Switch maintanance (#18668)

* Fix and improve Nintendo Switch support

* Document the necessity for nimAllocPagesViaMalloc

* update changelog

* Use --gc:orc in examples

lib/system/osalloc.nim

@@ -103,117 +103,6 @@ elif defined(emscripten) and not defined(StandaloneHeapSize):
 elif defined(genode) and not defined(StandaloneHeapSize):
   include genode/alloc # osAllocPages, osTryAllocPages, osDeallocPages
 
-elif defined(nintendoswitch) and not defined(StandaloneHeapSize):
-
-  import nintendoswitch/switch_memory
-
-  type
-    PSwitchBlock = ptr NSwitchBlock
-    ## This will hold the heap pointer data in a separate
-    ## block of memory that is PageSize bytes above
-    ## the requested memory. It's the only good way
-    ## to pass around data with heap allocations
-    NSwitchBlock {.pure, inheritable.} = object
-      realSize: int
-      heap: pointer           # pointer to main heap alloc
-      heapMirror: pointer     # pointer to virtmem mapped heap
-
-  proc alignSize(size: int): int {.inline.} =
-    ## Align a size integer to be in multiples of PageSize
-    ## The nintendo switch will not allocate memory that is not
-    ## aligned to 0x1000 bytes and will just crash.
-    (size + (PageSize - 1)) and not (PageSize - 1)
-
-  proc deallocate(heapMirror: pointer, heap: pointer, size: int) =
-    # Unmap the allocated memory
-    discard svcUnmapMemory(heapMirror, heap, size.uint64)
-    # These should be called (theoretically), but referencing them crashes the switch.
-    # The above call seems to free all heap memory, so these are not needed.
-    # virtmemFreeMap(nswitchBlock.heapMirror, nswitchBlock.realSize.csize)
-    # free(nswitchBlock.heap)
-
-  proc freeMem(p: pointer) =
-    # Retrieve the switch block data from the pointer we set before
-    # The data is located just sizeof(NSwitchBlock) bytes below
-    # the top of the pointer to the heap
-    let
-      nswitchDescrPos = cast[ByteAddress](p) -% sizeof(NSwitchBlock)
-      nswitchBlock = cast[PSwitchBlock](nswitchDescrPos)
-
-    deallocate(
-      nswitchBlock.heapMirror, nswitchBlock.heap, nswitchBlock.realSize
-    )
-
-  proc storeHeapData(address, heapMirror, heap: pointer, size: int) {.inline.} =
-    ## Store data in the heap for deallocation purposes later
-
-    # the position of our heap pointer data. Since we allocated PageSize extra
-    # bytes, we should have a buffer on top of the requested size of at least
-    # PageSize bytes, which is much larger than sizeof(NSwitchBlock). So we
-    # decrement the address by sizeof(NSwitchBlock) and use that address
-    # to store our pointer data
-    let nswitchBlockPos = cast[ByteAddress](address) -% sizeof(NSwitchBlock)
-
-    # We need to store this in a pointer obj (PSwitchBlock) so that the data sticks
-    # at the address we've chosen. If NSwitchBlock is used here, the data will
-    # be all 0 when we try to retrieve it later.
-    var nswitchBlock = cast[PSwitchBlock](nswitchBlockPos)
-    nswitchBlock.realSize = size
-    nswitchBlock.heap = heap
-    nswitchBlock.heapMirror = heapMirror
-
-  proc getOriginalHeapPosition(address: pointer, difference: int): pointer {.inline.} =
-    ## This function sets the heap back to the originally requested
-    ## size
-    let
-      pos = cast[int](address)
-      newPos = cast[ByteAddress](pos) +% difference
-
-    return cast[pointer](newPos)
-
-  template allocPages(size: int, outOfMemoryStmt: untyped): untyped =
-    # This is to ensure we get a block of memory the requested
-    # size, as well as space to store our structure
-    let realSize = alignSize(size + sizeof(NSwitchBlock))
-
-    let heap = memalign(PageSize, realSize)
-
-    if heap.isNil:
-      outOfMemoryStmt
-
-    let heapMirror = virtmemReserveMap(realSize.csize)
-    result = heapMirror
-
-    let rc = svcMapMemory(heapMirror, heap, realSize.uint64)
-    # Any return code not equal 0 means an error in libnx
-    if rc.uint32 != 0:
-      deallocate(heapMirror, heap, realSize)
-      outOfMemoryStmt
-
-    # set result to be the original size requirement
-    result = getOriginalHeapPosition(result, realSize - size)
-
-    storeHeapData(result, heapMirror, heap, realSize)
-
-  proc osAllocPages(size: int): pointer {.inline.} =
-    allocPages(size):
-      raiseOutOfMem()
-
-  proc osTryAllocPages(size: int): pointer =
-    allocPages(size):
-      return nil
-
-  proc osDeallocPages(p: pointer, size: int) =
-    # Note that in order for the Switch not to crash, a call to
-    # deallocHeap(runFinalizers = true, allowGcAfterwards = false)
-    # must be run before gfxExit(). The Switch requires all memory
-    # to be deallocated before the graphics application has exited.
-    #
-    # gfxExit() can be found in <switch/gfx/gfx.h> in the github
-    # repo https://github.com/switchbrew/libnx
-    when reallyOsDealloc:
-      freeMem(p)
-
 elif defined(posix) and not defined(StandaloneHeapSize):
   const
     PROT_READ  = 1             # page can be read