pfelf, interpreters, elfunwindinfo: refactor to not use mmap #909
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instead read the section and program header data using io.ReaderAt
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Do not allow large data reads from reads from the section and program headers. Instead use io.ReaderAt to access this data.
This removes the usage of mmap in pfelf. This is motivated by the fact, that if using mmap, we have no good control over how the RSS explodes. This caused extra complexity to try to madvice the unneeded pages, and additional things to not reference data in the mmap area. Also mmapped data may get changed in the file after validation, so this adds an extra layer of security.
A new cache
pfatbufis added. The concept is to be able to create this on stack, and use it to cache the reads so that the users can access the cache buffers directly without copying. It is also essential that multiple caches can be created so the localized reads go to the same cache. The performance impact is still measurable (2-4x slower or so) depending how the cache works. Further research might be needed to allow tuning the cache better for different portions (sequential vs. random access patterns).cc @florianl @christos68k
fixes #648