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Was: [PATCH RFC bpf-next 1/3] bpf: report probe fault to BPF stderr To: Alexei Starovoitov Cc: Andrii Nakryiko , Kumar Kartikeya Dwivedi , Menglong Dong , Menglong Dong , Alexei Starovoitov , bpf , LKML , linux-trace-kernel , jiang.biao@linux.dev References: <20250927061210.194502-1-menglong.dong@linux.dev> <20250927061210.194502-2-menglong.dong@linux.dev> <3571660.QJadu78ljV@7950hx> <7f28937c-121a-4ea8-b66a-9da3be8bccad@gmail.com> <405caf71-315d-46a4-af35-c1fd53470b91@gmail.com> Content-Language: en-US From: Leon Hwang In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 2025/10/9 22:45, Alexei Starovoitov wrote: > On Thu, Oct 9, 2025 at 7:15 AM Leon Hwang wrote: >> >> >> The verifier can rewrite 'bpf_reg_aux()' into the following instructions: >> >> dst_reg = BPF_REG_AUX; >> BPF_REG_AUX = 0; /* clear BPF_REG_AUX */ >> >> As for the architecture-specific implementation, BPF_REG_AUX can be >> mapped to an appropriate register per arch — for example, r11 on x86_64. > > it's taken. There are no free registers. Understood. It would certainly be beneficial if there were available registers on x86_64, as that would enable certain optimizations and improvements. In a similar direction, I have been exploring the idea of introducing a dedicated BPF_REG_TAIL_CALL register to unify the handling of tail_call_cnt in the verifier. This could help standardize the logic across architectures, particularly for those that already employ a dedicated register for tail calls, and allow JIT backends to simplify their tail call implementations accordingly. Thanks, Leon