libgo: update to Go 1.13beta1 release

    
    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/193497

From-SVN: r275473

1 files changed, 75 insertions, 38 deletions

diff --git a/libgo/go/runtime/malloc.go b/libgo/go/runtime/malloc.go
index e1e908b2859..cee5f6bc4de 100644
--- a/libgo/go/runtime/malloc.go
+++ b/libgo/go/runtime/malloc.go
@@ -335,53 +335,81 @@ const (
 var physPageSize uintptr
 
 // physHugePageSize is the size in bytes of the OS's default physical huge
-// page size whose allocation is opaque to the application. It is assumed
-// and verified to be a power of two.
+// page size whose allocation is opaque to the application.
 //
 // If set, this must be set by the OS init code (typically in osinit) before
 // mallocinit. However, setting it at all is optional, and leaving the default
 // value is always safe (though potentially less efficient).
-//
-// Since physHugePageSize is always assumed to be a power of two,
-// physHugePageShift is defined as physHugePageSize == 1 << physHugePageShift.
-// The purpose of physHugePageShift is to avoid doing divisions in
-// performance critical functions.
-var (
-	physHugePageSize  uintptr
-	physHugePageShift uint
-)
+var physHugePageSize uintptr
 
-// OS-defined helpers:
+// OS memory management abstraction layer
 //
-// sysAlloc obtains a large chunk of zeroed memory from the
-// operating system, typically on the order of a hundred kilobytes
-// or a megabyte.
-// NOTE: sysAlloc returns OS-aligned memory, but the heap allocator
-// may use larger alignment, so the caller must be careful to realign the
-// memory obtained by sysAlloc.
+// Regions of the address space managed by the runtime may be in one of four
+// states at any given time:
+// 1) None - Unreserved and unmapped, the default state of any region.
+// 2) Reserved - Owned by the runtime, but accessing it would cause a fault.
+//               Does not count against the process' memory footprint.
+// 3) Prepared - Reserved, intended not to be backed by physical memory (though
+//               an OS may implement this lazily). Can transition efficiently to
+//               Ready. Accessing memory in such a region is undefined (may
+//               fault, may give back unexpected zeroes, etc.).
+// 4) Ready - may be accessed safely.
 //
-// sysUnused notifies the operating system that the contents
-// of the memory region are no longer needed and can be reused
-// for other purposes.
-// sysUsed notifies the operating system that the contents
-// of the memory region are needed again.
+// This set of states is more than is strictly necessary to support all the
+// currently supported platforms. One could get by with just None, Reserved, and
+// Ready. However, the Prepared state gives us flexibility for performance
+// purposes. For example, on POSIX-y operating systems, Reserved is usually a
+// private anonymous mmap'd region with PROT_NONE set, and to transition
+// to Ready would require setting PROT_READ|PROT_WRITE. However the
+// underspecification of Prepared lets us use just MADV_FREE to transition from
+// Ready to Prepared. Thus with the Prepared state we can set the permission
+// bits just once early on, we can efficiently tell the OS that it's free to
+// take pages away from us when we don't strictly need them.
+//
+// For each OS there is a common set of helpers defined that transition
+// memory regions between these states. The helpers are as follows:
+//
+// sysAlloc transitions an OS-chosen region of memory from None to Ready.
+// More specifically, it obtains a large chunk of zeroed memory from the
+// operating system, typically on the order of a hundred kilobytes
+// or a megabyte. This memory is always immediately available for use.
 //
-// sysFree returns it unconditionally; this is only used if
-// an out-of-memory error has been detected midway through
-// an allocation. It is okay if sysFree is a no-op.
+// sysFree transitions a memory region from any state to None. Therefore, it
+// returns memory unconditionally. It is used if an out-of-memory error has been
+// detected midway through an allocation or to carve out an aligned section of
+// the address space. It is okay if sysFree is a no-op only if sysReserve always
+// returns a memory region aligned to the heap allocator's alignment
+// restrictions.
 //
-// sysReserve reserves address space without allocating memory.
+// sysReserve transitions a memory region from None to Reserved. It reserves
+// address space in such a way that it would cause a fatal fault upon access
+// (either via permissions or not committing the memory). Such a reservation is
+// thus never backed by physical memory.
 // If the pointer passed to it is non-nil, the caller wants the
 // reservation there, but sysReserve can still choose another
 // location if that one is unavailable.
 // NOTE: sysReserve returns OS-aligned memory, but the heap allocator
 // may use larger alignment, so the caller must be careful to realign the
-// memory obtained by sysAlloc.
+// memory obtained by sysReserve.
 //
-// sysMap maps previously reserved address space for use.
+// sysMap transitions a memory region from Reserved to Prepared. It ensures the
+// memory region can be efficiently transitioned to Ready.
 //
-// sysFault marks a (already sysAlloc'd) region to fault
-// if accessed. Used only for debugging the runtime.
+// sysUsed transitions a memory region from Prepared to Ready. It notifies the
+// operating system that the memory region is needed and ensures that the region
+// may be safely accessed. This is typically a no-op on systems that don't have
+// an explicit commit step and hard over-commit limits, but is critical on
+// Windows, for example.
+//
+// sysUnused transitions a memory region from Ready to Prepared. It notifies the
+// operating system that the physical pages backing this memory region are no
+// longer needed and can be reused for other purposes. The contents of a
+// sysUnused memory region are considered forfeit and the region must not be
+// accessed again until sysUsed is called.
+//
+// sysFault transitions a memory region from Ready or Prepared to Reserved. It
+// marks a region such that it will always fault if accessed. Used only for
+// debugging the runtime.
 
