Stream: wasmtime

Topic: wmemcheck improvements

cobbal (Nov 20 2024 at 23:20):

I was recently tracking down a memory corruption bug in swift and found the wmemcheck tool to be very helpful. Since the runtime of swift is fairly large, it required some extra features to remove false positives. I was able to modify wmemcheck to be useful enough for the job.

I'd like to contribute the changes, many of which overlap with parts of issue https://github.com/bytecodealliance/wasmtime/issues/7037 . In particular, I needed to add the following:

• support for the other memory functions exported by wasi-libc (calloc, realloc, posix_memalign, aligned_alloc, malloc_usable_size)
• tracking memory in 4-byte chunks instead of 1-byte. e.g. wasi-libc's strlen loads strings 4 bytes at a time, and possibly beyond the end of the string for efficiency.
• Disabling the check for reading uninitialized memory.

The last 2 possibly should be hidden behind options, but I'm not familiar enough with the code base or how others use this tool to know what the right approach would be.

I also wasn't quite sure if this should be an issue, a PR, or a comment somewhere, so I'm asking here instead. My current WIP branch is at https://github.com/cobbal/wasmtime/tree/cobbal/wmemcheck-updates

Chris Fallin (Nov 20 2024 at 23:23):

Please do submit a PR, possibly in draft status (but ping/request reviews at least from me)! This is very useful, thanks for pushing this forward and I'm glad it helped you debug some issues!

cobbal (Nov 20 2024 at 23:57):

Chris Fallin said:

Please do submit a PR, possibly in draft status (but ping/request reviews at least from me)! This is very useful, thanks for pushing this forward and I'm glad it helped you debug some issues!

Done! I don't seem to be able to request a review though. https://github.com/bytecodealliance/wasmtime/pull/9641

Chris Fallin (Nov 21 2024 at 00:00):

ah that's likely because you're not a project member, sorry; I'll assign myself and take a look

Last updated: Dec 23 2024 at 13:07 UTC