// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Memory allocator.
//
// This was originally based on tcmalloc, but has diverged quite a bit.
// http://goog-perftools.sourceforge.net/doc/tcmalloc.html

// The main allocator works in runs of pages.
// Small allocation sizes (up to and including 32 kB) are
// rounded to one of about 70 size classes, each of which
// has its own free set of objects of exactly that size.
// Any free page of memory can be split into a set of objects
// of one size class, which are then managed using a free bitmap.
//
// The allocator's data structures are:
//
//	fixalloc: a free-list allocator for fixed-size off-heap objects,
//		used to manage storage used by the allocator.
//	mheap: the malloc heap, managed at page (8192-byte) granularity.
//	mspan: a run of in-use pages managed by the mheap.
//	mcentral: collects all spans of a given size class.
//	mcache: a per-P cache of mspans with free space.
//	mstats: allocation statistics.
//
// Allocating a small object proceeds up a hierarchy of caches:
//
//	1. Round the size up to one of the small size classes
//	   and look in the corresponding mspan in this P's mcache.
//	   Scan the mspan's free bitmap to find a free slot.
//	   If there is a free slot, allocate it.
//	   This can all be done without acquiring a lock.
//
//	2. If the mspan has no free slots, obtain a new mspan
//	   from the mcentral's list of mspans of the required size
//	   class that have free space.
//	   Obtaining a whole span amortizes the cost of locking
//	   the mcentral.
//
//	3. If the mcentral's mspan list is empty, obtain a run
//	   of pages from the mheap to use for the mspan.
//
//	4. If the mheap is empty or has no page runs large enough,
//	   allocate a new group of pages (at least 1MB) from the
//	   operating system. Allocating a large run of pages
//	   amortizes the cost of talking to the operating system.
//
// Sweeping an mspan and freeing objects on it proceeds up a similar
// hierarchy:
//
//	1. If the mspan is being swept in response to allocation, it
//	   is returned to the mcache to satisfy the allocation.
//
//	2. Otherwise, if the mspan still has allocated objects in it,
//	   it is placed on the mcentral free list for the mspan's size
//	   class.
//
//	3. Otherwise, if all objects in the mspan are free, the mspan's
//	   pages are returned to the mheap and the mspan is now dead.
//
// Allocating and freeing a large object uses the mheap
// directly, bypassing the mcache and mcentral.
//
// If mspan.needzero is false, then free object slots in the mspan are
// already zeroed. Otherwise if needzero is true, objects are zeroed as
// they are allocated. There are various benefits to delaying zeroing
// this way:
//
//	1. Stack frame allocation can avoid zeroing altogether.
//
//	2. It exhibits better temporal locality, since the program is
//	   probably about to write to the memory.
//
//	3. We don't zero pages that never get reused.

// Virtual memory layout
//
// The heap consists of a set of arenas, which are 64MB on 64-bit and
// 4MB on 32-bit (heapArenaBytes). Each arena's start address is also
// aligned to the arena size.
//
// Each arena has an associated heapArena object that stores the
// metadata for that arena: the heap bitmap for all words in the arena
// and the span map for all pages in the arena. heapArena objects are
// themselves allocated off-heap.
//
// Since arenas are aligned, the address space can be viewed as a
// series of arena frames. The arena map (mheap_.arenas) maps from
// arena frame number to *heapArena, or nil for parts of the address
// space not backed by the Go heap. The arena map is structured as a
// two-level array consisting of a "L1" arena map and many "L2" arena
// maps; however, since arenas are large, on many architectures, the
// arena map consists of a single, large L2 map.
//
// The arena map covers the entire possible address space, allowing
// the Go heap to use any part of the address space. The allocator
// attempts to keep arenas contiguous so that large spans (and hence
// large objects) can cross arenas.

package runtime

import (
	
	
	
	
)

const (
	debugMalloc = false

	maxTinySize   = _TinySize
	tinySizeClass = _TinySizeClass
	maxSmallSize  = _MaxSmallSize

	pageShift = _PageShift
	pageSize  = _PageSize
	pageMask  = _PageMask
	// By construction, single page spans of the smallest object class
	// have the most objects per span.
	maxObjsPerSpan = pageSize / 8

	concurrentSweep = _ConcurrentSweep

	_PageSize = 1 << _PageShift
	_PageMask = _PageSize - 1

	// _64bit = 1 on 64-bit systems, 0 on 32-bit systems
	_64bit = 1 << (^uintptr(0) >> 63) / 2

	// Tiny allocator parameters, see "Tiny allocator" comment in malloc.go.
	_TinySize      = 16
	_TinySizeClass = int8(2)

	_FixAllocChunk = 16 << 10 // Chunk size for FixAlloc

	// Per-P, per order stack segment cache size.
	_StackCacheSize = 32 * 1024

	// Number of orders that get caching. Order 0 is FixedStack
	// and each successive order is twice as large.
	// We want to cache 2KB, 4KB, 8KB, and 16KB stacks. Larger stacks
	// will be allocated directly.
	// Since FixedStack is different on different systems, we
	// must vary NumStackOrders to keep the same maximum cached size.
	//   OS               | FixedStack | NumStackOrders
	//   -----------------+------------+---------------
	//   linux/darwin/bsd | 2KB        | 4
	//   windows/32       | 4KB        | 3
	//   windows/64       | 8KB        | 2
	//   plan9            | 4KB        | 3
	_NumStackOrders = 4 - sys.PtrSize/4*sys.GoosWindows - 1*sys.GoosPlan9