 func mallocinit() {
 	if class_to_size[_TinySizeClass] != _TinySize {
@@ -422,7 +450,7 @@ func mallocinit() {
 	_g_.m.mcache = allocmcache()
 
 	// Create initial arena growth hints.
-	if sys.PtrSize == 8 && GOARCH != "wasm" {
+	if sys.PtrSize == 8 {
 		// On a 64-bit machine, we pick the following hints
 		// because:
 		//
@@ -559,6 +587,9 @@ func mallocinit() {
 // heapArenaBytes. sysAlloc returns nil on failure.
 // There is no corresponding free function.
 //
+// sysAlloc returns a memory region in the Prepared state. This region must
+// be transitioned to Ready before use.
+//
 // h must be locked.
 func (h *mheap) sysAlloc(n uintptr) (v unsafe.Pointer, size uintptr) {
 	n = round(n, heapArenaBytes)
@@ -600,7 +631,7 @@ func (h *mheap) sysAlloc(n uintptr) (v unsafe.Pointer, size uintptr) {
 		// TODO: This would be cleaner if sysReserve could be
 		// told to only return the requested address. In
 		// particular, this is already how Windows behaves, so
-		// it would simply things there.
+		// it would simplify things there.
 		if v != nil {
 			sysFree(v, n, nil)
 		}
@@ -657,7 +688,7 @@ func (h *mheap) sysAlloc(n uintptr) (v unsafe.Pointer, size uintptr) {
 		throw("misrounded allocation in sysAlloc")
 	}
 
-	// Back the reservation.
+	// Transition from Reserved to Prepared.
 	sysMap(v, size, &memstats.heap_sys)
 
 mapped:
@@ -897,7 +928,7 @@ func mallocgc(size uintptr, typ *_type, needzero bool) unsafe.Pointer {
 	dataSize := size
 	c := gomcache()
 	var x unsafe.Pointer
-	noscan := typ == nil || typ.kind&kindNoPointers != 0
+	noscan := typ == nil || typ.ptrdata == 0
 	if size <= maxSmallSize {
 		if noscan && size < maxTinySize {
 			// Tiny allocator.
@@ -1115,6 +1146,11 @@ func reflect_unsafe_New(typ *_type) unsafe.Pointer {
 	return mallocgc(typ.size, typ, true)
 }
 
+//go:linkname reflectlite_unsafe_New internal..z2freflectlite.unsafe_New
+func reflectlite_unsafe_New(typ *_type) unsafe.Pointer {
+	return mallocgc(typ.size, typ, true)
+}
+
 // newarray allocates an array of n elements of type typ.
 func newarray(typ *_type, n int) unsafe.Pointer {
 	if n == 1 {
@@ -1317,8 +1353,8 @@ func inPersistentAlloc(p uintptr) bool {
 }
 
 // linearAlloc is a simple linear allocator that pre-reserves a region
-// of memory and then maps that region as needed. The caller is
-// responsible for locking.
+// of memory and then maps that region into the Ready state as needed. The
+// caller is responsible for locking.
 type linearAlloc struct {
 	next   uintptr // next free byte
 	mapped uintptr // one byte past end of mapped space
@@ -1337,8 +1373,9 @@ func (l *linearAlloc) alloc(size, align uintptr, sysStat *uint64) unsafe.Pointer
 	}
 	l.next = p + size
 	if pEnd := round(l.next-1, physPageSize); pEnd > l.mapped {
-		// We need to map more of the reserved space.
+		// Transition from Reserved to Prepared to Ready.
 		sysMap(unsafe.Pointer(l.mapped), pEnd-l.mapped, sysStat)
+		sysUsed(unsafe.Pointer(l.mapped), pEnd-l.mapped)
 		l.mapped = pEnd
 	}
 	return unsafe.Pointer(p)