sortix--sortix/libc/stdlib/heap.cpp

/*******************************************************************************

    Copyright(C) Jonas 'Sortie' Termansen 2011, 2012, 2013.

    This file is part of the Sortix C Library.

    The Sortix C Library is free software: you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License as published by
    the Free Software Foundation, either version 3 of the License, or (at your
    option) any later version.

    The Sortix C Library is distributed in the hope that it will be useful, but
    WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
    or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
    License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with the Sortix C Library. If not, see <http://www.gnu.org/licenses/>.

    stdlib/heap.cpp
    Functions that allocate/free memory from a dynamic memory heap.

*******************************************************************************/

#include <sys/mman.h>

#ifdef SORTIX_KERNEL
#define HEAP_GROWS_DOWNWARDS
#endif

#ifndef SORTIX_KERNEL
#include <error.h>
#include <stdio.h>
#include <unistd.h>
#endif

#include <assert.h>
#include <errno.h>
#include <malloc.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>

#define PARANOIA 1

#ifdef SORTIX_KERNEL
#include <sortix/kernel/decl.h>
#include <sortix/kernel/addralloc.h>
#include <sortix/kernel/kthread.h>
#include <sortix/kernel/log.h>
#include <sortix/kernel/memorymanagement.h>
#include <sortix/kernel/panic.h>
#endif

//
// This first section is just magic compiler/platform stuff, you should
// skip ahead to the actual algorithm.
//

#if defined(__x86_64__)
const size_t MAGIC = 0xDEADDEADDEADDEADUL;
const size_t ALIGNMENT = 16UL;
#else
const size_t MAGIC = 0xDEADDEADUL;
const size_t ALIGNMENT = 8UL;
#endif

const size_t PAGESIZE = 4UL * 1024UL; // 4 KiB
const size_t NUMBINS = 8UL * sizeof(size_t);

static uintptr_t wilderness;

#ifdef SORTIX_KERNEL
static uintptr_t GetHeapStart()
{
	return Sortix::GetHeapUpper();
}

static void FreeMemory(uintptr_t where, size_t bytes)
{
	assert(Sortix::Page::IsAligned(where + bytes));

	while ( bytes )
	{
		addr_t page = Sortix::Memory::Unmap(where);
		Sortix::Page::Put(page);

		bytes -= PAGESIZE;
		where += PAGESIZE;
	}
}

static bool AllocateMemory(uintptr_t where, size_t bytes)
{
	assert(Sortix::Page::IsAligned(where + bytes));

	uintptr_t pos = where;

	while ( bytes )
	{
		addr_t page = Sortix::Page::Get();
		if ( !page )
		{
			FreeMemory(where, pos-where);
			return false;
		}

		if ( !Sortix::Memory::Map(page, pos, PROT_KREAD | PROT_KWRITE) )
		{
			Sortix::Page::Put(page);
			FreeMemory(where, pos-where);
			return false;
		}

		bytes -= PAGESIZE;
		pos += PAGESIZE;
	}

	return true;
}

static bool ExtendHeap(size_t bytesneeded)
{
	size_t got_bytes = Sortix::ExpandHeap(bytesneeded);
	if ( !got_bytes )
		return false;
	assert(bytesneeded <= got_bytes);

	#ifdef HEAP_GROWS_DOWNWARDS
	uintptr_t newwilderness = wilderness - got_bytes;
	#else
	uintptr_t newwilderness = wilderness + got_bytes;
	#endif

	if ( !AllocateMemory(newwilderness, got_bytes) )
	{
		Sortix::ShrinkHeap(got_bytes);
		return false;
	}

	return true;
}
#else
static uintptr_t GetHeapStart()
{
	uintptr_t base = (uintptr_t) sbrk(0);
	uintptr_t unaligned = base % ALIGNMENT;
	if ( unaligned )
	{
		sbrk(ALIGNMENT-unaligned);
	}
	uintptr_t result = (uintptr_t) sbrk(0);
	return result;
}

static bool ExtendHeap(size_t bytesneeded)
{
	void* newheapend = sbrk(bytesneeded);
	return newheapend != (void*) -1UL;
}
#endif

// TODO: BitScanForward and BitScanReverse are x86 instructions, but
// directly using them messes with the optimizer. Once possible, use
// the inline assembly instead of the C-version of the functions.

