Alpoyo / aos-labs-2023-rbtree

The AOS implementation

The kernel main function is setup to do a randomized test on the rbtree. It randomly shuffles 15 integers -> inserts those integers into the rbtree -> attempts to remove all the nodes in order of index in randomized array. main() should print "You should see this message!\n" after the randomized test, but fails because it crashes. Run via make qemu-nox.

The exact steps are visualized in rbtree_aos.pdf. From what we can see in this case, the insertion seems to go right but deletion violates some properties of the redblack tree, which results in a crash in a later removal. rbtree_linux.pdf shows for reference how the linux implementation performs insertions and then deletions for the same order of operations.

gdb steps to get into the offending rb_remove() call:

b main.c:75
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The Linux implementation

To solve the rbtree problem for our openLSD OS, we ripped the linux kernel's implementation for rbtree and slightly modified it to comply with OpenLSD's interface for rbtree operations. You can switch to the linux branch and run make qemu-nox to see that the randomized test does indeed work with this implementation.

Testing suite

We have added a testing suite for rbtree, which we used to validate the linux implementation after translating.

• cd into rbtree_tests and build with make aos or make linux, for aos and linux implementations respectively.
• Test with ./rbtree_test <test_index> where <test_index> is an integer in the range [0, 6]. Each test will output .png images of each step, which is the method we used to create rbtree_aos.pdf and rbtree_linux.pdf.
• Use make pdf to turn the image sequence into a single pdf and make clean to cleanup all the files. The dependencies are dot and convert for the testing suite.
• Testing parameters can be adjusted in test.c by changing the constants defined at the top of the file.

Questions

• please email me at: [e-mail]