	// heapAddrBits is the number of bits in a heap address. On
	// amd64, addresses are sign-extended beyond heapAddrBits. On
	// other arches, they are zero-extended.
	//
	// On most 64-bit platforms, we limit this to 48 bits based on a
	// combination of hardware and OS limitations.
	//
	// amd64 hardware limits addresses to 48 bits, sign-extended
	// to 64 bits. Addresses where the top 16 bits are not either
	// all 0 or all 1 are "non-canonical" and invalid. Because of
	// these "negative" addresses, we offset addresses by 1<<47
	// (arenaBaseOffset) on amd64 before computing indexes into
	// the heap arenas index. In 2017, amd64 hardware added
	// support for 57 bit addresses; however, currently only Linux
	// supports this extension and the kernel will never choose an
	// address above 1<<47 unless mmap is called with a hint
	// address above 1<<47 (which we never do).
	//
	// arm64 hardware (as of ARMv8) limits user addresses to 48
	// bits, in the range [0, 1<<48).
	//
	// ppc64, mips64, and s390x support arbitrary 64 bit addresses
	// in hardware. On Linux, Go leans on stricter OS limits. Based
	// on Linux's processor.h, the user address space is limited as
	// follows on 64-bit architectures:
	//
	// Architecture  Name              Maximum Value (exclusive)
	// ---------------------------------------------------------------------
	// amd64         TASK_SIZE_MAX     0x007ffffffff000 (47 bit addresses)
	// arm64         TASK_SIZE_64      0x01000000000000 (48 bit addresses)
	// ppc64{,le}    TASK_SIZE_USER64  0x00400000000000 (46 bit addresses)
	// mips64{,le}   TASK_SIZE64       0x00010000000000 (40 bit addresses)
	// s390x         TASK_SIZE         1<<64 (64 bit addresses)
	//
	// These limits may increase over time, but are currently at
	// most 48 bits except on s390x. On all architectures, Linux
	// starts placing mmap'd regions at addresses that are
	// significantly below 48 bits, so even if it's possible to
	// exceed Go's 48 bit limit, it's extremely unlikely in
	// practice.
	//
	// On 32-bit platforms, we accept the full 32-bit address
	// space because doing so is cheap.
	// mips32 only has access to the low 2GB of virtual memory, so
	// we further limit it to 31 bits.
	//
	// On ios/arm64, although 64-bit pointers are presumably
	// available, pointers are truncated to 33 bits. Furthermore,
	// only the top 4 GiB of the address space are actually available
	// to the application, but we allow the whole 33 bits anyway for
	// simplicity.
	// TODO(mknyszek): Consider limiting it to 32 bits and using
	// arenaBaseOffset to offset into the top 4 GiB.
	//
	// WebAssembly currently has a limit of 4GB linear memory.
	heapAddrBits = (_64bit*(1-sys.GoarchWasm)*(1-sys.GoosIos*sys.GoarchArm64))*48 + (1-_64bit+sys.GoarchWasm)*(32-(sys.GoarchMips+sys.GoarchMipsle)) + 33*sys.GoosIos*sys.GoarchArm64

	// maxAlloc is the maximum size of an allocation. On 64-bit,
	// it's theoretically possible to allocate 1<<heapAddrBits bytes. On
	// 32-bit, however, this is one less than 1<<32 because the
	// number of bytes in the address space doesn't actually fit
	// in a uintptr.
	maxAlloc = (1 << heapAddrBits) - (1-_64bit)*1

	// The number of bits in a heap address, the size of heap
	// arenas, and the L1 and L2 arena map sizes are related by
	//
	//   (1 << addr bits) = arena size * L1 entries * L2 entries
	//
	// Currently, we balance these as follows:
	//
	//       Platform  Addr bits  Arena size  L1 entries   L2 entries
	// --------------  ---------  ----------  ----------  -----------
	//       */64-bit         48        64MB           1    4M (32MB)
	// windows/64-bit         48         4MB          64    1M  (8MB)
	//       */32-bit         32         4MB           1  1024  (4KB)
	//     */mips(le)         31         4MB           1   512  (2KB)

	// heapArenaBytes is the size of a heap arena. The heap
	// consists of mappings of size heapArenaBytes, aligned to
	// heapArenaBytes. The initial heap mapping is one arena.
	//
	// This is currently 64MB on 64-bit non-Windows and 4MB on
	// 32-bit and on Windows. We use smaller arenas on Windows
	// because all committed memory is charged to the process,
	// even if it's not touched. Hence, for processes with small
	// heaps, the mapped arena space needs to be commensurate.
	// This is particularly important with the race detector,
	// since it significantly amplifies the cost of committed
	// memory.
	heapArenaBytes = 1 << logHeapArenaBytes

	// logHeapArenaBytes is log_2 of heapArenaBytes. For clarity,
	// prefer using heapArenaBytes where possible (we need the
	// constant to compute some other constants).
	logHeapArenaBytes = (6+20)*(_64bit*(1-sys.GoosWindows)*(1-sys.GoarchWasm)) + (2+20)*(_64bit*sys.GoosWindows) + (2+20)*(1-_64bit) + (2+20)*sys.GoarchWasm

	// heapArenaBitmapBytes is the size of each heap arena's bitmap.
	heapArenaBitmapBytes = heapArenaBytes / (sys.PtrSize * 8 / 2)

	pagesPerArena = heapArenaBytes / pageSize

	// arenaL1Bits is the number of bits of the arena number
	// covered by the first level arena map.
	//
	// This number should be small, since the first level arena
	// map requires PtrSize*(1<<arenaL1Bits) of space in the
	// binary's BSS. It can be zero, in which case the first level
	// index is effectively unused. There is a performance benefit
	// to this, since the generated code can be more efficient,
	// but comes at the cost of having a large L2 mapping.
	//
	// We use the L1 map on 64-bit Windows because the arena size
	// is small, but the address space is still 48 bits, and
	// there's a high cost to having a large L2.
	arenaL1Bits = 6 * (_64bit * sys.GoosWindows)

	// arenaL2Bits is the number of bits of the arena number
	// covered by the second level arena index.
	//
	// The size of each arena map allocation is proportional to
	// 1<<arenaL2Bits, so it's important that this not be too
	// large. 48 bits leads to 32MB arena index allocations, which
	// is about the practical threshold.
	arenaL2Bits = heapAddrBits - logHeapArenaBytes - arenaL1Bits

