On Fri, Aug 22, 2025 at 04:05:53PM +0200, Andrea Righi wrote:
> Some distributions (e.g., CachyOS) support building the kernel with -O3,
> but doing so may break kfuncs, resulting in their symbols not being
> properly exported.
>
> In fact, with gcc -O3, some kfuncs may be optimized away despite being
> annotated as noinline. This happens because gcc can still clone the
> function during IPA optimizations, e.g., by duplicating or inlining it
> into callers, and then dropping the standalone symbol. This breaks BTF
> ID resolution since resolve_btfids relies on the presence of a global
> symbol for each kfunc.
>
> Currently, this is not an issue for upstream, because we don't allow
> building the kernel with -O3, but it may be safer to address it anyway,
> to prevent potential issues in the future if compilers become more
> aggressive with optimizations.
>
> Therefore, add __noclone to __bpf_kfunc to ensure kfuncs are never
> cloned and remain distinct, globally visible symbols, regardless of
> the optimization level.
>
> Fixes: 57e7c169cd6af ("bpf: Add __bpf_kfunc tag for marking kernel functions as kfuncs")
> Signed-off-by: Andrea Righi <arighi@xxxxxxxxxx>
Acked-by: David Vernet <void@xxxxxxxxxxxxx>
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