// Returns the index of the most significant set bit.
inline size_t BSR(size_t Value)
{
#if 1
	assert(Value > 0);
	for ( size_t I = 8*sizeof(size_t); I > 0; I-- )
	{
		if ( Value & ( 1UL << (I-1) ) ) { return I-1; }
	}
	return 0;
#else
	size_t Result;
	asm("bsr %0, %1" : "=r"(Result) : "r"(Value));
	return Result;
#endif
}

// Returns the index of the least significant set bit.
inline size_t BSF(size_t Value)
{
#if 1
	assert(Value > 0);
	for ( size_t I = 0; I < 8*sizeof(size_t); I++ )
	{
		if ( Value & ( 1UL << I ) ) { return I; }
	}
	return 0;
#else
	size_t Result;
	asm("bsf %0, %1" : "=r"(Result) : "r"(Value));
	return Result;
#endif
}

//
// Now for some helper functions and structures.
//

struct Chunk;
struct Trailer;

#ifdef SORTIX_KERNEL
Sortix::kthread_mutex_t heaplock;
#endif

// The location where the heap originally grows from.
uintptr_t heapstart;

// If heap grows down: Location of the first mapped page.
// If heap grows up: Location of the first not-mapped page.
#if 0 /* forward declared abvce */
static uintptr_t wilderness;
#endif

// How many bytes remain in the wilderness.
size_t wildernesssize;

// How many bytes are the heap allow to grow to (including wilderness).
size_t heapmaxsize;

// How many bytes are currently used for chunks in the heap, which
// excludes the wilderness.
size_t heapsize;

// bins[N] contain a linked list of chunks that are at least 2^(N+1)
// bytes, but less than 2^(N+2) bytes. By selecting the proper bin in
// constant time, we can allocate chunks in constant time.
Chunk* bins[NUMBINS];

// Bit N is set if bin[N] contains a chunk.
size_t bincontainschunks;

static bool IsGoodHeapPointer(void* ptr, size_t size)
{
	uintptr_t ptrlower = (uintptr_t) ptr;
	uintptr_t ptrupper = ptrlower + size;
#ifdef HEAP_GROWS_DOWNWARDS
	uintptr_t heaplower = wilderness;
	uintptr_t heapupper = heapstart;
#else
	uintptr_t heaplower = heapstart;
	uintptr_t heapupper = wilderness;
#endif
	return heaplower <= ptrlower && ptrupper <= heapupper;
}

// A preamble to every chunk providing meta-information.
struct Chunk
{
public:
	size_t size; // Includes size of Chunk and Trailer
	union
	{
		size_t magic;
		Chunk* nextunused;
	};

public:
	bool IsUsed() { return magic == MAGIC; }
	Trailer* GetTrailer();
	Chunk* LeftNeighbor();
	Chunk* RightNeighbor();
	bool IsSane();

};

// A trailer to every chunk providing meta-information.
struct Trailer
{
public:
	union
	{
		size_t magic;
		Chunk* prevunused;
	};
	size_t size; // Includes size of Chunk and Trailer

public:
	bool IsUsed() { return magic == MAGIC; }
	Chunk* GetChunk();

};

const size_t OVERHEAD = sizeof(Chunk) + sizeof(Trailer);

// This is how a real chunk actually looks:
//struct RealChunk
//{
//	Chunk header;
//	byte data[...];
//	Trailer footer;
// };

Trailer* Chunk::GetTrailer()
{
	return (Trailer*) (((uintptr_t) this) + size - sizeof(Trailer));
}

Chunk* Chunk::LeftNeighbor()
{
	Trailer* trailer = (Trailer*) (((uintptr_t) this) - sizeof(Trailer));
	return trailer->GetChunk();
}

