mmap() and newBufferWithBytesNoCopy causing IOAF code -536870211 error if the file is too small - objective-c

Question

I noticed that, while generating a texture from an MTLBuffer created from mmap() via newBufferWithBytesNoCopy, if the size requested by the len argument to mmap, page aligned, is larger than the actual size of the file, page aligned, the mmap call succeeds, and the newBufferWithBytesNoCopy message does not result in a nil return or error, but when I pass the buffer to the GPU to copy the data to an MTLTexture, the following is printed to the console, and all GPU commands fail to perform any action:
Execution of the command buffer was aborted due to an error during execution. Internal Error (IOAF code -536870211)
Here is code to demonstrate the problem:
static id<MTLDevice> Device;
static id<MTLCommandQueue> Queue;
static id<MTLTexture> BlockTexture[3];
#define TEX_LEN_1 1 // These are all made 1 in this question for simplicity
#define TEX_LEN_2 1
#define TEX_LEN_4 1
#define TEX_SIZE ((TEX_LEN_1<<10)+(TEX_LEN_2<<11)+(TEX_LEN_4<<12))
#define PAGE_ALIGN(S) ((S)+PAGE_SIZE-1&~(PAGE_SIZE-1))
int main(void) {
if (!(Queue = [Device = MTLCreateSystemDefaultDevice() newCommandQueue]))
return EXIT_FAILURE;
#autoreleasepool {
const id<MTLBuffer> data = ({
void *const map = ({
NSFileHandle *const file = [NSFileHandle fileHandleForReadingAtPath:[NSBundle.mainBundle pathForResource:#"Content" ofType:nil]];
if (!file)
return EXIT_FAILURE;
mmap(NULL, TEX_SIZE, PROT_READ, MAP_SHARED, file.fileDescriptor, 0);
});
if (map == MAP_FAILED)
return errno;
[Device newBufferWithBytesNoCopy:map length:PAGE_ALIGN(TEX_SIZE) options:MTLResourceStorageModeShared deallocator:^(void *const ptr, const NSUInteger len){
munmap(ptr, len);
}];
});
if (!data)
return EXIT_FAILURE;
const id<MTLCommandBuffer> buffer = [Queue commandBuffer];
const id<MTLBlitCommandEncoder> encoder = [buffer blitCommandEncoder];
if (!encoder)
return EXIT_FAILURE;
{
MTLTextureDescriptor *const descriptor = [MTLTextureDescriptor new];
descriptor.width = descriptor.height = 32;
descriptor.mipmapLevelCount = 6;
descriptor.textureType = MTLTextureType2DArray;
descriptor.storageMode = MTLStorageModePrivate;
const enum MTLPixelFormat format[] = {MTLPixelFormatR8Unorm, MTLPixelFormatRG8Unorm, MTLPixelFormatRGBA8Unorm};
const NSUInteger len[] = {TEX_LEN_1, TEX_LEN_2, TEX_LEN_4};
for (NSUInteger i = 3, off = 0; i--;) {
descriptor.pixelFormat = format[i];
const NSUInteger l = descriptor.arrayLength = len[i];
const id<MTLTexture> texture = [Device newTextureWithDescriptor:descriptor];
if (!texture)
return EXIT_FAILURE;
const NSUInteger br = 32<<i, bi = 1024<<i;
for (NSUInteger j = 0; j < l; off += bi)
[encoder copyFromBuffer:data sourceOffset:off sourceBytesPerRow:br sourceBytesPerImage:bi sourceSize:(const MTLSize){32, 32, 1} toTexture:texture destinationSlice:j++ destinationLevel:0 destinationOrigin:(const MTLOrigin){0}];
[encoder generateMipmapsForTexture:BlockTexture[i] = texture];
}
}
[encoder endEncoding];
[buffer commit];
}
// Rest of code to initialize application (omitted)
}
In this case, the command will fail if the size of the actual Content file is less than 4097 bytes, assuming a 4096 page size. What is the most strange is that neither the mmap() nor the newBufferWithBytesNoCopy fails in this case, but the GPU execution fails so badly that any/all subsequent GPU calls also fail.
Is there a way to cause predictable behavior? I thought that mmap() space beyond the file was just valid 0 memory. Why is this apparently not the case if the space is being used by the GPU? At the very least, how can I detect GPU execution errors or invalid buffers like this to handle them gracefully, besides manually checking if the file is too small? Am I using these functions incorrectly somehow? Is something here undefined behavior?
My research efforts including Google searching for terms such as newBufferWithBytesNoCopy and/or mmap together with 536870211, and got absolutely no results. Now, this question is the only result for such searches.
My guess is this problem has to do with the inner workings of the GPU and/or the MTLBuffer implementation and/or mmap() and its underlying facilities. Not having access to these inner workings, I have no idea how to even start figuring out a solution. I would appreciate an expert to enlighten me as to what is actually going on behind the scenes causing this error, and how to avoid it (besides manually checking if the file is too big, as this is a 'workaround' but does not really fix the problem at its base, or at the very least how to gracefully detect GPU crashes of this type and abort the application gracefully.