10 #include "hashtable.h"
17 /** PageAlignedAdressUpdate return a page aligned address for the
18 * address being added as a side effect the numBytes are also changed.
20 static void * PageAlignAddressUpward(void *addr)
22 return (void *)((((uintptr_t)addr) + PAGESIZE - 1) & ~(PAGESIZE - 1));
25 #if USE_MPROTECT_SNAPSHOT
27 /* Each SnapShotRecord lists the firstbackingpage that must be written to
28 * revert to that snapshot */
29 struct SnapShotRecord {
30 unsigned int firstBackingPage;
33 /** @brief Backing store page */
34 typedef unsigned char snapshot_page_t[PAGESIZE];
36 /* List the base address of the corresponding page in the backing store so we
37 * know where to copy it to */
38 struct BackingPageRecord {
42 /* Struct for each memory region */
44 void *basePtr; // base of memory region
45 int sizeInPages; // size of memory region in pages
48 /** ReturnPageAlignedAddress returns a page aligned address for the
49 * address being added as a side effect the numBytes are also changed.
51 static void * ReturnPageAlignedAddress(void *addr)
53 return (void *)(((uintptr_t)addr) & ~(PAGESIZE - 1));
56 /* Primary struct for snapshotting system */
57 struct mprot_snapshotter {
58 mprot_snapshotter(unsigned int numbackingpages, unsigned int numsnapshots, unsigned int nummemoryregions);
61 struct MemoryRegion *regionsToSnapShot; //This pointer references an array of memory regions to snapshot
62 snapshot_page_t *backingStore; //This pointer references an array of snapshotpage's that form the backing store
63 void *backingStoreBasePtr; //This pointer references an array of snapshotpage's that form the backing store
64 struct BackingPageRecord *backingRecords; //This pointer references an array of backingpagerecord's (same number of elements as backingstore
65 struct SnapShotRecord *snapShots; //This pointer references the snapshot array
67 unsigned int lastSnapShot; //Stores the next snapshot record we should use
68 unsigned int lastBackingPage; //Stores the next backingpage we should use
69 unsigned int lastRegion; //Stores the next memory region to be used
71 unsigned int maxRegions; //Stores the max number of memory regions we support
72 unsigned int maxBackingPages; //Stores the total number of backing pages
73 unsigned int maxSnapShots; //Stores the total number of snapshots we allow
78 static struct mprot_snapshotter *mprot_snap = NULL;
80 mprot_snapshotter::mprot_snapshotter(unsigned int backing_pages, unsigned int snapshots, unsigned int regions) :
85 maxBackingPages(backing_pages),
86 maxSnapShots(snapshots)
88 regionsToSnapShot = (struct MemoryRegion *)model_malloc(sizeof(struct MemoryRegion) * regions);
89 backingStoreBasePtr = (void *)model_malloc(sizeof(snapshot_page_t) * (backing_pages + 1));
90 //Page align the backingstorepages
91 backingStore = (snapshot_page_t *)PageAlignAddressUpward(backingStoreBasePtr);
92 backingRecords = (struct BackingPageRecord *)model_malloc(sizeof(struct BackingPageRecord) * backing_pages);
93 snapShots = (struct SnapShotRecord *)model_malloc(sizeof(struct SnapShotRecord) * snapshots);
96 mprot_snapshotter::~mprot_snapshotter()
98 model_free(regionsToSnapShot);
99 model_free(backingStoreBasePtr);
100 model_free(backingRecords);
101 model_free(snapShots);
104 /** mprot_handle_pf is the page fault handler for mprotect based snapshotting
107 static void mprot_handle_pf(int sig, siginfo_t *si, void *unused)
109 if (si->si_code == SEGV_MAPERR) {
110 model_print("Segmentation fault at %p\n", si->si_addr);
111 model_print("For debugging, place breakpoint at: %s:%d\n",
113 // print_trace(); // Trace printing may cause dynamic memory allocation
116 void* addr = ReturnPageAlignedAddress(si->si_addr);
118 unsigned int backingpage = mprot_snap->lastBackingPage++; //Could run out of pages...
