X-Git-Url: http://plrg.eecs.uci.edu/git/?p=c11tester.git;a=blobdiff_plain;f=snapshot.cc;h=1f0cf352d2e214c0e5218818addb29fab2a37330;hp=5069a1cf1147cb7afb07035cbf607c69daa2c284;hb=7742256df627848c1c375f979f5369a45c92057b;hpb=d775a7d6624fa14284c4a273d039bedd21a1f55c

diff --git a/snapshot.cc b/snapshot.cc
index 5069a1cf..1f0cf352 100644
--- a/snapshot.cc
+++ b/snapshot.cc
@@ -12,268 +12,84 @@
 #include "mymemory.h"
 #include "common.h"
 #include "context.h"
+#include "model.h"
 
-/** PageAlignedAdressUpdate return a page aligned address for the
- * address being added as a side effect the numBytes are also changed.
- */
-static void * PageAlignAddressUpward(void *addr)
-{
-	return (void *)((((uintptr_t)addr) + PAGESIZE - 1) & ~(PAGESIZE - 1));
-}
-
-#if USE_MPROTECT_SNAPSHOT
-
-/* Each SnapShotRecord lists the firstbackingpage that must be written to
- * revert to that snapshot */
-struct SnapShotRecord {
-	unsigned int firstBackingPage;
-};
-
-/** @brief Backing store page */
-typedef unsigned char snapshot_page_t[PAGESIZE];
 
-/* List the base address of the corresponding page in the backing store so we
- * know where to copy it to */
-struct BackingPageRecord {
-	void *basePtrOfPage;
-};
+#define SHARED_MEMORY_DEFAULT  (200 * ((size_t)1 << 20))	// 100mb for the shared memory
+#define STACK_SIZE_DEFAULT      (((size_t)1 << 20) * 20)	// 20 mb out of the above 100 mb for my stack
 
-/* Struct for each memory region */
-struct MemoryRegion {
-	void *basePtr; // base of memory region
-	int sizeInPages; // size of memory region in pages
-};
+struct fork_snapshotter {
+	/** @brief Pointer to the shared (non-snapshot) memory heap base
+	 * (NOTE: this has size SHARED_MEMORY_DEFAULT - sizeof(*fork_snap)) */
+	void *mSharedMemoryBase;
 
-/** ReturnPageAlignedAddress returns a page aligned address for the
- * address being added as a side effect the numBytes are also changed.
- */
-static void * ReturnPageAlignedAddress(void *addr)
-{
-	return (void *)(((uintptr_t)addr) & ~(PAGESIZE - 1));
-}
+	/** @brief Pointer to the shared (non-snapshot) stack region */
+	void *mStackBase;
 
-/* Primary struct for snapshotting system */
-struct mprot_snapshotter {
-	mprot_snapshotter(unsigned int numbackingpages, unsigned int numsnapshots, unsigned int nummemoryregions);
-	~mprot_snapshotter();
+	/** @brief Size of the shared stack */
+	size_t mStackSize;
 
-	struct MemoryRegion *regionsToSnapShot; //This pointer references an array of memory regions to snapshot
-	snapshot_page_t *backingStore; //This pointer references an array of snapshotpage's that form the backing store
-	void *backingStoreBasePtr; //This pointer references an array of snapshotpage's that form the backing store
-	struct BackingPageRecord *backingRecords; //This pointer references an array of backingpagerecord's (same number of elements as backingstore
-	struct SnapShotRecord *snapShots; //This pointer references the snapshot array
+	/**
+	 * @brief Stores the ID that we are attempting to roll back to
+	 *
+	 * Used in inter-process communication so that each process can
+	 * determine whether or not to take over execution (w/ matching ID) or
+	 * exit (we're rolling back even further). Dubiously marked 'volatile'
+	 * to prevent compiler optimizations from messing with the
+	 * inter-process behavior.
+	 */
+	volatile snapshot_id mIDToRollback;
 
-	unsigned int lastSnapShot; //Stores the next snapshot record we should use
-	unsigned int lastBackingPage; //Stores the next backingpage we should use
-	unsigned int lastRegion; //Stores the next memory region to be used
 
