On Wed, Dec 13, 2023 at 05:01:07PM +0800, Wang wrote: > On 2023/12/13 16:48, Dan Li wrote: > > + Likun > > > > On Tue, 28 Mar 2023 at 06:18, Sami Tolvanen <samitolvanen@xxxxxxxxxx> wrote: > >> On Mon, Mar 27, 2023 at 2:30 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > >>> On Sat, Mar 25, 2023 at 01:54:16AM -0700, Dan Li wrote: > >>> > >>>> In the compiler part[4], most of the content is the same as Sami's > >>>> implementation[3], except for some minor differences, mainly including: > >>>> > >>>> 1. The function typeid is calculated differently and it is difficult > >>>> to be consistent. > >>> This means there is an effective ABI break between the compilers, which > >>> is sad :-( Is there really nothing to be done about this? > >> I agree, this would be unfortunate, and would also be a compatibility > >> issue with rustc where there's ongoing work to support > >> clang-compatible CFI type hashes: > >> > >> https://github.com/rust-lang/rust/pull/105452 > >> > >> Sami > > > Hi Peter and Sami > > I am Dan Li's colleague, and I will take over and continue the work of CFI. Welcome; this is great news! :) Thanks for picking up the work. > > Regarding the issue of gcc cfi type id being compatible with clang, we > have analyzed and verified: > > 1. clang uses Mangling defined in Itanium C++ ABI to encode the function > prototype, and uses the encoding result as input to generate cfi type id; > 2. Currently, gcc only implements mangling for the C++ compiler, and the > function prototype coding generated by these interfaces is compatible > with clang, but gcc's c compiler does not support mangling.; > > Adding mangling to gcc's c compiler is a huge and difficult task，because > we have to refactor the mangling of C++, splitting it into basic > mangling and language specific mangling, and adding support for the c > language which requires a deep understanding of the compiler and > language processing parts. > > And for the kernel cfi, I suggest separating type compatibility from CFI > basic functions. Type compatibility is independent from CFI basic > funcitons and should be dealt with under another topic. Should we focus > on the main issus of cfi, and let it work first on linux kernel, and > left the compatible issue to be solved later? If you mean keeping the hashes identical between Clang/LLVM and GCC, I think this is going to be a requirement due to adding Rust to the build environment (which uses the LLVM mangling and hashing). FWIW, I think the subset of type mangling needed isn't the entirely C++ language spec, so it shouldn't be hard to add this to GCC. -Kees -- Kees Cook