Chunk* Chunk::RightNeighbor()
{
	return (Chunk*) (((uintptr_t) this) + size);
}

Chunk* Trailer::GetChunk()
{
	return (Chunk*) (((uintptr_t) this) + sizeof(Trailer) - size);
}

bool Chunk::IsSane()
{
	if ( !IsGoodHeapPointer(this, sizeof(*this)) )
		return false;
	if ( !size ) { return false; }
	size_t binindex = BSR(size);
	Trailer* trailer = GetTrailer();
	if ( !IsGoodHeapPointer(trailer, sizeof(*trailer)) )
		return false;
	if ( trailer->size != size ) { return false; }
	if ( IsUsed() )
	{
		if ( bins[binindex] == this ) { return false; }
		if ( magic != MAGIC || trailer->magic != magic ) { return false; }
	}
	if ( !IsUsed() )
	{
		if ( ((uintptr_t) nextunused) & (ALIGNMENT-1UL) ) { return false; }
		if ( ((uintptr_t) trailer->prevunused) & (ALIGNMENT-1UL) ) { return false; }
		if ( nextunused && !IsGoodHeapPointer(nextunused->GetTrailer(),
		                                      sizeof(Trailer)) )
			return false;
		if ( nextunused && nextunused->GetTrailer()->prevunused != this ) { return false; }

		if ( trailer->prevunused )
		{
			if ( !IsGoodHeapPointer(trailer->prevunused,
			                        sizeof(*trailer->prevunused)) )
				return false;
			if ( bins[binindex] == this ) { return false; }
			if ( trailer->prevunused->nextunused != this ) { return false; }
		}
		if ( !trailer->prevunused )
		{
			if ( bins[binindex] != this ) { return false; }
			if ( !(bincontainschunks & (1UL << binindex)) ) { return false; }
		}
	}
	return true;
}

static void InsertChunk(Chunk* chunk)
{
	// Insert the chunk into the right bin.
	size_t binindex = BSR(chunk->size);
	chunk->GetTrailer()->prevunused = NULL;
	chunk->nextunused = bins[binindex];
	if ( chunk->nextunused )
	{
		assert(chunk->nextunused->IsSane());
		chunk->nextunused->GetTrailer()->prevunused = chunk;
	}
	bins[binindex] = chunk;
	bincontainschunks |= (1UL << binindex);
	assert(chunk->IsSane());
}

__attribute__((unused))
static bool ValidateHeap()
{
	bool foundbin[NUMBINS];
	for ( size_t i = 0; i < NUMBINS; i++ ) { foundbin[i] = false; }

	#ifdef HEAP_GROWS_DOWNWARDS
	Chunk* chunk = (Chunk*) (wilderness + wildernesssize);
	while ( (uintptr_t) chunk < heapstart )
	#else
	Chunk* chunk = (Chunk*) heapstart;
	while ( (uintptr_t) chunk < wilderness - wildernesssize )
	#endif
	{
		size_t timesfound = 0;
		for ( size_t i = 0; i < NUMBINS; i++ )
		{
			if ( chunk == bins[i] ) { foundbin[i] = true; timesfound++; }
		}
		if ( 1 < timesfound ) { return false; }

		if ( !chunk->IsSane() ) { return false; }
		chunk = chunk->RightNeighbor();
	}

	for ( size_t i = 0; i < NUMBINS; i++ )
	{
		if ( !bins[i] )
		{
			if ( foundbin[i] ) { return false; }
			continue;
		}
		if ( !foundbin[i] ) { return false; }
		if ( !bins[i]->IsSane() ) { return false; }
	}

	return true;
}

//
// This is where the actual memory allocation algorithm starts.
//

extern "C" void _init_heap()
{
	heapstart = GetHeapStart();
	heapmaxsize = SIZE_MAX;
	heapsize = 0;
	wilderness = heapstart;
	wildernesssize = 0;
	for ( size_t i = 0; i < NUMBINS; i++ ) { bins[i] = NULL; }
	bincontainschunks = 0;
#ifdef SORTIX_KERNEL
	heaplock = Sortix::KTHREAD_MUTEX_INITIALIZER;
#endif
}

// Attempts to expand the wilderness such that it contains at least
// bytesneeded bytes. This is done by mapping new pages onto into the
// virtual address-space.
static bool ExpandWilderness(size_t bytesneeded)
{
	if ( bytesneeded <= wildernesssize ) { return true; }

	bytesneeded -= wildernesssize;

	// Align the increase on page boundaries.
	const size_t PAGEMASK = ~(PAGESIZE - 1UL);
	bytesneeded = ( bytesneeded + PAGESIZE - 1UL ) & PAGEMASK;

	assert(bytesneeded >= PAGESIZE);

