10 #include "snapshotimp.h"
15 #include <semaphore.h>
22 #define FAILURE(mesg) { printf("failed in the API: %s with errno relative message: %s\n", mesg, strerror( errno ) ); exit(EXIT_FAILURE); }
25 #define SSDEBUG printf
27 #define SSDEBUG(...) do { } while (0)
30 /* extern declaration definition */
31 struct SnapShot * snapshotrecord = NULL;
33 #if !USE_MPROTECT_SNAPSHOT
35 * These variables are necessary because the stack is shared region and
36 * there exists a race between all processes executing the same function.
37 * To avoid the problem above, we require variables allocated in 'safe' regions.
38 * The bug was actually observed with the forkID, these variables below are
39 * used to indicate the various contexts to which to switch to.
41 * @savedSnapshotContext: contains the point to which takesnapshot() call should switch to.
42 * @savedUserSnapshotContext: contains the point to which the process whose snapshotid is equal to the rollbackid should switch to
43 * @snapshotid: it is a running counter for the various forked processes snapshotid. it is incremented and set in a persistently shared record
45 static ucontext_t savedSnapshotContext;
46 static ucontext_t savedUserSnapshotContext;
47 static snapshot_id snapshotid = 0;
49 #else /* USE_MPROTECT_SNAPSHOT */
51 /** PageAlignedAdressUpdate return a page aligned address for the
52 * address being added as a side effect the numBytes are also changed.
54 static void * PageAlignAddressUpward(void * addr) {
55 return (void *)((((uintptr_t)addr)+PAGESIZE-1)&~(PAGESIZE-1));
58 /** ReturnPageAlignedAddress returns a page aligned address for the
59 * address being added as a side effect the numBytes are also changed.
61 static void * ReturnPageAlignedAddress(void * addr) {
62 return (void *)(((uintptr_t)addr)&~(PAGESIZE-1));
65 /** The initSnapShotRecord method initialized the snapshotting data
66 * structures for the mprotect based snapshot.
68 static void initSnapShotRecord(unsigned int numbackingpages, unsigned int numsnapshots, unsigned int nummemoryregions) {
69 snapshotrecord=( struct SnapShot * )model_malloc(sizeof(struct SnapShot));
70 snapshotrecord->regionsToSnapShot=( struct MemoryRegion * )model_malloc(sizeof(struct MemoryRegion)*nummemoryregions);
71 snapshotrecord->backingStoreBasePtr= ( struct SnapShotPage * )model_malloc( sizeof( struct SnapShotPage ) * (numbackingpages + 1) );
72 //Page align the backingstorepages
73 snapshotrecord->backingStore=( struct SnapShotPage * )PageAlignAddressUpward(snapshotrecord->backingStoreBasePtr);
74 snapshotrecord->backingRecords=( struct BackingPageRecord * )model_malloc(sizeof(struct BackingPageRecord)*numbackingpages);
75 snapshotrecord->snapShots= ( struct SnapShotRecord * )model_malloc(sizeof(struct SnapShotRecord)*numsnapshots);
76 snapshotrecord->lastSnapShot=0;
77 snapshotrecord->lastBackingPage=0;
78 snapshotrecord->lastRegion=0;
79 snapshotrecord->maxRegions=nummemoryregions;
80 snapshotrecord->maxBackingPages=numbackingpages;
81 snapshotrecord->maxSnapShots=numsnapshots;
84 /** HandlePF is the page fault handler for mprotect based snapshotting
87 static void HandlePF( int sig, siginfo_t *si, void * unused){
88 if( si->si_code == SEGV_MAPERR ){
89 printf("Real Fault at %p\n", si->si_addr);
93 void* addr = ReturnPageAlignedAddress(si->si_addr);
95 unsigned int backingpage=snapshotrecord->lastBackingPage++; //Could run out of pages...
96 if (backingpage==snapshotrecord->maxBackingPages) {
97 printf("Out of backing pages at %p\n", si->si_addr);
102 memcpy(&(snapshotrecord->backingStore[backingpage]), addr, sizeof(struct SnapShotPage));
103 //remember where to copy page back to
104 snapshotrecord->backingRecords[backingpage].basePtrOfPage=addr;
105 //set protection to read/write
106 if (mprotect( addr, sizeof(struct SnapShotPage), PROT_READ | PROT_WRITE )) {
108 // Handle error by quitting?