-	unsigned int maxRegions; //Stores the max number of memory regions we support
-	unsigned int maxBackingPages; //Stores the total number of backing pages
-	unsigned int maxSnapShots; //Stores the total number of snapshots we allow
 
-	MEMALLOC
+	/** @brief Inter-process tracking of the next snapshot ID */
+	snapshot_id currSnapShotID;
 };
 
-static struct mprot_snapshotter *mprot_snap = NULL;
-
-mprot_snapshotter::mprot_snapshotter(unsigned int backing_pages, unsigned int snapshots, unsigned int regions) :
-	lastSnapShot(0),
-	lastBackingPage(0),
-	lastRegion(0),
-	maxRegions(regions),
-	maxBackingPages(backing_pages),
-	maxSnapShots(snapshots)
-{
-	regionsToSnapShot = (struct MemoryRegion *)model_malloc(sizeof(struct MemoryRegion) * regions);
-	backingStoreBasePtr = (void *)model_malloc(sizeof(snapshot_page_t) * (backing_pages + 1));
-	//Page align the backingstorepages
-	backingStore = (snapshot_page_t *)PageAlignAddressUpward(backingStoreBasePtr);
-	backingRecords = (struct BackingPageRecord *)model_malloc(sizeof(struct BackingPageRecord) * backing_pages);
-	snapShots = (struct SnapShotRecord *)model_malloc(sizeof(struct SnapShotRecord) * snapshots);
-}
-
-mprot_snapshotter::~mprot_snapshotter()
-{
-	model_free(regionsToSnapShot);
-	model_free(backingStoreBasePtr);
-	model_free(backingRecords);
-	model_free(snapShots);
-}
+static struct fork_snapshotter *fork_snap = NULL;
+ucontext_t shared_ctxt;
 
