MaskRay added a comment. In D148573#4277573 <https://reviews.llvm.org/D148573#4277573>, @peter.smith wrote:
> As it stands I think this may have problems with -mbranch-protection. In that > case we'll need a `BTI c` to be the target of the indirect branch. I'm > guessing something like: > > _Z3funv > BTI C ; In hint space > B . + 8 > .word .L__llvm_rtti_proxy-_Z3funv > > Otherwise when the indirect call is made then it will fail on a system with > BTI enabled. > > Not too sure how much of a problem this is for the implementation. The `BTI > c` can't be used as a signature, I guess the code in the caller could check > the value at `_z3funv + 4` . The feature could be marked as incompatible with > `-mbranch-protection`. I guess it may not work well with patchable functions > either. > > I would expect the emitGlobalConstant to emit data. This would be visible in > the object file as we'd have: > > $d > <signature> > <rtti> > $x > instructions. > > At the moment I don't think that this would affect anything except > disassemblers, and the LLD cortex-a53 eratta work around which excludes $d > from the disassembly. It is something that it could be worth fixing, > expecially if there is a `BTI C` involved. Thanks. I forgot to check this interaction with `-mbranch-protection=bti`. x86 `-fcf-protection=branch` has a similar problem. The current AArch64 bti instrumentation always adds a bti (even for local linkage functions that are not taken addresses) to accommodate range extension thunks, but I can think of possible improvement to make `bti` optional in more cases in the future. I think `-fsanitize=function` has to do something similar to `-fsanitize=kcfi` by moving the two words before the function entry: D148665 <https://reviews.llvm.org/D148665> Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D148573/new/ https://reviews.llvm.org/D148573 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