	// arenaL1Shift is the number of bits to shift an arena frame
	// number by to compute an index into the first level arena map.
	arenaL1Shift = arenaL2Bits

	// arenaBits is the total bits in a combined arena map index.
	// This is split between the index into the L1 arena map and
	// the L2 arena map.
	arenaBits = arenaL1Bits + arenaL2Bits

	// arenaBaseOffset is the pointer value that corresponds to
	// index 0 in the heap arena map.
	//
	// On amd64, the address space is 48 bits, sign extended to 64
	// bits. This offset lets us handle "negative" addresses (or
	// high addresses if viewed as unsigned).
	//
	// On aix/ppc64, this offset allows to keep the heapAddrBits to
	// 48. Otherwize, it would be 60 in order to handle mmap addresses
	// (in range 0x0a00000000000000 - 0x0afffffffffffff). But in this
	// case, the memory reserved in (s *pageAlloc).init for chunks
	// is causing important slowdowns.
	//
	// On other platforms, the user address space is contiguous
	// and starts at 0, so no offset is necessary.
	arenaBaseOffset = 0xffff800000000000*sys.GoarchAmd64 + 0x0a00000000000000*sys.GoosAix
	// A typed version of this constant that will make it into DWARF (for viewcore).
	arenaBaseOffsetUintptr = uintptr(arenaBaseOffset)

	// Max number of threads to run garbage collection.
	// 2, 3, and 4 are all plausible maximums depending
	// on the hardware details of the machine. The garbage
	// collector scales well to 32 cpus.
	_MaxGcproc = 32

	// minLegalPointer is the smallest possible legal pointer.
	// This is the smallest possible architectural page size,
	// since we assume that the first page is never mapped.
	//
	// This should agree with minZeroPage in the compiler.
	minLegalPointer uintptr = 4096
)

// physPageSize is the size in bytes of the OS's physical pages.
// Mapping and unmapping operations must be done at multiples of
// physPageSize.
//
// This must be set by the OS init code (typically in osinit) before
// mallocinit.
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.
//
// 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
)

// OS memory management abstraction layer
//
// 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.
//
// 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 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 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 sysReserve.
//
// sysMap transitions a memory region from Reserved to Prepared. It ensures the
// memory region can be efficiently transitioned to Ready.
//
// 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 {
		throw("bad TinySizeClass")
	}

	testdefersizes()

	if heapArenaBitmapBytes&(heapArenaBitmapBytes-1) != 0 {
		// heapBits expects modular arithmetic on bitmap
		// addresses to work.
		throw("heapArenaBitmapBytes not a power of 2")
	}

	// Copy class sizes out for statistics table.
	for  := range class_to_size {
		memstats.by_size[].size = uint32(class_to_size[])
	}

	// Check physPageSize.
	if physPageSize == 0 {
		// The OS init code failed to fetch the physical page size.
		throw("failed to get system page size")
	}
	if physPageSize > maxPhysPageSize {
		print("system page size (", physPageSize, ") is larger than maximum page size (", maxPhysPageSize, ")\n")
		throw("bad system page size")
	}
	if physPageSize < minPhysPageSize {
		print("system page size (", physPageSize, ") is smaller than minimum page size (", minPhysPageSize, ")\n")
		throw("bad system page size")
	}
	if physPageSize&(physPageSize-1) != 0 {
		print("system page size (", physPageSize, ") must be a power of 2\n")
		throw("bad system page size")
	}
	if physHugePageSize&(physHugePageSize-1) != 0 {
		print("system huge page size (", physHugePageSize, ") must be a power of 2\n")
		throw("bad system huge page size")
	}
	if physHugePageSize > maxPhysHugePageSize {
		// physHugePageSize is greater than the maximum supported huge page size.
		// Don't throw here, like in the other cases, since a system configured
		// in this way isn't wrong, we just don't have the code to support them.
		// Instead, silently set the huge page size to zero.
		physHugePageSize = 0
	}
	if physHugePageSize != 0 {
		// Since physHugePageSize is a power of 2, it suffices to increase
		// physHugePageShift until 1<<physHugePageShift == physHugePageSize.
		for 1<<physHugePageShift != physHugePageSize {
			physHugePageShift++
		}
	}
	if pagesPerArena%pagesPerSpanRoot != 0 {
		print("pagesPerArena (", pagesPerArena, ") is not divisible by pagesPerSpanRoot (", pagesPerSpanRoot, ")\n")
		throw("bad pagesPerSpanRoot")
	}
	if pagesPerArena%pagesPerReclaimerChunk != 0 {
		print("pagesPerArena (", pagesPerArena, ") is not divisible by pagesPerReclaimerChunk (", pagesPerReclaimerChunk, ")\n")
		throw("bad pagesPerReclaimerChunk")
	}

	// Initialize the heap.
	mheap_.init()
	mcache0 = allocmcache()
	lockInit(&gcBitsArenas.lock, lockRankGcBitsArenas)
	lockInit(&proflock, lockRankProf)
	lockInit(&globalAlloc.mutex, lockRankGlobalAlloc)