-/** mprot_handle_pf is the page fault handler for mprotect based snapshotting
- * algorithm.
+/** @statics
+ *   These variables are necessary because the stack is shared region and
+ *   there exists a race between all processes executing the same function.
+ *   To avoid the problem above, we require variables allocated in 'safe' regions.
+ *   The bug was actually observed with the forkID, these variables below are
+ *   used to indicate the various contexts to which to switch to.
+ *
+ *   @private_ctxt: the context which is internal to the current process. Used
+ *   for running the internal snapshot/rollback loop.
+ *   @exit_ctxt: a special context used just for exiting from a process (so we
+ *   can use swapcontext() instead of setcontext() + hacks)
+ *   @snapshotid: it is a running counter for the various forked processes
+ *   snapshotid. it is incremented and set in a persistently shared record
  */
-static void mprot_handle_pf(int sig, siginfo_t *si, void *unused)
-{
-	if (si->si_code == SEGV_MAPERR) {
-		model_print("Real Fault at %p\n", si->si_addr);
-		print_trace();
-		model_print("For debugging, place breakpoint at: %s:%d\n",
-				__FILE__, __LINE__);
-		exit(EXIT_FAILURE);
-	}
-	void* addr = ReturnPageAlignedAddress(si->si_addr);
-
-	unsigned int backingpage = mprot_snap->lastBackingPage++; //Could run out of pages...
-	if (backingpage == mprot_snap->maxBackingPages) {
-		model_print("Out of backing pages at %p\n", si->si_addr);
-		exit(EXIT_FAILURE);
-	}
-
-	//copy page
-	memcpy(&(mprot_snap->backingStore[backingpage]), addr, sizeof(snapshot_page_t));
-	//remember where to copy page back to
-	mprot_snap->backingRecords[backingpage].basePtrOfPage = addr;
-	//set protection to read/write
-	if (mprotect(addr, sizeof(snapshot_page_t), PROT_READ | PROT_WRITE)) {
-		perror("mprotect");
-		// Handle error by quitting?
-	}
-}
-
-static void mprot_snapshot_init(unsigned int numbackingpages,
-		unsigned int numsnapshots, unsigned int nummemoryregions,
-		unsigned int numheappages, VoidFuncPtr entryPoint)
-{
-	/* Setup a stack for our signal handler....  */
-	stack_t ss;
-	ss.ss_sp = PageAlignAddressUpward(model_malloc(SIGSTACKSIZE + PAGESIZE - 1));
-	ss.ss_size = SIGSTACKSIZE;
-	ss.ss_flags = 0;
-	sigaltstack(&ss, NULL);
-
-	struct sigaction sa;
-	sa.sa_flags = SA_SIGINFO | SA_NODEFER | SA_RESTART | SA_ONSTACK;
-	sigemptyset(&sa.sa_mask);
-	sa.sa_sigaction = mprot_handle_pf;
-#ifdef MAC
-	if (sigaction(SIGBUS, &sa, NULL) == -1) {
-		model_print("SIGACTION CANNOT BE INSTALLED\n");
-		exit(EXIT_FAILURE);
-	}
-#endif
-	if (sigaction(SIGSEGV, &sa, NULL) == -1) {
-		model_print("SIGACTION CANNOT BE INSTALLED\n");
-		exit(EXIT_FAILURE);
-	}
-
-	mprot_snap = new mprot_snapshotter(numbackingpages, numsnapshots, nummemoryregions);
-
-	// EVIL HACK: We need to make sure that calls into the mprot_handle_pf method don't cause dynamic links
-	// The problem is that we end up protecting state in the dynamic linker...
-	// Solution is to call our signal handler before we start protecting stuff...
-
-	siginfo_t si;
-	memset(&si, 0, sizeof(si));
-	si.si_addr = ss.ss_sp;
-	mprot_handle_pf(SIGSEGV, &si, NULL);
-	mprot_snap->lastBackingPage--; //remove the fake page we copied
-
-	void *basemySpace = model_malloc((numheappages + 1) * PAGESIZE);
-	void *pagealignedbase = PageAlignAddressUpward(basemySpace);
-	user_snapshot_space = create_mspace_with_base(pagealignedbase, numheappages * PAGESIZE, 1);
-	snapshot_add_memory_region(pagealignedbase, numheappages);
-
-	void *base_model_snapshot_space = model_malloc((numheappages + 1) * PAGESIZE);
-	pagealignedbase = PageAlignAddressUpward(base_model_snapshot_space);
-	model_snapshot_space = create_mspace_with_base(pagealignedbase, numheappages * PAGESIZE, 1);
-	snapshot_add_memory_region(pagealignedbase, numheappages);
-
-	entryPoint();
-}
-
-static void mprot_add_to_snapshot(void *addr, unsigned int numPages)
-{
-	unsigned int memoryregion = mprot_snap->lastRegion++;
-	if (memoryregion == mprot_snap->maxRegions) {
-		model_print("Exceeded supported number of memory regions!\n");
-		exit(EXIT_FAILURE);
-	}
-
-	mprot_snap->regionsToSnapShot[memoryregion].basePtr = addr;
-	mprot_snap->regionsToSnapShot[memoryregion].sizeInPages = numPages;
-}
+static ucontext_t private_ctxt;
+static snapshot_id snapshotid = 0;
 
-static snapshot_id mprot_take_snapshot()
+/**
+ * @brief Create a new context, with a given stack and entry function
+ * @param ctxt The context structure to fill
+ * @param stack The stack to run the new context in
+ * @param stacksize The size of the stack
+ * @param func The entry point function for the context
+ */
+static void create_context(ucontext_t *ctxt, void *stack, size_t stacksize,
+													 void (*func)(void))
 {
-	for (unsigned int region = 0; region < mprot_snap->lastRegion; region++) {
-		if (mprotect(mprot_snap->regionsToSnapShot[region].basePtr, mprot_snap->regionsToSnapShot[region].sizeInPages * sizeof(snapshot_page_t), PROT_READ) == -1) {
-			perror("mprotect");
-			model_print("Failed to mprotect inside of takeSnapShot\n");
-			exit(EXIT_FAILURE);
-		}
-	}
-	unsigned int snapshot = mprot_snap->lastSnapShot++;
-	if (snapshot == mprot_snap->maxSnapShots) {
-		model_print("Out of snapshots\n");
-		exit(EXIT_FAILURE);
-	}
-	mprot_snap->snapShots[snapshot].firstBackingPage = mprot_snap->lastBackingPage;
-
-	return snapshot;
+	getcontext(ctxt);
+	ctxt->uc_stack.ss_sp = stack;
+	ctxt->uc_stack.ss_size = stacksize;
+	ctxt->uc_link = NULL;
+	makecontext(ctxt, func, 0);
 }
 
