We have many places where an ObjectFile subclass will take the
DataExtractor representing the entire binary, create a subsection of
that in a new DataExtractor for processing. For instance, an object file
might have symbol table entries with offsets into the string table. A
common code pattern is to create a DataExtractor representing the string
table, and then pulling out the c-strings based on those offsets from
the string table DataExtractor.
When code does this, it creates a new DataExtractor, copies the
Endianness and Wordsize from the original, copies the DataBufferSP from
the original, and specifies a new start and offset into the DataBuffer.
However, if the binary is actaully stored in a VirtualDataExtractor,
this code pattern loses the correct virtual-to-physical table
translation and will not work correctly. This new method simplifies this
common pattern, and correctly takes a subset of a VirtualDataExtractor.
The current implementation only allows a subset of a
VirtualDataExtractor that is contained within a single virtual entry
(LookupTable entry) and returns a DataExtractor with the corret offsets
calculated from the LookupTable. If we need to a VirtualDataExtractor to
create a Subset DataExtractor representing multiple separate virtual
ranges of data, we'll need to copy over the LookupTable entries that
cover all the bytes, and update them to be relative to the new
VirtualDataExtractor. It's a bit of work, and it's not needed right now,
so I'm not tackling that.
I am working on a larger PR which needs this new method. This PR
contains a unit test that uses it.
rdar://148939795
Introduce VirtualDataExtractor, a DataExtractor subclass that enables
reading data at virtual addresses by translating them to physical buffer
offsets using a lookup table. The lookup table maps virtual address
ranges to physical offsets and enforces boundaries to prevent reads from
crossing entry limits.
The new class inherits from DataExtractor, overriding GetData and
PeekData to provide transparent virtual address translation for most of
the DataExtractor methods. The exception are the unchecked methods, that
bypass those methods and are overloaded as well.
