refactor: memcpy to std::ranges::copy to work around ubsan warn#305
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ryanofsky merged 1 commit intoJul 13, 2026
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Failure should look roughly like: |
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Concept ACK on replacing |
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ACK fac7b9b I was also able to reproduce the error that the new test triggers. |
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Code review ACK fac7b9b. Thanks for the fix!
It's still not completely clear to me if this purely a ubsan issue or if there could have been real problems here with compiler optimizations. For example https://developers.redhat.com/articles/2024/12/11/making-memcpynull-null-0-well-defined would seem to suggest that compilers could have used this memcpy to falsely assume result.begin() and data.init() are never null and skip null checks in nearby code. But avoiding memcpy is an improvement in any case.
Possible followups to this change:
- There are also other uses of memcpy in the codebase that could be replaced
- Code would be simpler without the
resultvariable, just usingcopy(value, output.init(value.size())
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I am sure the second arg is the beginning of the destination range, so it would have been: std::ranges::copy(value, output.init(value.size()).begin());
In the past, this was certainly UB in theory (not sure if a compiler exists in practise to exploit this). I think it is fixed in C29, but it is not clear how fast compilers will apply this fix. (Ref: bitcoin/bitcoin#32016 (comment))
Also checked them, but I think they are fine (no promise though). There is https://clang.llvm.org/extra/clang-tidy/checks/modernize/use-ranges.html that can be used? Happy to take a look there, if you find it worthwhile. |
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Actually, this is unrelated. That check is about moving iterator-based algos to range-based ones. For the memcpy replacement, there is llvm/llvm-project#22583 |
fanquake
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Jul 14, 2026
e8de5c7b68 Merge bitcoin-core/libmultiprocess#305: refactor: memcpy to std::ranges::copy to work around ubsan warn 9307e68e5a Merge bitcoin-core/libmultiprocess#306: doc: Bump version 12 > 13 fac7b9b7f6 refactor: memcpy to std::ranges::copy to work around ubsan warn 1bd7025609 Merge bitcoin-core/libmultiprocess#297: test: add map serialization round-trip coverage 438fdd243d doc: Bump version 12 > 13 463d073cb8 test: rename vBool to vector_bool 85df233845 test: add mapStringInt to foo.capnp to cover map serialization and deserialization git-subtree-dir: src/ipc/libmultiprocess git-subtree-split: e8de5c7b68e0ae21c94ae92aa22e5c3b213f9c12
maflcko
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Jul 17, 2026
This avoids a std::span ctor. Recommended in bitcoin-core#305 (review)
maflcko
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Jul 17, 2026
I think there is no issue of passing a nullptr here, but it makes sense to use the std-lib copy for consistency. Recommended in bitcoin-core#305 (review)
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Using std::ranges::copy from the C++ standard library has a few benefits here:
This should also fix bitcoin/bitcoin#35118 (comment)