	// Create initial arena growth hints.
	if sys.PtrSize == 8 {
		// On a 64-bit machine, we pick the following hints
		// because:
		//
		// 1. Starting from the middle of the address space
		// makes it easier to grow out a contiguous range
		// without running in to some other mapping.
		//
		// 2. This makes Go heap addresses more easily
		// recognizable when debugging.
		//
		// 3. Stack scanning in gccgo is still conservative,
		// so it's important that addresses be distinguishable
		// from other data.
		//
		// Starting at 0x00c0 means that the valid memory addresses
		// will begin 0x00c0, 0x00c1, ...
		// In little-endian, that's c0 00, c1 00, ... None of those are valid
		// UTF-8 sequences, and they are otherwise as far away from
		// ff (likely a common byte) as possible. If that fails, we try other 0xXXc0
		// addresses. An earlier attempt to use 0x11f8 caused out of memory errors
		// on OS X during thread allocations.  0x00c0 causes conflicts with
		// AddressSanitizer which reserves all memory up to 0x0100.
		// These choices reduce the odds of a conservative garbage collector
		// not collecting memory because some non-pointer block of memory
		// had a bit pattern that matched a memory address.
		//
		// However, on arm64, we ignore all this advice above and slam the
		// allocation at 0x40 << 32 because when using 4k pages with 3-level
		// translation buffers, the user address space is limited to 39 bits
		// On ios/arm64, the address space is even smaller.
		//
		// On AIX, mmaps starts at 0x0A00000000000000 for 64-bit.
		// processes.
		for  := 0x7f;  >= 0; -- {
			var  uintptr
			switch {
			case raceenabled:
				// The TSAN runtime requires the heap
				// to be in the range [0x00c000000000,
				// 0x00e000000000).
				 = uintptr()<<32 | uintptrMask&(0x00c0<<32)
				if  >= uintptrMask&0x00e000000000 {
					continue
				}
			case GOARCH == "arm64" && GOOS == "ios":
				 = uintptr()<<40 | uintptrMask&(0x0013<<28)
			case GOARCH == "arm64":
				 = uintptr()<<40 | uintptrMask&(0x0040<<32)
			case GOOS == "aix":
				if  == 0 {
					// We don't use addresses directly after 0x0A00000000000000
					// to avoid collisions with others mmaps done by non-go programs.
					continue
				}
				 = uintptr()<<40 | uintptrMask&(0xa0<<52)
			default:
				 = uintptr()<<40 | uintptrMask&(0x00c0<<32)
			}
			 := (*arenaHint)(mheap_.arenaHintAlloc.alloc())
			.addr = 
			.next, mheap_.arenaHints = mheap_.arenaHints, 
		}
	} else {
		// On a 32-bit machine, we're much more concerned
		// about keeping the usable heap contiguous.
		// Hence:
		//
		// 1. We reserve space for all heapArenas up front so
		// they don't get interleaved with the heap. They're
		// ~258MB, so this isn't too bad. (We could reserve a
		// smaller amount of space up front if this is a
		// problem.)
		//
		// 2. We hint the heap to start right above the end of
		// the binary so we have the best chance of keeping it
		// contiguous.
		//
		// 3. We try to stake out a reasonably large initial
		// heap reservation.

		const  = (1 << arenaBits) * unsafe.Sizeof(heapArena{})
		 := uintptr(sysReserve(nil, ))
		if  != 0 {
			mheap_.heapArenaAlloc.init(, )
		}

		// We want to start the arena low, but if we're linked
		// against C code, it's possible global constructors
		// have called malloc and adjusted the process' brk.
		// Query the brk so we can avoid trying to map the
		// region over it (which will cause the kernel to put
		// the region somewhere else, likely at a high
		// address).
		 := sbrk0()

		// If we ask for the end of the data segment but the
		// operating system requires a little more space
		// before we can start allocating, it will give out a
		// slightly higher pointer. Except QEMU, which is
		// buggy, as usual: it won't adjust the pointer
		// upward. So adjust it upward a little bit ourselves:
		// 1/4 MB to get away from the running binary image.
		 := firstmoduledata.end
		if  <  {
			 = 
		}
		if mheap_.heapArenaAlloc.next <=  &&  < mheap_.heapArenaAlloc.end {
			 = mheap_.heapArenaAlloc.end
		}
		 = alignUp(+(256<<10), heapArenaBytes)
		// Because we're worried about fragmentation on
		// 32-bit, we try to make a large initial reservation.
		 := []uintptr{
			512 << 20,
			256 << 20,
			128 << 20,
		}
		for ,  := range  {
			,  := sysReserveAligned(unsafe.Pointer(), , heapArenaBytes)
			if  != nil {
				mheap_.arena.init(uintptr(), )
				 = mheap_.arena.end // For hint below
				break
			}
		}
		 := (*arenaHint)(mheap_.arenaHintAlloc.alloc())
		.addr = 
		.next, mheap_.arenaHints = mheap_.arenaHints, 
	}
}

// sysAlloc allocates heap arena space for at least n bytes. The
// returned pointer is always heapArenaBytes-aligned and backed by
// h.arenas metadata. The returned size is always a multiple of
// 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 ( *mheap) ( uintptr) ( unsafe.Pointer,  uintptr) {
	assertLockHeld(&.lock)

	 = alignUp(, heapArenaBytes)

	// First, try the arena pre-reservation.
	 = .arena.alloc(, heapArenaBytes, &memstats.heap_sys)
	if  != nil {
		 = 
		goto 
	}

	// Try to grow the heap at a hint address.
	for .arenaHints != nil {
		 := .arenaHints
		 := .addr
		if .down {
			 -= 
		}
		if + <  {
			// We can't use this, so don't ask.
			 = nil
		} else if arenaIndex(+-1) >= 1<<arenaBits {
			// Outside addressable heap. Can't use.
			 = nil
		} else {
			 = sysReserve(unsafe.Pointer(), )
		}
		if  == uintptr() {
			// Success. Update the hint.
			if !.down {
				 += 
			}
			.addr = 
			 = 
			break
		}
		// Failed. Discard this hint and try the next.
		//
		// 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 simplify things there.
		if  != nil {
			sysFree(, , nil)
		}
		.arenaHints = .next
		.arenaHintAlloc.free(unsafe.Pointer())
	}

	if  == 0 {
		if raceenabled {
			// The race detector assumes the heap lives in
			// [0x00c000000000, 0x00e000000000), but we
			// just ran out of hints in this region. Give
			// a nice failure.
			throw("too many address space collisions for -race mode")
		}

		// All of the hints failed, so we'll take any
		// (sufficiently aligned) address the kernel will give
		// us.
		,  = sysReserveAligned(nil, , heapArenaBytes)
		if  == nil {
			return nil, 0
		}

