Re: [PATCH] riscv: Require clang-17 or newer for kCFI

Re: [PATCH] riscv: Require clang-17 or newer for kCFI

[Sami Tolvanen]

Hi Nathan,

On Thu, Jun 12, 2025 at 12:57 PM Nathan Chancellor <nathan@kernel.org> wrote:
>
> After the combination of commit c217157bcd1d ("riscv: Implement
> HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS"), which starts using
> '-fpatchable-function-entry=M,N', and commit d0262e907e29 ("riscv:
> ftrace: support PREEMPT"), which allows CONFIG_DYNAMIC_FTRACE to be
> enabled by allmodconfig, allmodconfig builds with clang-16 begin
> crashing in the generic LLVM kCFI pass (see [1] for the stack trace).
>
> clang-17 avoids this crash by moving to target-specific lowering of the
> kCFI operand bundles [2]. Require clang-17 to select CONFIG_CFI_CLANG to
> avoid this crash.
>
> Fixes: c217157bcd1d ("riscv: Implement HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS")
> Link: https://godbolt.org/z/xG39Pn16o [1]
> Link: https://github.com/llvm/llvm-project/commit/62fa708ceb027713b386c7e0efda994f8bdc27e2 [2]
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
>  arch/riscv/Kconfig | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 36061f4732b7..d71ea0f4466f 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -63,7 +63,8 @@ config RISCV
>         select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
>         select ARCH_STACKWALK
>         select ARCH_SUPPORTS_ATOMIC_RMW
> -       select ARCH_SUPPORTS_CFI_CLANG
> +       # clang >= 17: https://github.com/llvm/llvm-project/commit/62fa708ceb027713b386c7e0efda994f8bdc27e2
> +       select ARCH_SUPPORTS_CFI_CLANG if CLANG_VERSION >= 170000
>         select ARCH_SUPPORTS_DEBUG_PAGEALLOC if MMU
>         select ARCH_SUPPORTS_HUGE_PFNMAP if TRANSPARENT_HUGEPAGE
>         select ARCH_SUPPORTS_HUGETLBFS if MMU

LGTM. Thanks!

Reviewed-by: Sami Tolvanen <samitolvanen@google.com>

Sami

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