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Understanding Load Segments in Executables: Disk to Memory Transition

Explore how load segments in executables transition from disk to virtual memory. Learn about read and zero actions for specific memory segments, including code, read-only data, and global data. Discover how Pintos's load_segment code simplifies the process.

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Understanding Load Segments in Executables: Disk to Memory Transition

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  1. Anatomy of an Executable (‘write-boundary’) 12577 On Disk: 12847 0 4096 8192 12288 41721 ….. In Virtual Memory: what load_segment says you should zero what load_segment says you should read 8048000 8049000 804A000 804B000 804C000 804D000 804E000 read only read/write Code and Read-Only Data Other sections: Debugging Info, etc. Initialized Global Data Uninitialized Global Data (Must Zero) “impurities” – the content of these areas is undefined as far as the program is concerned. For simplicity, they can be filled with data from the executable – this allows all page-in operation to read 4096 (PGSIZE) bytes from a file offset that is a multiple of PGSIZE. This is useful for filesystems that use a 4096 byte blocksize – you only need to store the block number and have all information for a page-in. Pintos’s load_segment code computes offsets that are multiples of 4096; it also computes for you how many bytes should be read from that offset, as shown above. Not drawn to scale Note: the specific numbers came from an older version of our toolchain; they should be ignored. The principle hasn’t changed.

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