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https://github.com/RGBCube/serenity
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3c74dc9f4d
This patch adds two macros to declare per-type allocators: - JS_DECLARE_ALLOCATOR(TypeName) - JS_DEFINE_ALLOCATOR(TypeName) When used, they add a type-specific CellAllocator that the Heap will delegate allocation requests to. The result of this is that GC objects of the same type always end up within the same HeapBlock, drastically reducing the ability to perform type confusion attacks. It also improves HeapBlock utilization, since each block now has cells sized exactly to the type used within that block. (Previously we only had a handful of block sizes available, and most GC allocations ended up with a large amount of slack in their tails.) There is a small performance hit from this, but I'm sure we can make up for it elsewhere. Note that the old size-based allocators still exist, and we fall back to them for any type that doesn't have its own CellAllocator.
64 lines
1.5 KiB
C++
64 lines
1.5 KiB
C++
/*
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* Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <AK/IntrusiveList.h>
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#include <AK/NonnullOwnPtr.h>
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#include <LibJS/Forward.h>
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#include <LibJS/Heap/HeapBlock.h>
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#define JS_DECLARE_ALLOCATOR(ClassName) \
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static JS::TypeIsolatingCellAllocator<ClassName> cell_allocator;
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#define JS_DEFINE_ALLOCATOR(ClassName) \
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JS::TypeIsolatingCellAllocator<ClassName> ClassName::cell_allocator;
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namespace JS {
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class CellAllocator {
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public:
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explicit CellAllocator(size_t cell_size);
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~CellAllocator() = default;
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size_t cell_size() const { return m_cell_size; }
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Cell* allocate_cell(Heap&);
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template<typename Callback>
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IterationDecision for_each_block(Callback callback)
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{
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for (auto& block : m_full_blocks) {
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if (callback(block) == IterationDecision::Break)
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return IterationDecision::Break;
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}
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for (auto& block : m_usable_blocks) {
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if (callback(block) == IterationDecision::Break)
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return IterationDecision::Break;
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}
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return IterationDecision::Continue;
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}
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void block_did_become_empty(Badge<Heap>, HeapBlock&);
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void block_did_become_usable(Badge<Heap>, HeapBlock&);
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private:
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size_t const m_cell_size;
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using BlockList = IntrusiveList<&HeapBlock::m_list_node>;
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BlockList m_full_blocks;
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BlockList m_usable_blocks;
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};
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template<typename T>
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class TypeIsolatingCellAllocator {
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public:
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using CellType = T;
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CellAllocator allocator { sizeof(T) };
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};
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}
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