	// TODO: Overflow MAY happen here!
	if ( heapmaxsize <= heapsize + wildernesssize + bytesneeded )
		return errno = ENOMEM, true;

	#ifdef HEAP_GROWS_DOWNWARDS
	uintptr_t newwilderness = wilderness - bytesneeded;
	#else
	uintptr_t newwilderness = wilderness + bytesneeded;
	#endif

	// Attempt to map pages so our wilderness grows.
	if ( !ExtendHeap(bytesneeded) )
		return false;

	wildernesssize += bytesneeded;
	wilderness = newwilderness;

	return true;
}

extern "C" void* malloc(size_t size)
{
	#ifdef SORTIX_KERNEL
	Sortix::ScopedLock scopedlock(&heaplock);
	#endif

	#if 2 <= PARANOIA
	assert(ValidateHeap());
	#endif

	// The size field keeps both the allocation and meta information.
	size += OVERHEAD;

	// Round up to nearest alignment.
	size = (size + ALIGNMENT - 1UL) & (~(ALIGNMENT-1UL));

	// Find the index of the smallest usable bin.
	size_t minbinindex = BSR(size-1UL)+1UL;

	// Make a bitmask that filter away all bins that are too small.
	size_t minbinmask = ~((1UL << minbinindex) - 1UL);

	// Figure out which bins are usable for our chunk.
	size_t availablebins = bincontainschunks & minbinmask;

	if ( availablebins )
	{
		// Find the smallest available bin.
		size_t binindex = BSF(availablebins);

		Chunk* chunk = bins[binindex];
		assert(chunk->IsSane());
		bins[binindex] = chunk->nextunused;

		size_t binsize = 1UL << binindex;

		// Mark the bin as empty if we emptied it.
		if ( !bins[binindex] )
		{
			bincontainschunks ^= binsize;
		}
		else
		{
			Trailer* trailer = bins[binindex]->GetTrailer();
			trailer->prevunused = NULL;
		}

		assert(!bins[binindex] || bins[binindex]->IsSane());

		// If we don't use the entire chunk.
		if ( OVERHEAD <= binsize - size )
		{
			size_t left = binsize - size;
			chunk->size -= left;
			chunk->GetTrailer()->size = chunk->size;

			Chunk* leftchunk = chunk->RightNeighbor();
			leftchunk->size = left;
			Trailer* lefttrailer = leftchunk->GetTrailer();
			lefttrailer->size = left;

			InsertChunk(leftchunk);
		}

		chunk->magic = MAGIC;
		chunk->GetTrailer()->magic = MAGIC;

		#if 3 <= PARANOIA
		assert(ValidateHeap());
		#endif

		uintptr_t result = ((uintptr_t) chunk) + sizeof(Chunk);
		return (void*) result;
	}

	// If no bins are available, try to allocate from the wilderness.

	// Check if the wilderness can meet our requirements.
	if ( wildernesssize < size && !ExpandWilderness(size) )
	{
		errno = ENOMEM;
		return NULL;
	}

	// Carve a new chunk out of the wilderness and initialize it.
	#ifdef HEAP_GROWS_DOWNWARDS
	Chunk* chunk = (Chunk*) (wilderness + wildernesssize - size);
	#else
	Chunk* chunk = (Chunk*) (wilderness - wildernesssize);
	#endif
	assert(size <= wildernesssize);
	wildernesssize -= size;
	heapsize += size;
	assert(IsGoodHeapPointer(chunk, sizeof(*chunk)));
	chunk->size = size;
	Trailer* trailer = chunk->GetTrailer();
	assert(IsGoodHeapPointer(trailer, sizeof(*trailer)));
	trailer->size = size;
	chunk->magic = MAGIC;
	trailer->magic = MAGIC;

	#if 3 <= PARANOIA
	assert(ValidateHeap());
	#endif

	uintptr_t result = ((uintptr_t) chunk) + sizeof(Chunk);
	return (void*) result;
}

static bool IsLeftmostChunk(Chunk* chunk)
{
	#ifdef HEAP_GROWS_DOWNWARDS
	return (uintptr_t) chunk <= wilderness + wildernesssize;
	#else
	return heapstart <= (uintptr_t) chunk;
	#endif
}

static bool IsRightmostChunk(Chunk* chunk)
{
	#ifdef HEAP_GROWS_DOWNWARDS
	return heapstart <= (uintptr_t) chunk + chunk->size;
	#else
	return heapstart + heapsize <= (uintptr_t) chunk + chunk->size;
	#endif
}