		// Create new hints for extending this region.
		 := (*arenaHint)(.arenaHintAlloc.alloc())
		.addr, .down = uintptr(), true
		.next, mheap_.arenaHints = mheap_.arenaHints, 
		 = (*arenaHint)(.arenaHintAlloc.alloc())
		.addr = uintptr() + 
		.next, mheap_.arenaHints = mheap_.arenaHints, 
	}

	// Check for bad pointers or pointers we can't use.
	{
		var  string
		 := uintptr()
		if + <  {
			 = "region exceeds uintptr range"
		} else if arenaIndex() >= 1<<arenaBits {
			 = "base outside usable address space"
		} else if arenaIndex(+-1) >= 1<<arenaBits {
			 = "end outside usable address space"
		}
		if  != "" {
			// This should be impossible on most architectures,
			// but it would be really confusing to debug.
			print("runtime: memory allocated by OS [", hex(), ", ", hex(+), ") not in usable address space: ", , "\n")
			throw("memory reservation exceeds address space limit")
		}
	}

	if uintptr()&(heapArenaBytes-1) != 0 {
		throw("misrounded allocation in sysAlloc")
	}

	// Transition from Reserved to Prepared.
	sysMap(, , &memstats.heap_sys)

:
	// Create arena metadata.
	for  := arenaIndex(uintptr());  <= arenaIndex(uintptr()+-1); ++ {
		 := .arenas[.l1()]
		if  == nil {
			// Allocate an L2 arena map.
			 = (*[1 << arenaL2Bits]*heapArena)(persistentalloc(unsafe.Sizeof(*), sys.PtrSize, nil))
			if  == nil {
				throw("out of memory allocating heap arena map")
			}
			atomic.StorepNoWB(unsafe.Pointer(&.arenas[.l1()]), unsafe.Pointer())
		}

		if [.l2()] != nil {
			throw("arena already initialized")
		}
		var  *heapArena
		 = (*heapArena)(.heapArenaAlloc.alloc(unsafe.Sizeof(*), sys.PtrSize, &memstats.gcMiscSys))
		if  == nil {
			 = (*heapArena)(persistentalloc(unsafe.Sizeof(*), sys.PtrSize, &memstats.gcMiscSys))
			if  == nil {
				throw("out of memory allocating heap arena metadata")
			}
		}

		// Add the arena to the arenas list.
		if len(.allArenas) == cap(.allArenas) {
			 := 2 * uintptr(cap(.allArenas)) * sys.PtrSize
			if  == 0 {
				 = physPageSize
			}
			 := (*notInHeap)(persistentalloc(, sys.PtrSize, &memstats.gcMiscSys))
			if  == nil {
				throw("out of memory allocating allArenas")
			}
			 := .allArenas
			*(*notInHeapSlice)(unsafe.Pointer(&.allArenas)) = notInHeapSlice{, len(.allArenas), int( / sys.PtrSize)}
			copy(.allArenas, )
			// Do not free the old backing array because
			// there may be concurrent readers. Since we
			// double the array each time, this can lead
			// to at most 2x waste.
		}
		.allArenas = .allArenas[:len(.allArenas)+1]
		.allArenas[len(.allArenas)-1] = 

		// Store atomically just in case an object from the
		// new heap arena becomes visible before the heap lock
		// is released (which shouldn't happen, but there's
		// little downside to this).
		atomic.StorepNoWB(unsafe.Pointer(&[.l2()]), unsafe.Pointer())
	}

	// Tell the race detector about the new heap memory.
	if raceenabled {
		racemapshadow(, )
	}

	return
}

// sysReserveAligned is like sysReserve, but the returned pointer is
// aligned to align bytes. It may reserve either n or n+align bytes,
// so it returns the size that was reserved.
func sysReserveAligned( unsafe.Pointer, ,  uintptr) (unsafe.Pointer, uintptr) {
	// Since the alignment is rather large in uses of this
	// function, we're not likely to get it by chance, so we ask
	// for a larger region and remove the parts we don't need.
	 := 0
:
	 := uintptr(sysReserve(, +))
	switch {
	case  == 0:
		return nil, 0
	case &(-1) == 0:
		// We got lucky and got an aligned region, so we can
		// use the whole thing.
		return unsafe.Pointer(),  + 
	case GOOS == "windows":
		// On Windows we can't release pieces of a
		// reservation, so we release the whole thing and
		// re-reserve the aligned sub-region. This may race,
		// so we may have to try again.
		sysFree(unsafe.Pointer(), +, nil)
		 = alignUp(, )
		 := sysReserve(unsafe.Pointer(), )
		if  != uintptr() {
			// Must have raced. Try again.
			sysFree(, , nil)
			if ++;  == 100 {
				throw("failed to allocate aligned heap memory; too many retries")
			}
			goto 
		}
		// Success.
		return , 
	default:
		// Trim off the unaligned parts.
		 := alignUp(, )
		sysFree(unsafe.Pointer(), -, nil)
		 :=  + 
		 := ( +  + ) - 
		if  > 0 {
			sysFree(unsafe.Pointer(), , nil)
		}
		return unsafe.Pointer(), 
	}
}

// base address for all 0-byte allocations
var zerobase uintptr

// nextFreeFast returns the next free object if one is quickly available.
// Otherwise it returns 0.
func nextFreeFast( *mspan) gclinkptr {
	 := sys.Ctz64(.allocCache) // Is there a free object in the allocCache?
	if  < 64 {
		 := .freeindex + uintptr()
		if  < .nelems {
			 :=  + 1
			if %64 == 0 &&  != .nelems {
				return 0
			}
			.allocCache >>= uint( + 1)
			.freeindex = 
			.allocCount++
			return gclinkptr(*.elemsize + .base())
		}
	}
	return 0
}

