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c86df29d11
The dispatcher function is currently abusing the ftrace __fentry__ call location for its own purposes -- this obviously gives trouble when the dispatcher and ftrace are both in use. A previous solution tried using __attribute__((patchable_function_entry())) which works, except it is GCC-8+ only, breaking the build on the earlier still supported compilers. Instead use static_call() -- which has its own annotations and does not conflict with ftrace -- to rewrite the dispatch function. By using: return static_call()(ctx, insni, bpf_func) you get a perfect forwarding tail call as function body (iow a single jmp instruction). By having the default static_call() target be bpf_dispatcher_nop_func() it retains the default behaviour (an indirect call to the argument function). Only once a dispatcher program is attached is the target rewritten to directly call the JIT'ed image. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Tested-by: Björn Töpel <bjorn@kernel.org> Tested-by: Jiri Olsa <jolsa@kernel.org> Acked-by: Björn Töpel <bjorn@kernel.org> Acked-by: Jiri Olsa <jolsa@kernel.org> Link: https://lkml.kernel.org/r/Y1/oBlK0yFk5c/Im@hirez.programming.kicks-ass.net Link: https://lore.kernel.org/bpf/20221103120647.796772565@infradead.org |
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