Re: [PATCH v1] rust: cfi: only 64-bit arm and x86 support CFI_CLANG

[Alice Ryhl]

On Mon, Sep 8, 2025 at 3:13 PM Conor Dooley <conor@xxxxxxxxxx> wrote:
>
> From: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
>
> The kernel uses the standard rustc targets for non-x86 targets, and out
> of those only 64-bit arm's target has kcfi support enabled. For x86, the
> custom 64-bit target enables kcfi.
>
> The HAVE_CFI_ICALL_NORMALIZE_INTEGERS_RUSTC config option that allows
> CFI_CLANG to be used in combination with RUST does not check whether the
> rustc target supports kcfi. This breaks the build on riscv (and
> presumably 32-bit arm) when CFI_CLANG and RUST are enabled at the same
> time.
>
> Ordinarily, a rustc-option check would be used to detect target support
> but unfortunately rustc-option filters out the target for reasons given
> in commit 46e24a545cdb4 ("rust: kasan/kbuild: fix missing flags on first
> build"). As a result, if the host supports kcfi but the target does not,
> e.g. when building for riscv on x86_64, the build would remain broken.
>
> Instead, make HAVE_CFI_ICALL_NORMALIZE_INTEGERS_RUSTC depend on the only
> two architectures where the target used supports it to fix the build.
>
> CC: stable@xxxxxxxxxxxxxxx
> Fixes: ca627e636551e ("rust: cfi: add support for CFI_CLANG with Rust")
> Signed-off-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>

Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>