I looked at trying to implement -fbounds-safety and -Wunsafe-buffer on a reasonably large codebase (4,000 C and C++ files), and it's basically impossible.
You have to instrument every single file. It can be done in stages though. Just turn the flag on one-by-one for each file. The xnu kernel is _mostly_ instrumented with -fbounds-safety.
Plug: In theory you could auto-convert to a memory-safe subset of C++ as a build step. Auto-converted code would have some run-time overhead, but you can mark any performance-sensitive parts of the code to be exempt from conversion. And you get lifetime and type safety too. For full coverage, performance-sensitive parts of the code can be manually converted to the safe subset to minimize overhead. (Interfaces in extern C blocks remain unconverted by default to maintain ABI compatibility.)
This sounds like the kind of low-thought pattern-based repetitive task where you could tell an LLM to do it and almost certainly expect a fully correct result (and for it to find some bugs along the way), especially if there's some test coverage for it to verify itself against. If you're skeptical, you could tell it to do it on some files you've already converted by hand and compare the results. This kind of thing was a slam dunk for an LLM even a year or two ago.
Because it can only catch a subset of issues, it’s not guaranteed to catch issues (probabilistic), even issues it “could” catch may not be caught due to temporal distance of the free and a subsequent use, and requires the use of a different allocator that supports it. It’s also unclear to me how it know whether a given free is for a sampled or unsampled region - I suspect it must capture all free/realloc to accomplish that but it does imply all of these are sampled.
It’s nowhere near the same as robust bounds checking.
hoyhoy|10 days ago
You have to instrument every single file. It can be done in stages though. Just turn the flag on one-by-one for each file. The xnu kernel is _mostly_ instrumented with -fbounds-safety.
safercplusplus|10 days ago
[1]: https://duneroadrunner.github.io/scpp_articles/PoC_autotrans...
jimmaswell|10 days ago
adrianN|11 days ago
vlovich123|10 days ago
It’s nowhere near the same as robust bounds checking.
hoyhoy|10 days ago