// nextFree returns the next free object from the cached span if one is available.
// Otherwise it refills the cache with a span with an available object and
// returns that object along with a flag indicating that this was a heavy
// weight allocation. If it is a heavy weight allocation the caller must
// determine whether a new GC cycle needs to be started or if the GC is active
// whether this goroutine needs to assist the GC.
//
// Must run in a non-preemptible context since otherwise the owner of
// c could change.
func ( *mcache) ( spanClass) ( gclinkptr,  *mspan,  bool) {
	 = .alloc[]
	 = false
	 := .nextFreeIndex()
	if  == .nelems {
		// The span is full.
		if uintptr(.allocCount) != .nelems {
			println("runtime: s.allocCount=", .allocCount, "s.nelems=", .nelems)
			throw("s.allocCount != s.nelems && freeIndex == s.nelems")
		}
		.refill()
		 = true
		 = .alloc[]

		 = .nextFreeIndex()
	}

	if  >= .nelems {
		throw("freeIndex is not valid")
	}

	 = gclinkptr(*.elemsize + .base())
	.allocCount++
	if uintptr(.allocCount) > .nelems {
		println("s.allocCount=", .allocCount, "s.nelems=", .nelems)
		throw("s.allocCount > s.nelems")
	}
	return
}

// Allocate an object of size bytes.
// Small objects are allocated from the per-P cache's free lists.
// Large objects (> 32 kB) are allocated straight from the heap.
func mallocgc( uintptr,  *_type,  bool) unsafe.Pointer {
	if gcphase == _GCmarktermination {
		throw("mallocgc called with gcphase == _GCmarktermination")
	}

	if  == 0 {
		return unsafe.Pointer(&zerobase)
	}

	if debug.malloc {
		if debug.sbrk != 0 {
			 := uintptr(16)
			if  != nil {
				// TODO(austin): This should be just
				//   align = uintptr(typ.align)
				// but that's only 4 on 32-bit platforms,
				// even if there's a uint64 field in typ (see #599).
				// This causes 64-bit atomic accesses to panic.
				// Hence, we use stricter alignment that matches
				// the normal allocator better.
				if &7 == 0 {
					 = 8
				} else if &3 == 0 {
					 = 4
				} else if &1 == 0 {
					 = 2
				} else {
					 = 1
				}
			}
			return persistentalloc(, , &memstats.other_sys)
		}

		if inittrace.active && inittrace.id == getg().goid {
			// Init functions are executed sequentially in a single Go routine.
			inittrace.allocs += 1
		}
	}

	// assistG is the G to charge for this allocation, or nil if
	// GC is not currently active.
	var  *g
	if gcBlackenEnabled != 0 {
		// Charge the current user G for this allocation.
		 = getg()
		if .m.curg != nil {
			 = .m.curg
		}
		// Charge the allocation against the G. We'll account
		// for internal fragmentation at the end of mallocgc.
		.gcAssistBytes -= int64()

		if .gcAssistBytes < 0 {
			// This G is in debt. Assist the GC to correct
			// this before allocating. This must happen
			// before disabling preemption.
			gcAssistAlloc()
		}
	}

	// Set mp.mallocing to keep from being preempted by GC.
	 := acquirem()
	if .mallocing != 0 {
		throw("malloc deadlock")
	}
	if .gsignal == getg() {
		throw("malloc during signal")
	}
	.mallocing = 1

	 := false
	 := 
	 := getMCache()
	if  == nil {
		throw("mallocgc called without a P or outside bootstrapping")
	}
	var  *mspan
	var  unsafe.Pointer
	 :=  == nil || .ptrdata == 0
	if  <= maxSmallSize {
		if  &&  < maxTinySize {
			// Tiny allocator.
			//
			// Tiny allocator combines several tiny allocation requests
			// into a single memory block. The resulting memory block
			// is freed when all subobjects are unreachable. The subobjects
			// must be noscan (don't have pointers), this ensures that
			// the amount of potentially wasted memory is bounded.
			//
			// Size of the memory block used for combining (maxTinySize) is tunable.
			// Current setting is 16 bytes, which relates to 2x worst case memory
			// wastage (when all but one subobjects are unreachable).
			// 8 bytes would result in no wastage at all, but provides less
			// opportunities for combining.
			// 32 bytes provides more opportunities for combining,
			// but can lead to 4x worst case wastage.
			// The best case winning is 8x regardless of block size.
			//
			// Objects obtained from tiny allocator must not be freed explicitly.
			// So when an object will be freed explicitly, we ensure that
			// its size >= maxTinySize.
			//
			// SetFinalizer has a special case for objects potentially coming
			// from tiny allocator, it such case it allows to set finalizers
			// for an inner byte of a memory block.
			//
			// The main targets of tiny allocator are small strings and
			// standalone escaping variables. On a json benchmark
			// the allocator reduces number of allocations by ~12% and
			// reduces heap size by ~20%.
			 := .tinyoffset
			// Align tiny pointer for required (conservative) alignment.
			if &7 == 0 {
				 = alignUp(, 8)
			} else if sys.PtrSize == 4 &&  == 12 {
				// Conservatively align 12-byte objects to 8 bytes on 32-bit
				// systems so that objects whose first field is a 64-bit
				// value is aligned to 8 bytes and does not cause a fault on
				// atomic access. See issue 37262.
				// TODO(mknyszek): Remove this workaround if/when issue 36606
				// is resolved.
				 = alignUp(, 8)
			} else if &3 == 0 {
				 = alignUp(, 4)
			} else if &1 == 0 {
				 = alignUp(, 2)
			}
			if + <= maxTinySize && .tiny != 0 {
				// The object fits into existing tiny block.
				 = unsafe.Pointer(.tiny + )
				.tinyoffset =  + 
				.tinyAllocs++
				.mallocing = 0
				releasem()
				return 
			}
			// Allocate a new maxTinySize block.
			 = .alloc[tinySpanClass]
			 := nextFreeFast()
			if  == 0 {
				, ,  = .nextFree(tinySpanClass)
			}
			 = unsafe.Pointer()
			(*[2]uint64)()[0] = 0
			(*[2]uint64)()[1] = 0
			// See if we need to replace the existing tiny block with the new one
			// based on amount of remaining free space.
			if  < .tinyoffset || .tiny == 0 {
				.tiny = uintptr()
				.tinyoffset = 
			}
			 = maxTinySize
		} else {
			var  uint8
			if  <= smallSizeMax-8 {
				 = size_to_class8[divRoundUp(, smallSizeDiv)]
			} else {
				 = size_to_class128[divRoundUp(-smallSizeMax, largeSizeDiv)]
			}
			 = uintptr(class_to_size[])
			 := makeSpanClass(, )
			 = .alloc[]
			 := nextFreeFast()
			if  == 0 {
				, ,  = .nextFree()
			}
			 = unsafe.Pointer()
			if  && .needzero != 0 {
				memclrNoHeapPointers(unsafe.Pointer(), )
			}
		}
	} else {
		 = true
		 = .allocLarge(, , )
		.freeindex = 1
		.allocCount = 1
		 = unsafe.Pointer(.base())
		 = .elemsize
	}

