lenary added a comment. In D84414#2234255 <https://reviews.llvm.org/D84414#2234255>, @zzheng wrote:
> In D84414#2234112 <https://reviews.llvm.org/D84414#2234112>, @lenary wrote: > >> Why do we have to pass `-ffixed-x18` when compiling? Is it enough to just >> reserve `x18` whenever the function has the shadow call stack attribute? > > When SCS is on, x18 must be preserved across calls. Given it's a > callee-saved, value in x18 is preserved by functions that do not have SCS > attribute. > > However, saving x18 on stack risks leaking SCS's location in memory, making > the defense useless. Ok, so any compilation units without `-fsanitize=shadow-call-stack` should be compiled with `-ffixed-x18` if you want to link those together. That is reasonable. My question was whether we can ensure that `-fsanitize=shadow-call-stack` can imply `-ffixed-x18` rather than having to pass both options. It is my understanding that all functions in a CU with `-fsanitize=shadow-call-stack` will get the SCS function attribute, so why can't we use that attribute to work out whether x18 should be reserved, rather than using `-ffixed-x18`? You'll see `RISCVRegisterInfo::getReservedRegs` reserves `fp` and `bp` only if they're needed by the function (which can be based on attributes or other info), rather than using `isRegisterReservedByUser` - which seems cleaner to me. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D84414/new/ https://reviews.llvm.org/D84414 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