119 if (backingpage == mprot_snap->maxBackingPages) {
120 model_print("Out of backing pages at %p\n", si->si_addr);
125 memcpy(&(mprot_snap->backingStore[backingpage]), addr, sizeof(snapshot_page_t));
126 //remember where to copy page back to
127 mprot_snap->backingRecords[backingpage].basePtrOfPage = addr;
128 //set protection to read/write
129 if (mprotect(addr, sizeof(snapshot_page_t), PROT_READ | PROT_WRITE)) {
131 // Handle error by quitting?
135 static void mprot_snapshot_init(unsigned int numbackingpages,
136 unsigned int numsnapshots, unsigned int nummemoryregions,
137 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 = mprot_handle_pf;
151 if (sigaction(SIGBUS, &sa, NULL) == -1) {
152 perror("sigaction(SIGBUS)");
156 if (sigaction(SIGSEGV, &sa, NULL) == -1) {
157 perror("sigaction(SIGSEGV)");
161 mprot_snap = new mprot_snapshotter(numbackingpages, numsnapshots, nummemoryregions);
163 // EVIL HACK: We need to make sure that calls into the mprot_handle_pf 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));
169 si.si_addr = ss.ss_sp;
170 mprot_handle_pf(SIGSEGV, &si, NULL);
171 mprot_snap->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 snapshot_add_memory_region(pagealignedbase, numheappages);
178 void *base_model_snapshot_space = model_malloc((numheappages + 1) * PAGESIZE);
179 pagealignedbase = PageAlignAddressUpward(base_model_snapshot_space);
180 model_snapshot_space = create_mspace_with_base(pagealignedbase, numheappages * PAGESIZE, 1);
181 snapshot_add_memory_region(pagealignedbase, numheappages);
186 static void mprot_add_to_snapshot(void *addr, unsigned int numPages)
188 unsigned int memoryregion = mprot_snap->lastRegion++;
189 if (memoryregion == mprot_snap->maxRegions) {
190 model_print("Exceeded supported number of memory regions!\n");
194 DEBUG("snapshot region %p-%p (%u page%s)\n",
195 addr, (char *)addr + numPages * PAGESIZE, numPages,
196 numPages > 1 ? "s" : "");
197 mprot_snap->regionsToSnapShot[memoryregion].basePtr = addr;
198 mprot_snap->regionsToSnapShot[memoryregion].sizeInPages = numPages;
201 static snapshot_id mprot_take_snapshot()
203 for (unsigned int region = 0;region < mprot_snap->lastRegion;region++) {
204 if (mprotect(mprot_snap->regionsToSnapShot[region].basePtr, mprot_snap->regionsToSnapShot[region].sizeInPages * sizeof(snapshot_page_t), PROT_READ) == -1) {
206 model_print("Failed to mprotect inside of takeSnapShot\n");
210 unsigned int snapshot = mprot_snap->lastSnapShot++;
211 if (snapshot == mprot_snap->maxSnapShots) {
212 model_print("Out of snapshots\n");
215 mprot_snap->snapShots[snapshot].firstBackingPage = mprot_snap->lastBackingPage;
220 static void mprot_roll_back(snapshot_id theID)
222 #if USE_MPROTECT_SNAPSHOT == 2
223 if (mprot_snap->lastSnapShot == (theID + 1)) {
224 for (unsigned int page = mprot_snap->snapShots[theID].firstBackingPage;page < mprot_snap->lastBackingPage;page++) {
225 memcpy(mprot_snap->backingRecords[page].basePtrOfPage, &mprot_snap->backingStore[page], sizeof(snapshot_page_t));
231 HashTable< void *, bool, uintptr_t, 4, model_malloc, model_calloc, model_free> duplicateMap;
232 for (unsigned int region = 0;region < mprot_snap->lastRegion;region++) {
233 if (mprotect(mprot_snap->regionsToSnapShot[region].basePtr, mprot_snap->regionsToSnapShot[region].sizeInPages * sizeof(snapshot_page_t), PROT_READ | PROT_WRITE) == -1) {
235 model_print("Failed to mprotect inside of takeSnapShot\n");
239 for (unsigned int page = mprot_snap->snapShots[theID].firstBackingPage;page < mprot_snap->lastBackingPage;page++) {
240 if (!duplicateMap.contains(mprot_snap->backingRecords[page].basePtrOfPage)) {
241 duplicateMap.put(mprot_snap->backingRecords[page].basePtrOfPage, true);
242 memcpy(mprot_snap->backingRecords[page].basePtrOfPage, &mprot_snap->backingStore[page], sizeof(snapshot_page_t));
245 mprot_snap->lastSnapShot = theID;