	var  uintptr
	if ! {
		// If allocating a defer+arg block, now that we've picked a malloc size
		// large enough to hold everything, cut the "asked for" size down to
		// just the defer header, so that the GC bitmap will record the arg block
		// as containing nothing at all (as if it were unused space at the end of
		// a malloc block caused by size rounding).
		// The defer arg areas are scanned as part of scanstack.
		if  == deferType {
			 = unsafe.Sizeof(_defer{})
		}
		heapBitsSetType(uintptr(), , , )
		if  > .size {
			// Array allocation. If there are any
			// pointers, GC has to scan to the last
			// element.
			if .ptrdata != 0 {
				 =  - .size + .ptrdata
			}
		} else {
			 = .ptrdata
		}
		.scanAlloc += 
	}

	// Ensure that the stores above that initialize x to
	// type-safe memory and set the heap bits occur before
	// the caller can make x observable to the garbage
	// collector. Otherwise, on weakly ordered machines,
	// the garbage collector could follow a pointer to x,
	// but see uninitialized memory or stale heap bits.
	publicationBarrier()

	// Allocate black during GC.
	// All slots hold nil so no scanning is needed.
	// This may be racing with GC so do it atomically if there can be
	// a race marking the bit.
	if gcphase != _GCoff {
		gcmarknewobject(, uintptr(), , )
	}

	if raceenabled {
		racemalloc(, )
	}

	if msanenabled {
		msanmalloc(, )
	}

	.mallocing = 0
	releasem()

	if debug.malloc {
		if debug.allocfreetrace != 0 {
			tracealloc(, , )
		}

		if inittrace.active && inittrace.id == getg().goid {
			// Init functions are executed sequentially in a single Go routine.
			inittrace.bytes += uint64()
		}
	}

	if  := MemProfileRate;  > 0 {
		if  != 1 &&  < .nextSample {
			.nextSample -= 
		} else {
			 := acquirem()
			profilealloc(, , )
			releasem()
		}
	}

	if  != nil {
		// Account for internal fragmentation in the assist
		// debt now that we know it.
		.gcAssistBytes -= int64( - )
	}

	if  {
		if  := (gcTrigger{kind: gcTriggerHeap}); .test() {
			gcStart()
		}
	}

	return 
}

// implementation of new builtin
// compiler (both frontend and SSA backend) knows the signature
// of this function
func newobject( *_type) unsafe.Pointer {
	return mallocgc(.size, , true)
}

//go:linkname reflect_unsafe_New reflect.unsafe_New
func reflect_unsafe_New( *_type) unsafe.Pointer {
	return mallocgc(.size, , true)
}

//go:linkname reflectlite_unsafe_New internal/reflectlite.unsafe_New
func reflectlite_unsafe_New( *_type) unsafe.Pointer {
	return mallocgc(.size, , true)
}

// newarray allocates an array of n elements of type typ.
func newarray( *_type,  int) unsafe.Pointer {
	if  == 1 {
		return mallocgc(.size, , true)
	}
	,  := math.MulUintptr(.size, uintptr())
	if  ||  > maxAlloc ||  < 0 {
		panic(plainError("runtime: allocation size out of range"))
	}
	return mallocgc(, , true)
}

//go:linkname reflect_unsafe_NewArray reflect.unsafe_NewArray
func reflect_unsafe_NewArray( *_type,  int) unsafe.Pointer {
	return newarray(, )
}

func profilealloc( *m,  unsafe.Pointer,  uintptr) {
	 := getMCache()
	if  == nil {
		throw("profilealloc called without a P or outside bootstrapping")
	}
	.nextSample = nextSample()
	mProf_Malloc(, )
}

// nextSample returns the next sampling point for heap profiling. The goal is
// to sample allocations on average every MemProfileRate bytes, but with a
// completely random distribution over the allocation timeline; this
// corresponds to a Poisson process with parameter MemProfileRate. In Poisson
// processes, the distance between two samples follows the exponential
// distribution (exp(MemProfileRate)), so the best return value is a random
// number taken from an exponential distribution whose mean is MemProfileRate.
func nextSample() uintptr {
	if MemProfileRate == 1 {
		// Callers assign our return value to
		// mcache.next_sample, but next_sample is not used
		// when the rate is 1. So avoid the math below and
		// just return something.
		return 0
	}
	if GOOS == "plan9" {
		// Plan 9 doesn't support floating point in note handler.
		if  := getg();  == .m.gsignal {
			return nextSampleNoFP()
		}
	}

	return uintptr(fastexprand(MemProfileRate))
}

// fastexprand returns a random number from an exponential distribution with
// the specified mean.
func fastexprand( int) int32 {
	// Avoid overflow. Maximum possible step is
	// -ln(1/(1<<randomBitCount)) * mean, approximately 20 * mean.
	switch {
	case  > 0x7000000:
		 = 0x7000000
	case  == 0:
		return 0
	}

