On Tue, Mar 5, 2024 at 12:58 PM Alice Ryhl <aliceryhl@xxxxxxxxxx> wrote: > > Add flags to support the shadow call stack sanitizer, both in the > dynamic and non-dynamic modes. > > Right now, the compiler will emit the warning "unknown feature specified > for `-Ctarget-feature`: `reserve-x18`". However, the compiler still > passes it to the codegen backend, so the flag will work just fine. Once > rustc starts recognizing the flag (or provides another way to enable the > feature), it will stop emitting this warning. See [1] for the relevant > issue. > > Currently, the compiler thinks that the aarch64-unknown-none target > doesn't support -Zsanitizer=shadow-call-stack, so the build will fail if > you enable shadow call stack in non-dynamic mode. However, I still think > it is reasonable to add the flag now, as it will at least fail the build > when using an invalid configuration, until the Rust compiler is fixed to > list -Zsanitizer=shadow-call-stack as supported for the target. See [2] > for the feature request to add this. > > I have tested this change with Rust Binder on an Android device using > CONFIG_DYNAMIC_SCS. Without the -Ctarget-feature=+reserve-x18 flag, the > phone crashes immediately on boot, and with the flag, the phone appears > to work normally. > > This contains a TODO to add the -Zuse-sync-unwind=n flag. The flag > defaults to n, so it isn't a problem today, but the flag is unstable, so > the default could change in a future compiler release. > > Link: https://github.com/rust-lang/rust/issues/121970 [1] > Link: https://github.com/rust-lang/rust/issues/121972 [2] > Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx> > --- > This patch raises the question of whether we should change the Rust > aarch64 support to use a custom target.json specification. If we do > that, then we can fix both the warning for dynamic SCS and the > build-failure for non-dynamic SCS without waiting for a new version of > rustc with the mentioned issues fixed. If the arm64 maintainers are OK with the warning being triggered in that case: Acked-by: Miguel Ojeda <ojeda@xxxxxxxxxx> Otherwise partially reverting to the `target.json` approach sounds good too. I added the `-Zuse-sync-unwind=n` to the list at https://github.com/Rust-for-Linux/linux/issues/2. Given the default is what we want, I have put it in the "Good to have" section. Cheers, Miguel