-static void mprot_roll_back(snapshot_id theID)
+/** @brief An empty function, used for an "empty" context which just exits a
+ *  process */
+static void fork_exit()
 {
-#if USE_MPROTECT_SNAPSHOT == 2
-	if (mprot_snap->lastSnapShot == (theID + 1)) {
-		for (unsigned int page = mprot_snap->snapShots[theID].firstBackingPage; page < mprot_snap->lastBackingPage; page++) {
-			memcpy(mprot_snap->backingRecords[page].basePtrOfPage, &mprot_snap->backingStore[page], sizeof(snapshot_page_t));
-		}
-		return;
-	}
-#endif
-
-	HashTable< void *, bool, uintptr_t, 4, model_malloc, model_calloc, model_free> duplicateMap;
-	for (unsigned int region = 0; region < mprot_snap->lastRegion; region++) {
-		if (mprotect(mprot_snap->regionsToSnapShot[region].basePtr, mprot_snap->regionsToSnapShot[region].sizeInPages * sizeof(snapshot_page_t), PROT_READ | PROT_WRITE) == -1) {
-			perror("mprotect");
-			model_print("Failed to mprotect inside of takeSnapShot\n");
-			exit(EXIT_FAILURE);
-		}
-	}
-	for (unsigned int page = mprot_snap->snapShots[theID].firstBackingPage; page < mprot_snap->lastBackingPage; page++) {
-		if (!duplicateMap.contains(mprot_snap->backingRecords[page].basePtrOfPage)) {
-			duplicateMap.put(mprot_snap->backingRecords[page].basePtrOfPage, true);
-			memcpy(mprot_snap->backingRecords[page].basePtrOfPage, &mprot_snap->backingStore[page], sizeof(snapshot_page_t));
-		}
-	}
-	mprot_snap->lastSnapShot = theID;
-	mprot_snap->lastBackingPage = mprot_snap->snapShots[theID].firstBackingPage;
-	mprot_take_snapshot(); //Make sure current snapshot is still good...All later ones are cleared
+	_Exit(EXIT_SUCCESS);
 }
 
-#else /* !USE_MPROTECT_SNAPSHOT */
-
-#define SHARED_MEMORY_DEFAULT  (100 * ((size_t)1 << 20)) // 100mb for the shared memory
-#define STACK_SIZE_DEFAULT      (((size_t)1 << 20) * 20)  // 20 mb out of the above 100 mb for my stack
-
-struct fork_snapshotter {
-	void *mSharedMemoryBase;
-	void *mStackBase;
-	size_t mStackSize;
-	volatile snapshot_id mIDToRollback;
-	ucontext_t mContextToRollback;
-	snapshot_id currSnapShotID;
-};
-
-static struct fork_snapshotter *fork_snap = NULL;
-
-/** @statics
-*   These variables are necessary because the stack is shared region and
-*   there exists a race between all processes executing the same function.
-*   To avoid the problem above, we require variables allocated in 'safe' regions.
-*   The bug was actually observed with the forkID, these variables below are
-*   used to indicate the various contexts to which to switch to.
-*
-*   @savedSnapshotContext: contains the point to which takesnapshot() call should switch to.
-*   @savedUserSnapshotContext: contains the point to which the process whose snapshotid is equal to the rollbackid should switch to
-*   @snapshotid: it is a running counter for the various forked processes snapshotid. it is incremented and set in a persistently shared record
-*/
-static ucontext_t savedSnapshotContext;
-static ucontext_t savedUserSnapshotContext;
-static snapshot_id snapshotid = 0;
-
 static void createSharedMemory()
 {
 	//step 1. create shared memory.
@@ -285,11 +101,12 @@ static void createSharedMemory()
 
