aaron.ballman added a comment. In D132592#3749567 <https://reviews.llvm.org/D132592#3749567>, @ychen wrote:
> Thanks for taking a look! > > In D132592#3749261 <https://reviews.llvm.org/D132592#3749261>, @aaron.ballman > wrote: > >> Do we have any evidence that users need this level of control or will >> understand how to properly use the attribute? The command line option makes >> sense to me because it's an all-or-nothing flag, but I'm not certain I >> understand the need for per-function control. > > https://github.com/llvm/llvm-project/blob/064a08cd955019da9130f1109bfa534e79b8ec7c/llvm/include/llvm/IR/Function.h#L639-L641, > per-function unwind table entry depends on both nounwind and uwtable. We > have nothrow attribute for nounwind but not nouwtable for uwtable. With this, > a user could use function attributes to control unwind table entry generation > which could only be achieved by inline assembly or writing assembly files > directly. I'd consider this a companion of nothrow. So making them both > per-function attribute seems natural? > >> Also, if a user gets this wrong (applies the attribute where they >> shouldn't), what is the failure mode (does it introduce any exploitable >> behavior)? > > The flag may only suppress unwind table emission instead of causing more, the > lack of unwind table may only stop control flow rather than giving it more > freedom. So I think this is safe from a security perspective. Using it wrong > may cause unnecessary crashes just like any other memory bugs, but not a > malicious binary. Thank you for the explanations, that helped. :-) You're missing all of the semantic tests (that the attr takes no arguments, only applies to function-like things, etc). Also, the subject you picked is `FunctionLike` so you should have some test coverage showing how this works when calling through a function pointer with the attribute (or you should pick a more appropriate subject if that one is wrong). ================ Comment at: clang/include/clang/Basic/AttrDocs.td:4545-4546 +the unwind table entry for the specified function. This attribute is useful for +selectively emitting the unwind table entry on some functions when building with +``-funwind-tables`` compiler option. + }]; ---------------- Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D132592/new/ https://reviews.llvm.org/D132592 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
