContext;
 212 #if 0
 213                         int dbg = 0;
 214                         while( !dbg );
 215 #endif
 216                         if( swapContext )
 217                                 swapcontext( &currentContext, &( sTheRecord->mContextToRollback ) );
 218                         else{
 219                                 swapcontext( &currentContext, &savedUserSnapshotContext );
 220                         }
 221                 } else {
 222                         int status;
 223                         int retVal;
 224
 225                         SSDEBUG("The process id of child is %d and the process id of this process is %d and snapshot id is %d",
 226                                 forkedID, getpid(), snapshotid );
 227
 228                         do {
 229                                 retVal=waitpid( forkedID, &status, 0 );
 230                         } while( -1 == retVal && errno == EINTR );
 231
 232                         if( sTheRecord->mIDToRollback != snapshotid )
 233                                 exit(EXIT_SUCCESS);
 234                         else{
 235                                 swapContext = true;
 236                         }
 237                 }
 238         }
 239
 240 #endif
 241 }
 242
 243 /** The addMemoryRegionToSnapShot function assumes that addr is page aligned.
 244  */
 245 void addMemoryRegionToSnapShot( void * addr, unsigned int numPages) {
 246 #if USE_MPROTECT_SNAPSHOT
 247         unsigned int memoryregion=snapshotrecord->lastRegion++;
 248         if (memoryregion==snapshotrecord->maxRegions) {
 249                 printf("Exceeded supported number of memory regions!\n");
 250                 exit(EXIT_FAILURE);
 251         }
 252
 253         snapshotrecord->regionsToSnapShot[ memoryregion ].basePtr=addr;
 254         snapshotrecord->regionsToSnapShot[ memoryregion ].sizeInPages=numPages;
 255 #endif //NOT REQUIRED IN THE CASE OF FORK BASED SNAPSHOTS.
 256 }
 257
 258 /** The takeSnapshot function takes a snapshot.
 259  * @return The snapshot identifier.
 260  */
 261
 262 snapshot_id takeSnapshot( ){
 263 #if USE_MPROTECT_SNAPSHOT
 264         for(unsigned int region=0; region<snapshotrecord->lastRegion;region++) {
 265                 if( mprotect(snapshotrecord->regionsToSnapShot[region].basePtr, snapshotrecord->regionsToSnapShot[region].sizeInPages*sizeof(struct SnapShotPage), PROT_READ ) == -1 ){
 266                         perror("mprotect");
 267                         printf("Failed to mprotect inside of takeSnapShot\n");
 268                         exit(EXIT_FAILURE);
 269                 }
 270         }
 271         unsigned int snapshot=snapshotrecord->lastSnapShot++;
 272         if (snapshot==snapshotrecord->maxSnapShots) {
 273                 printf("Out of snapshots\n");
 274                 exit(EXIT_FAILURE);
 275         }
 276         snapshotrecord->snapShots[snapshot].firstBackingPage=snapshotrecord->lastBackingPage;
 277
 278         return snapshot;
 279 #else
 280         swapcontext( &savedUserSnapshotContext, &savedSnapshotContext );
 281         return snapshotid;
 282 #endif
 283 }
 284
 285 /** The rollBack function rollback to the given snapshot identifier.
 286  *  @param theID is the snapshot identifier to rollback to.
 287  */
 288
 289 void rollBack( snapshot_id theID ){
 290 #if USE_MPROTECT_SNAPSHOT
 291         std::map< void *, bool, std::less< void * >, MyAlloc< std::pair< const void *, bool > > > duplicateMap;
 292         for(unsigned int region=0; region<snapshotrecord->lastRegion;region++) {
 293                 if( mprotect(snapshotrecord->regionsToSnapShot[region].basePtr, snapshotrecord->regionsToSnapShot[region].sizeInPages*sizeof(struct SnapShotPage), PROT_READ | PROT_WRITE ) == -1 ){
 294                         perror("mprotect");
 295                         printf("Failed to mprotect inside of takeSnapShot\n");
 296                         exit(EXIT_FAILURE);
 297                 }
 298         }
 299         for(unsigned int page=snapshotrecord->snapShots[theID].firstBackingPage; page<snapshotrecord->lastBackingPage; page++) {
 300                 bool oldVal = false;
 301                 if( duplicateMap.find( snapshotrecord->backingRecords[page].basePtrOfPage ) != duplicateMap.end() ){
 302                         oldVal = true;
 303                 }
 304                 else{
 305                         duplicateMap[ snapshotrecord->backingRecords[page].basePtrOfPage ] = true;
 306                 }
 307                 if(  !oldVal ){
 308                         memcpy(snapshotrecord->backingRecords[page].basePtrOfPage, &snapshotrecord->backingStore[page], sizeof(struct SnapShotPage));
 309                 }
 310         }
 311         snapshotrecord->lastSnapShot=theID;
 312         snapshotrecord->lastBackingPage=snapshotrecord->snapShots[theID].firstBackingPage;
 313         takeSnapshot(); //Make sure current snapshot is still good...All later ones are cleared
 314 #else
 315         sTheRecord->mIDToRollback = theID;
 316         int sTemp = 0;
 317         getcontext( &sTheRecord->mContextToRollback );
 318         if( !sTemp ){
 319                 sTemp = 1;
 320                 SSDEBUG("Invoked rollback");
 321                 exit(EXIT_SUCCESS);
 322         }
 323 #endif
 324 }
 325
 326 /** The finalize method shuts down the snapshotting system.  */
 327 //Subramanian -- remove this function from the external interface and
 328 //have us call it internally
 329
 330 void finalize(){
 331 #if !USE_MPROTECT_SNAPSHOT
 332         sTheRecord->mbFinalize = true;
 333 #endif
 334 }
 335