// Removes a chunk from its bin.
static void UnlinkChunk(Chunk* chunk)
{
	assert(chunk->IsSane());
	Trailer* trailer = chunk->GetTrailer();
	if ( trailer->prevunused )
	{
		assert(trailer->prevunused->IsSane());
		trailer->prevunused->nextunused = chunk->nextunused;
		if ( chunk->nextunused )
		{
			assert(chunk->nextunused->IsSane());
			chunk->nextunused->GetTrailer()->prevunused = trailer->prevunused;
		}
	}
	else
	{
		if ( chunk->nextunused )
		{
			assert(chunk->nextunused->IsSane());
			chunk->nextunused->GetTrailer()->prevunused = NULL;
		}
		size_t binindex = BSR(chunk->size);
		assert(bins[binindex] == chunk);
		bins[binindex] = chunk->nextunused;
		if ( !bins[binindex] ) { bincontainschunks ^= 1UL << binindex; }
		else { assert(bins[binindex]->IsSane()); }
	}
}

// Transforms a chunk and its neighbors into a single chunk if possible.
static void UnifyNeighbors(Chunk** chunk)
{
	if ( !IsLeftmostChunk(*chunk) )
	{
		Chunk* neighbor = (*chunk)->LeftNeighbor();
		if ( !neighbor->IsUsed() )
		{
			size_t size = neighbor->size;
			size_t chunksize = (*chunk)->size;
			UnlinkChunk(neighbor);
			*chunk = neighbor;
			(*chunk)->size = size + chunksize;
			(*chunk)->GetTrailer()->size = (*chunk)->size;
		}
	}

	if ( !IsRightmostChunk(*chunk) )
	{
		Chunk* neighbor = (*chunk)->RightNeighbor();
		if ( !neighbor->IsUsed() )
		{
			UnlinkChunk(neighbor);
			(*chunk)->size += neighbor->size;
			(*chunk)->GetTrailer()->size = (*chunk)->size;
		}
	}
}

extern "C" void free(void* addr)
{
	#ifdef SORTIX_KERNEL
	Sortix::ScopedLock scopedlock(&heaplock);
	#endif

	#if 2 <= PARANOIA
	assert(ValidateHeap());
	#endif

	if ( !addr) { return; }
	Chunk* chunk = (Chunk*) ((uintptr_t) addr - sizeof(Chunk));
#ifndef SORTIX_KERNEL
	if ( !IsGoodHeapPointer(addr, 1) ||
	     !IsGoodHeapPointer(chunk, sizeof(*chunk)) )
	{
		error(0, 0, "attempted to free(3) non-heap pointer: 0x%zx", addr);
		abort();
	}
	if ( !chunk->IsUsed() )
	{
		error(0, 0, "attempted to free(3) area that doesn't appear to be "
		      "allocated: 0x%zx + 0x%zx", addr);
		abort();
	}
#endif
	assert(chunk->IsUsed());
	assert(chunk->IsSane());

	UnifyNeighbors(&chunk);

	#ifdef HEAP_GROWS_DOWNWARDS
	bool nexttowilderness = IsLeftmostChunk(chunk);
	#else
	bool nexttowilderness = IsRightmostChunk(chunk);
	#endif

	// If possible, let the wilderness regain the memory.
	if ( nexttowilderness )
	{
		heapsize -= chunk->size;
		wildernesssize += chunk->size;
		return;
	}

	InsertChunk(chunk);

	#if 3 <= PARANOIA
	assert(ValidateHeap());
	#endif
}

// TODO: Implement this function properly.
extern "C" void* realloc(void* ptr, size_t size)
{
	if ( !ptr ) { return malloc(size); }
	Chunk* chunk = (Chunk*) ((uintptr_t) ptr - sizeof(Chunk));
	assert(chunk->IsUsed());
	assert(chunk->IsSane());
	size_t allocsize = chunk->size - OVERHEAD;
	if ( size < allocsize ) { return ptr; }
	void* newptr = malloc(size);
	if ( !newptr ) { return NULL; }
	memcpy(newptr, ptr, allocsize);
	free(ptr);
	return newptr;
}