111 #endif /* USE_MPROTECT_SNAPSHOT */
113 #if !USE_MPROTECT_SNAPSHOT
114 void createSharedMemory(){
115 //step 1. create shared memory.
116 void * memMapBase = mmap( 0, SHARED_MEMORY_DEFAULT + STACK_SIZE_DEFAULT, PROT_READ | PROT_WRITE, MAP_SHARED|MAP_ANON, -1, 0 );
117 if( MAP_FAILED == memMapBase )
120 //Setup snapshot record at top of free region
121 snapshotrecord = ( struct SnapShot * )memMapBase;
122 snapshotrecord->mSharedMemoryBase = (void *)((uintptr_t)memMapBase + sizeof(struct SnapShot));
123 snapshotrecord->mStackBase = (void *)((uintptr_t)memMapBase + SHARED_MEMORY_DEFAULT);
124 snapshotrecord->mStackSize = STACK_SIZE_DEFAULT;
125 snapshotrecord->mIDToRollback = -1;
126 snapshotrecord->currSnapShotID = 0;
131 /** The initSnapshotLibrary function initializes the snapshot library.
132 * @param entryPoint the function that should run the program.
134 #if USE_MPROTECT_SNAPSHOT
136 void initSnapshotLibrary(unsigned int numbackingpages,
137 unsigned int numsnapshots, unsigned int nummemoryregions,
138 unsigned int numheappages, VoidFuncPtr entryPoint) {
139 /* Setup a stack for our signal handler.... */
141 ss.ss_sp = PageAlignAddressUpward(model_malloc(SIGSTACKSIZE+PAGESIZE-1));
142 ss.ss_size = SIGSTACKSIZE;
144 sigaltstack(&ss, NULL);
147 sa.sa_flags = SA_SIGINFO | SA_NODEFER | SA_RESTART | SA_ONSTACK;
148 sigemptyset( &sa.sa_mask );
149 sa.sa_sigaction = HandlePF;
151 if( sigaction( SIGBUS, &sa, NULL ) == -1 ){
152 printf("SIGACTION CANNOT BE INSTALLED\n");
156 if( sigaction( SIGSEGV, &sa, NULL ) == -1 ){
157 printf("SIGACTION CANNOT BE INSTALLED\n");
161 initSnapShotRecord(numbackingpages, numsnapshots, nummemoryregions);
163 // EVIL HACK: We need to make sure that calls into the HandlePF method don't cause dynamic links
164 // The problem is that we end up protecting state in the dynamic linker...
165 // Solution is to call our signal handler before we start protecting stuff...
168 memset(&si, 0, sizeof(si));
170 HandlePF(SIGSEGV, &si, NULL);
171 snapshotrecord->lastBackingPage--; //remove the fake page we copied
173 void *basemySpace = model_malloc((numheappages+1)*PAGESIZE);
174 void * pagealignedbase=PageAlignAddressUpward(basemySpace);
175 user_snapshot_space = create_mspace_with_base(pagealignedbase, numheappages * PAGESIZE, 1);
176 addMemoryRegionToSnapShot(pagealignedbase, numheappages);
180 void initSnapshotLibrary(unsigned int numbackingpages,
181 unsigned int numsnapshots, unsigned int nummemoryregions,
182 unsigned int numheappages, VoidFuncPtr entryPoint) {
184 createSharedMemory();
186 //step 2 setup the stack context.
187 ucontext_t newContext;
188 getcontext( &newContext );
189 newContext.uc_stack.ss_sp = snapshotrecord->mStackBase;
190 newContext.uc_stack.ss_size = STACK_SIZE_DEFAULT;
191 makecontext( &newContext, entryPoint, 0 );
192 /* switch to a new entryPoint context, on a new stack */
193 swapcontext(&savedSnapshotContext, &newContext);
195 /* switch back here when takesnapshot is called */
197 snapshotid = snapshotrecord->currSnapShotID;
198 /* This bool indicates that the current process's snapshotid is same
199 as the id to which the rollback needs to occur */
201 bool rollback = false;
203 snapshotrecord->currSnapShotID=snapshotid+1;
207 /* If the rollback bool is set, switch to the context we need to
208 return to during a rollback. */
210 setcontext( &( snapshotrecord->mContextToRollback ) );
212 /*Child process which is forked as a result of takesnapshot
213 call should switch back to the takesnapshot context*/
214 setcontext( &savedUserSnapshotContext );
220 SSDEBUG("The process id of child is %d and the process id of this process is %d and snapshot id is %d\n",
221 forkedID, getpid(), snapshotid );
224 retVal=waitpid( forkedID, &status, 0 );
225 } while( -1 == retVal && errno == EINTR );
227 if( snapshotrecord->mIDToRollback != snapshotid ) {
236 /** The addMemoryRegionToSnapShot function assumes that addr is page aligned.