246 mprot_snap->lastBackingPage = mprot_snap->snapShots[theID].firstBackingPage;
247 mprot_take_snapshot(); //Make sure current snapshot is still good...All later ones are cleared
250 #else /* !USE_MPROTECT_SNAPSHOT */
252 #define SHARED_MEMORY_DEFAULT (200 * ((size_t)1 << 20)) // 100mb for the shared memory
253 #define STACK_SIZE_DEFAULT (((size_t)1 << 20) * 20) // 20 mb out of the above 100 mb for my stack
255 struct fork_snapshotter {
256 /** @brief Pointer to the shared (non-snapshot) memory heap base
257 * (NOTE: this has size SHARED_MEMORY_DEFAULT - sizeof(*fork_snap)) */
258 void *mSharedMemoryBase;
260 /** @brief Pointer to the shared (non-snapshot) stack region */
263 /** @brief Size of the shared stack */
267 * @brief Stores the ID that we are attempting to roll back to
269 * Used in inter-process communication so that each process can
270 * determine whether or not to take over execution (w/ matching ID) or
271 * exit (we're rolling back even further). Dubiously marked 'volatile'
272 * to prevent compiler optimizations from messing with the
273 * inter-process behavior.
275 volatile snapshot_id mIDToRollback;
278 * @brief The context for the shared (non-snapshot) stack
280 * This context is passed between the various processes which represent
281 * various snapshot states. It should be used primarily for the
282 * "client-side" code, not the main snapshot loop.
284 ucontext_t shared_ctxt;
286 /** @brief Inter-process tracking of the next snapshot ID */
287 snapshot_id currSnapShotID;
290 static struct fork_snapshotter *fork_snap = NULL;
293 * These variables are necessary because the stack is shared region and
294 * there exists a race between all processes executing the same function.
295 * To avoid the problem above, we require variables allocated in 'safe' regions.
296 * The bug was actually observed with the forkID, these variables below are
297 * used to indicate the various contexts to which to switch to.
299 * @private_ctxt: the context which is internal to the current process. Used
300 * for running the internal snapshot/rollback loop.
301 * @exit_ctxt: a special context used just for exiting from a process (so we
302 * can use swapcontext() instead of setcontext() + hacks)
303 * @snapshotid: it is a running counter for the various forked processes
304 * snapshotid. it is incremented and set in a persistently shared record
306 static ucontext_t private_ctxt;
307 static ucontext_t exit_ctxt;
308 static snapshot_id snapshotid = 0;
311 * @brief Create a new context, with a given stack and entry function
312 * @param ctxt The context structure to fill
313 * @param stack The stack to run the new context in
314 * @param stacksize The size of the stack
315 * @param func The entry point function for the context
317 static void create_context(ucontext_t *ctxt, void *stack, size_t stacksize,
321 ctxt->uc_stack.ss_sp = stack;
322 ctxt->uc_stack.ss_size = stacksize;
323 makecontext(ctxt, func, 0);
326 /** @brief An empty function, used for an "empty" context which just exits a
328 static void fork_exit()
330 /* Intentionally empty */
333 static void createSharedMemory()
335 //step 1. create shared memory.
336 void *memMapBase = mmap(0, SHARED_MEMORY_DEFAULT + STACK_SIZE_DEFAULT, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANON, -1, 0);
337 if (memMapBase == MAP_FAILED) {
342 //Setup snapshot record at top of free region
343 fork_snap = (struct fork_snapshotter *)memMapBase;
344 fork_snap->mSharedMemoryBase = (void *)((uintptr_t)memMapBase + sizeof(*fork_snap));
345 fork_snap->mStackBase = (void *)((uintptr_t)memMapBase + SHARED_MEMORY_DEFAULT);
346 fork_snap->mStackSize = STACK_SIZE_DEFAULT;
347 fork_snap->mIDToRollback = -1;
348 fork_snap->currSnapShotID = 0;
352 * Create a new mspace pointer for the non-snapshotting (i.e., inter-process
353 * shared) memory region. Only for fork-based snapshotting.