	// Take a random sample of the exponential distribution exp(-mean*x).
	// The probability distribution function is mean*exp(-mean*x), so the CDF is
	// p = 1 - exp(-mean*x), so
	// q = 1 - p == exp(-mean*x)
	// log_e(q) = -mean*x
	// -log_e(q)/mean = x
	// x = -log_e(q) * mean
	// x = log_2(q) * (-log_e(2)) * mean    ; Using log_2 for efficiency
	const  = 26
	 := fastrand()%(1<<) + 1
	 := fastlog2(float64()) - 
	if  > 0 {
		 = 0
	}
	const  = -0.6931471805599453 // -ln(2)
	return int32(*(*float64())) + 1
}

// nextSampleNoFP is similar to nextSample, but uses older,
// simpler code to avoid floating point.
func nextSampleNoFP() uintptr {
	// Set first allocation sample size.
	 := MemProfileRate
	if  > 0x3fffffff { // make 2*rate not overflow
		 = 0x3fffffff
	}
	if  != 0 {
		return uintptr(fastrand() % uint32(2*))
	}
	return 0
}

type persistentAlloc struct {
	base *notInHeap
	off  uintptr
}

var globalAlloc struct {
	mutex
	persistentAlloc
}

// persistentChunkSize is the number of bytes we allocate when we grow
// a persistentAlloc.
const persistentChunkSize = 256 << 10

// persistentChunks is a list of all the persistent chunks we have
// allocated. The list is maintained through the first word in the
// persistent chunk. This is updated atomically.
var persistentChunks *notInHeap

// Wrapper around sysAlloc that can allocate small chunks.
// There is no associated free operation.
// Intended for things like function/type/debug-related persistent data.
// If align is 0, uses default align (currently 8).
// The returned memory will be zeroed.
//
// Consider marking persistentalloc'd types go:notinheap.
func persistentalloc(,  uintptr,  *sysMemStat) unsafe.Pointer {
	var  *notInHeap
	systemstack(func() {
		 = persistentalloc1(, , )
	})
	return unsafe.Pointer()
}

// Must run on system stack because stack growth can (re)invoke it.
// See issue 9174.
//go:systemstack
func persistentalloc1(,  uintptr,  *sysMemStat) *notInHeap {
	const (
		 = 64 << 10 // VM reservation granularity is 64K on windows
	)

	if  == 0 {
		throw("persistentalloc: size == 0")
	}
	if  != 0 {
		if &(-1) != 0 {
			throw("persistentalloc: align is not a power of 2")
		}
		if  > _PageSize {
			throw("persistentalloc: align is too large")
		}
	} else {
		 = 8
	}

	if  >=  {
		return (*notInHeap)(sysAlloc(, ))
	}

	 := acquirem()
	var  *persistentAlloc
	if  != nil && .p != 0 {
		 = &.p.ptr().palloc
	} else {
		lock(&globalAlloc.mutex)
		 = &globalAlloc.persistentAlloc
	}
	.off = alignUp(.off, )
	if .off+ > persistentChunkSize || .base == nil {
		.base = (*notInHeap)(sysAlloc(persistentChunkSize, &memstats.other_sys))
		if .base == nil {
			if  == &globalAlloc.persistentAlloc {
				unlock(&globalAlloc.mutex)
			}
			throw("runtime: cannot allocate memory")
		}

		// Add the new chunk to the persistentChunks list.
		for {
			 := uintptr(unsafe.Pointer(persistentChunks))
			*(*uintptr)(unsafe.Pointer(.base)) = 
			if atomic.Casuintptr((*uintptr)(unsafe.Pointer(&persistentChunks)), , uintptr(unsafe.Pointer(.base))) {
				break
			}
		}
		.off = alignUp(sys.PtrSize, )
	}
	 := .base.add(.off)
	.off += 
	releasem()
	if  == &globalAlloc.persistentAlloc {
		unlock(&globalAlloc.mutex)
	}

	if  != &memstats.other_sys {
		.add(int64())
		memstats.other_sys.add(-int64())
	}
	return 
}

// inPersistentAlloc reports whether p points to memory allocated by
// persistentalloc. This must be nosplit because it is called by the
// cgo checker code, which is called by the write barrier code.
//go:nosplit
func inPersistentAlloc( uintptr) bool {
	 := atomic.Loaduintptr((*uintptr)(unsafe.Pointer(&persistentChunks)))
	for  != 0 {
		if  >=  &&  < +persistentChunkSize {
			return true
		}
		 = *(*uintptr)(unsafe.Pointer())
	}
	return false
}

// linearAlloc is a simple linear allocator that pre-reserves a region
// 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
	end    uintptr // end of reserved space
}

func ( *linearAlloc) (,  uintptr) {
	if + <  {
		// Chop off the last byte. The runtime isn't prepared
		// to deal with situations where the bounds could overflow.
		// Leave that memory reserved, though, so we don't map it
		// later.
		 -= 1
	}
	.next, .mapped = , 
	.end =  + 
}

func ( *linearAlloc) (,  uintptr,  *sysMemStat) unsafe.Pointer {
	 := alignUp(.next, )
	if + > .end {
		return nil
	}
	.next =  + 
	if  := alignUp(.next-1, physPageSize);  > .mapped {
		// Transition from Reserved to Prepared to Ready.
		sysMap(unsafe.Pointer(.mapped), -.mapped, )
		sysUsed(unsafe.Pointer(.mapped), -.mapped)
		.mapped = 
	}
	return unsafe.Pointer()
}

// notInHeap is off-heap memory allocated by a lower-level allocator
// like sysAlloc or persistentAlloc.
//
// In general, it's better to use real types marked as go:notinheap,
// but this serves as a generic type for situations where that isn't
// possible (like in the allocators).
//
// TODO: Use this as the return type of sysAlloc, persistentAlloc, etc?
//
//go:notinheap
type notInHeap struct{}

func ( *notInHeap) ( uintptr) *notInHeap {
	return (*notInHeap)(unsafe.Pointer(uintptr(unsafe.Pointer()) + ))
}