238 void addMemoryRegionToSnapShot( void * addr, unsigned int numPages) {
239 #if USE_MPROTECT_SNAPSHOT
240 unsigned int memoryregion=snapshotrecord->lastRegion++;
241 if (memoryregion==snapshotrecord->maxRegions) {
242 printf("Exceeded supported number of memory regions!\n");
246 snapshotrecord->regionsToSnapShot[ memoryregion ].basePtr=addr;
247 snapshotrecord->regionsToSnapShot[ memoryregion ].sizeInPages=numPages;
248 #endif //NOT REQUIRED IN THE CASE OF FORK BASED SNAPSHOTS.
251 /** The takeSnapshot function takes a snapshot.
252 * @return The snapshot identifier.
254 snapshot_id takeSnapshot( ){
255 #if USE_MPROTECT_SNAPSHOT
256 for(unsigned int region=0; region<snapshotrecord->lastRegion;region++) {
257 if( mprotect(snapshotrecord->regionsToSnapShot[region].basePtr, snapshotrecord->regionsToSnapShot[region].sizeInPages*sizeof(struct SnapShotPage), PROT_READ ) == -1 ){
259 printf("Failed to mprotect inside of takeSnapShot\n");
263 unsigned int snapshot=snapshotrecord->lastSnapShot++;
264 if (snapshot==snapshotrecord->maxSnapShots) {
265 printf("Out of snapshots\n");
268 snapshotrecord->snapShots[snapshot].firstBackingPage=snapshotrecord->lastBackingPage;
272 swapcontext( &savedUserSnapshotContext, &savedSnapshotContext );
273 SSDEBUG("TAKESNAPSHOT RETURN\n");
278 /** The rollBack function rollback to the given snapshot identifier.
279 * @param theID is the snapshot identifier to rollback to.
281 void rollBack( snapshot_id theID ){
282 #if USE_MPROTECT_SNAPSHOT==2
283 if (snapshotrecord->lastSnapShot==(theID+1)) {
284 for(unsigned int page=snapshotrecord->snapShots[theID].firstBackingPage; page<snapshotrecord->lastBackingPage; page++) {
285 memcpy(snapshotrecord->backingRecords[page].basePtrOfPage, &snapshotrecord->backingStore[page], sizeof(struct SnapShotPage));
291 #if USE_MPROTECT_SNAPSHOT
292 HashTable< void *, bool, uintptr_t, 4, model_malloc, model_calloc, model_free> duplicateMap;
293 for(unsigned int region=0; region<snapshotrecord->lastRegion;region++) {
294 if( mprotect(snapshotrecord->regionsToSnapShot[region].basePtr, snapshotrecord->regionsToSnapShot[region].sizeInPages*sizeof(struct SnapShotPage), PROT_READ | PROT_WRITE ) == -1 ){
296 printf("Failed to mprotect inside of takeSnapShot\n");
300 for(unsigned int page=snapshotrecord->snapShots[theID].firstBackingPage; page<snapshotrecord->lastBackingPage; page++) {
301 if( !duplicateMap.contains(snapshotrecord->backingRecords[page].basePtrOfPage )) {
302 duplicateMap.put(snapshotrecord->backingRecords[page].basePtrOfPage, true);
303 memcpy(snapshotrecord->backingRecords[page].basePtrOfPage, &snapshotrecord->backingStore[page], sizeof(struct SnapShotPage));
306 snapshotrecord->lastSnapShot=theID;
307 snapshotrecord->lastBackingPage=snapshotrecord->snapShots[theID].firstBackingPage;
308 takeSnapshot(); //Make sure current snapshot is still good...All later ones are cleared
310 snapshotrecord->mIDToRollback = theID;
311 volatile int sTemp = 0;
312 getcontext( &snapshotrecord->mContextToRollback );
314 * This is used to quit the process on rollback, so that the process
315 * which needs to rollback can quit allowing the process whose
316 * snapshotid matches the rollbackid to switch to this context and
321 SSDEBUG("Invoked rollback\n");
325 * This fix obviates the need for a finalize call. hence less dependences for model-checker....
328 snapshotrecord->mIDToRollback = -1;