355 * @return The shared memory mspace
357 mspace create_shared_mspace()
360 createSharedMemory();
361 return create_mspace_with_base((void *)(fork_snap->mSharedMemoryBase), SHARED_MEMORY_DEFAULT - sizeof(*fork_snap), 1);
364 static void fork_snapshot_init(unsigned int numbackingpages,
365 unsigned int numsnapshots, unsigned int nummemoryregions,
366 unsigned int numheappages, VoidFuncPtr entryPoint)
369 createSharedMemory();
371 void *base_model_snapshot_space = malloc((numheappages + 1) * PAGESIZE);
372 void *pagealignedbase = PageAlignAddressUpward(base_model_snapshot_space);
373 model_snapshot_space = create_mspace_with_base(pagealignedbase, numheappages * PAGESIZE, 1);
375 /* setup an "exiting" context */
377 create_context(&exit_ctxt, stack, sizeof(stack), fork_exit);
379 /* setup the shared-stack context */
380 create_context(&fork_snap->shared_ctxt, fork_snap->mStackBase,
381 STACK_SIZE_DEFAULT, entryPoint);
382 /* switch to a new entryPoint context, on a new stack */
383 model_swapcontext(&private_ctxt, &fork_snap->shared_ctxt);
385 /* switch back here when takesnapshot is called */
386 snapshotid = fork_snap->currSnapShotID;
387 if (model->params.nofork) {
388 setcontext(&fork_snap->shared_ctxt);
394 fork_snap->currSnapShotID = snapshotid + 1;
398 setcontext(&fork_snap->shared_ctxt);
400 DEBUG("parent PID: %d, child PID: %d, snapshot ID: %d\n",
401 getpid(), forkedID, snapshotid);
403 while (waitpid(forkedID, NULL, 0) < 0) {
404 /* waitpid() may be interrupted */
405 if (errno != EINTR) {
411 if (fork_snap->mIDToRollback != snapshotid)
417 static snapshot_id fork_take_snapshot()
419 model_swapcontext(&fork_snap->shared_ctxt, &private_ctxt);
420 DEBUG("TAKESNAPSHOT RETURN\n");
424 static void fork_roll_back(snapshot_id theID)
427 fork_snap->mIDToRollback = theID;
428 model_swapcontext(&fork_snap->shared_ctxt, &exit_ctxt);
429 fork_snap->mIDToRollback = -1;
432 #endif /* !USE_MPROTECT_SNAPSHOT */
435 * @brief Initializes the snapshot system
436 * @param entryPoint the function that should run the program.
438 void snapshot_system_init(unsigned int numbackingpages,
439 unsigned int numsnapshots, unsigned int nummemoryregions,
440 unsigned int numheappages, VoidFuncPtr entryPoint)
442 #if USE_MPROTECT_SNAPSHOT
443 mprot_snapshot_init(numbackingpages, numsnapshots, nummemoryregions, numheappages, entryPoint);
445 fork_snapshot_init(numbackingpages, numsnapshots, nummemoryregions, numheappages, entryPoint);
449 /** Assumes that addr is page aligned. */
450 void snapshot_add_memory_region(void *addr, unsigned int numPages)
452 #if USE_MPROTECT_SNAPSHOT
453 mprot_add_to_snapshot(addr, numPages);
455 /* not needed for fork-based snapshotting */
459 /** Takes a snapshot of memory.
460 * @return The snapshot identifier.
462 snapshot_id take_snapshot()
464 #if USE_MPROTECT_SNAPSHOT
465 return mprot_take_snapshot();
467 return fork_take_snapshot();
471 /** Rolls the memory state back to the given snapshot identifier.
472 * @param theID is the snapshot identifier to rollback to.
474 void snapshot_roll_back(snapshot_id theID)
476 #if USE_MPROTECT_SNAPSHOT
477 mprot_roll_back(theID);
479 fork_roll_back(theID);