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https://github.com/RGBCube/serenity
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bd5abbc454
When scanning for potential heap pointers during conservative GC, we look for any value that is an address somewhere inside a heap cell. However, we were failing to account for the slack at the end of a block (which occurs whenever the block storage size isn't an exact multiple of the cell size.) Pointers inside the trailing slack were misidentified as pointers into "last_cell+1". Instead of skipping over them, we would treat this garbage data as a live cell and try to mark it. I believe this is the test-js crash that has been terrorizing Travis for a while. :^)
97 lines
3.1 KiB
C++
97 lines
3.1 KiB
C++
/*
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* Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* 1. Redistributions of source code must retain the above copyright notice, this
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* list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#pragma once
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#include <AK/Types.h>
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#include <LibJS/Forward.h>
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#include <LibJS/Runtime/Cell.h>
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namespace JS {
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class HeapBlock {
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public:
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static constexpr size_t block_size = 16 * KiB;
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static NonnullOwnPtr<HeapBlock> create_with_cell_size(Heap&, size_t);
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void operator delete(void*);
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size_t cell_size() const { return m_cell_size; }
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size_t cell_count() const { return (block_size - sizeof(HeapBlock)) / m_cell_size; }
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Cell* allocate();
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void deallocate(Cell*);
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template<typename Callback>
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void for_each_cell(Callback callback)
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{
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for (size_t i = 0; i < cell_count(); ++i)
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callback(cell(i));
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}
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Heap& heap() { return m_heap; }
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static HeapBlock* from_cell(const Cell* cell)
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{
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return reinterpret_cast<HeapBlock*>((FlatPtr)cell & ~(block_size - 1));
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}
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Cell* cell_from_possible_pointer(FlatPtr pointer)
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{
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if (pointer < reinterpret_cast<FlatPtr>(m_storage))
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return nullptr;
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size_t cell_index = (pointer - reinterpret_cast<FlatPtr>(m_storage)) / m_cell_size;
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if (cell_index >= cell_count())
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return nullptr;
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return cell(cell_index);
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}
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private:
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HeapBlock(Heap&, size_t cell_size);
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struct FreelistEntry final : public Cell {
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FreelistEntry* next { nullptr };
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virtual const char* class_name() const override { return "FreelistEntry"; }
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};
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Cell* cell(size_t index)
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{
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return reinterpret_cast<Cell*>(&m_storage[index * cell_size()]);
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}
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FreelistEntry* init_freelist_entry(size_t index)
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{
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return new (&m_storage[index * cell_size()]) FreelistEntry();
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}
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Heap& m_heap;
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size_t m_cell_size { 0 };
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FreelistEntry* m_freelist { nullptr };
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u8 m_storage[];
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};
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}
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