Reject aligned attribute on bit fields in struct types#585
Open
xavierleroy wants to merge 1 commit into
Open
Conversation
Just like we already reject `_Alignas(N)` on bit fields. Alignment on bit fields was already ignored by the verified part of CompCert.
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Currently, we reject
_Alignas(N)on bit fields, as per ISO C, but tolerateattribute((aligned(N))). However:The verified part of CompCert (Ctypes.v) explicitly ignores alignment specifiers on the types of bit fields.
The unverified part (Cutils.ml) implicitly honors alignment specifiers on the types of bit fields in one place (function
Cutil.sizeof_layout_struct). This can cause__builtin_offsetofand some rare uses ofsizeofto return results that are inconsistent with the actual layout done in Ctypes.v.There is no specification of struct member layout that includes bit-fields with alignment specifiers. The ELF ABI says nothing about this. GCC and Clang do something, but it's unclear what they do.
It seems safer to just report an error for
attribute((aligned(N)))on bit-fields.Issue reported by Christos Papakonstantinou (Cantina Security).