[CSE]  Advanced Operating Systems 
 COMP9242 2004/S2 

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M8: ELF Loading

This requires that when creating a process, its code and data section are loaded from the file system into some free memory, and a page table is set up which will satisfy page faults to the text and data sections from the correct frames. The OS's loader must interpret the contents of the executable file (in ELF format). Sample code for reading ELF files is provided.

By this final milestone you should ensure that all I/O is asynchronous. This means that your system must not block waiting on completion of file system or paging I/O, but should be able to run any process that is ready while other processes are blocked on I/O completion.


You have been supplied with code to handle parsing ELF files.

Design issues

One design decision is whether to load the whole executable image on process creation, or instead load page-wise on demand at page-fault time.

You will need to change your build system so that executables are no longer added to the DIT image, but rather copied into your /tftpboot directory.

You will also need to change the way in which your executables are linked. The current makefile links each executable at a different offset within the DIT image, so that all of them can be executed in place. The -T linker option can be used to specify the link address for your executables. In your own interest, do not map the text section to page zero! If you make sure that page zero never needs to be mapped, you can catch most uses of uninitialised pointers -- a great help in debugging!


You will demonstrate (by running a sosh) that your system works even with repeated and concurrent executions, and that you can execute every file (of the right contents) from your NFS directory.

Last modified: 27 Sep 2004.