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Chunks
The chunk has two sections - the metadata of the chunk (information about the chunk) and the user data, where the data is actually stored.
size is fairly self-explanatory - it's the overall size of the chunk.The flags
A, M and P have special uses. P is the PREV_INUSE flag, which is 0 when the previous adjacent chunk (the chunk ahead) is free. M and P are used for more sophisticated heap attacks, so we won't worry about them just yet.prev_size is set if the previous adjacent chunk is free, as calculated by P. If it is not, the heap saves space and prev_size is part of the previous chunk's user data. If it is, then prev_size stores the size of the previous chunk.
A free chunk looks a bit different:
The first part is the same, but
FD and BK pointers have been added. This is for the purpose of sorting them into bins, which we will come onto soon.Last modified 3yr ago