 	//Setup snapshot record at top of free region
 	fork_snap = (struct fork_snapshotter *)memMapBase;
-	fork_snap->mSharedMemoryBase = (void *)((uintptr_t)memMapBase + sizeof(struct fork_snapshotter));
+	fork_snap->mSharedMemoryBase = (void *)((uintptr_t)memMapBase + sizeof(*fork_snap));
 	fork_snap->mStackBase = (void *)((uintptr_t)memMapBase + SHARED_MEMORY_DEFAULT);
 	fork_snap->mStackSize = STACK_SIZE_DEFAULT;
 	fork_snap->mIDToRollback = -1;
 	fork_snap->currSnapShotID = 0;
+	sStaticSpace = create_shared_mspace();
 }
 
 /**
@@ -302,123 +119,85 @@ mspace create_shared_mspace()
 {
 	if (!fork_snap)
 		createSharedMemory();
-	return create_mspace_with_base((void *)(fork_snap->mSharedMemoryBase), SHARED_MEMORY_DEFAULT - sizeof(struct fork_snapshotter), 1);
+	return create_mspace_with_base((void *)(fork_snap->mSharedMemoryBase), SHARED_MEMORY_DEFAULT - sizeof(*fork_snap), 1);
 }
 
-static void fork_snapshot_init(unsigned int numbackingpages,
-		unsigned int numsnapshots, unsigned int nummemoryregions,
-		unsigned int numheappages, VoidFuncPtr entryPoint)
+static void fork_snapshot_init(unsigned int numheappages)
 {
 	if (!fork_snap)
 		createSharedMemory();
 
-	void *base_model_snapshot_space = malloc((numheappages + 1) * PAGESIZE);
-	void *pagealignedbase = PageAlignAddressUpward(base_model_snapshot_space);
-	model_snapshot_space = create_mspace_with_base(pagealignedbase, numheappages * PAGESIZE, 1);
+	model_snapshot_space = create_mspace(numheappages * PAGESIZE, 1);
+}
 
-	//step 2 setup the stack context.
-	ucontext_t newContext;
-	getcontext(&newContext);
-	newContext.uc_stack.ss_sp = fork_snap->mStackBase;
-	newContext.uc_stack.ss_size = STACK_SIZE_DEFAULT;
-	makecontext(&newContext, entryPoint, 0);
-	/* switch to a new entryPoint context, on a new stack */
-	model_swapcontext(&savedSnapshotContext, &newContext);
+volatile int modellock = 0;
 
+static void fork_loop() {
 	/* switch back here when takesnapshot is called */
-	pid_t forkedID = 0;
 	snapshotid = fork_snap->currSnapShotID;
-	/* This bool indicates that the current process's snapshotid is same
-		 as the id to which the rollback needs to occur */
+	if (model->params.nofork) {
+		setcontext(&shared_ctxt);
+		_Exit(EXIT_SUCCESS);
+	}
 
-	bool rollback = false;
 	while (true) {
+		pid_t forkedID;
 		fork_snap->currSnapShotID = snapshotid + 1;
+
+		modellock = 1;
 		forkedID = fork();
+		modellock = 0;
 
 		if (0 == forkedID) {
-			/* If the rollback bool is set, switch to the context we need to
-				 return to during a rollback. */
-			if (rollback) {
-				setcontext(&(fork_snap->mContextToRollback));
-			} else {
-				/*Child process which is forked as a result of takesnapshot
-					call should switch back to the takesnapshot context*/
-				setcontext(&savedUserSnapshotContext);
-			}
+			setcontext(&shared_ctxt);
 		} else {
-			int status;
-			int retVal;
-
-			DEBUG("The process id of child is %d and the process id of this process is %d and snapshot id is %d\n",
-			        forkedID, getpid(), snapshotid);
-
-			do {
-				retVal = waitpid(forkedID, &status, 0);
-			} while (-1 == retVal && errno == EINTR);
-
-			if (fork_snap->mIDToRollback != snapshotid) {
-				exit(EXIT_SUCCESS);
+			DEBUG("parent PID: %d, child PID: %d, snapshot ID: %d\n",
+						getpid(), forkedID, snapshotid);
+
+			while (waitpid(forkedID, NULL, 0) < 0) {
+				/* waitpid() may be interrupted */
+				if (errno != EINTR) {
+					perror("waitpid");
+					exit(EXIT_FAILURE);
+				}
 			}
-			rollback = true;
+
+			if (fork_snap->mIDToRollback != snapshotid)
+				_Exit(EXIT_SUCCESS);
 		}
 	}
 }
 
-static snapshot_id fork_take_snapshot()
-{
-	model_swapcontext(&savedUserSnapshotContext, &savedSnapshotContext);
+static void fork_startExecution() {
+	/* switch to a new entryPoint context, on a new stack */
+	create_context(&private_ctxt, snapshot_calloc(STACK_SIZE_DEFAULT, 1), STACK_SIZE_DEFAULT, fork_loop);
+}
+
+static snapshot_id fork_take_snapshot() {
+	model_swapcontext(&shared_ctxt, &private_ctxt);
 	DEBUG("TAKESNAPSHOT RETURN\n");
+	fork_snap->mIDToRollback = -1;
 	return snapshotid;
 }
 
 static void fork_roll_back(snapshot_id theID)
 {
+	DEBUG("Rollback\n");
 	fork_snap->mIDToRollback = theID;
-	volatile int sTemp = 0;
-	getcontext(&fork_snap->mContextToRollback);
-	/*
-	 * This is used to quit the process on rollback, so that the process
-	 * which needs to rollback can quit allowing the process whose
-	 * snapshotid matches the rollbackid to switch to this context and
-	 * continue....
-	 */
-	if (!sTemp) {
-		sTemp = 1;
-		DEBUG("Invoked rollback\n");
-		exit(EXIT_SUCCESS);
-	}
-	/*
-	 * This fix obviates the need for a finalize call. hence less dependences for model-checker....
-	 */
-	fork_snap->mIDToRollback = -1;
+	fork_exit();
 }
 
-#endif /* !USE_MPROTECT_SNAPSHOT */
-
 /**
  * @brief Initializes the snapshot system
  * @param entryPoint the function that should run the program.
  */
-void snapshot_system_init(unsigned int numbackingpages,
-		unsigned int numsnapshots, unsigned int nummemoryregions,
-		unsigned int numheappages, VoidFuncPtr entryPoint)
+void snapshot_system_init(unsigned int numheappages)
 {
-#if USE_MPROTECT_SNAPSHOT
-	mprot_snapshot_init(numbackingpages, numsnapshots, nummemoryregions, numheappages, entryPoint);
-#else
-	fork_snapshot_init(numbackingpages, numsnapshots, nummemoryregions, numheappages, entryPoint);
-#endif
+	fork_snapshot_init(numheappages);
 }
 
-/** Assumes that addr is page aligned. */
-void snapshot_add_memory_region(void *addr, unsigned int numPages)
-{
-#if USE_MPROTECT_SNAPSHOT
-	mprot_add_to_snapshot(addr, numPages);
-#else
-	/* not needed for fork-based snapshotting */
-#endif
+void startExecution() {
+	fork_startExecution();
 }
 
 /** Takes a snapshot of memory.
@@ -426,11 +205,7 @@ void snapshot_add_memory_region(void *addr, unsigned int numPages)
  */
 snapshot_id take_snapshot()
 {
-#if USE_MPROTECT_SNAPSHOT
-	return mprot_take_snapshot();
-#else
 	return fork_take_snapshot();
-#endif
 }
 
 /** Rolls the memory state back to the given snapshot identifier.
@@ -438,9 +213,5 @@ snapshot_id take_snapshot()
  */
 void snapshot_roll_back(snapshot_id theID)
 {
-#if USE_MPROTECT_SNAPSHOT
-	mprot_roll_back(theID);
-#else
 	fork_roll_back(theID);
-#endif
 }