netdev - Re: [PATCH bpf 0/2] Limit tail calls to 33 in all JIT compilers

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Message-ID: <20191210181929.477nstc4vcccecyc@kafai-mbp>
Date:   Tue, 10 Dec 2019 18:19:32 +0000
From:   Martin Lau <kafai@...com>
To:     Paul Chaignon <paul.chaignon@...nge.com>
CC:     Paul Burton <paulburton@...nel.org>,
        Björn Töpel <bjorn.topel@...il.com>,
        Mahshid Khezri <khezri.mahshid@...il.com>,
        "paul.chaignon@...il.com" <paul.chaignon@...il.com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>
Subject: Re: [PATCH bpf 0/2] Limit tail calls to 33 in all JIT compilers

On Mon, Dec 09, 2019 at 07:51:52PM +0100, Paul Chaignon wrote:
> The BPF interpreter and all JIT compilers, except RISC-V's and MIPS',
> enforce a 33-tail calls limit at runtime.  Because of this discrepancy, a
> BPF program can have a different behavior and output depending on whether
> it is interpreted or JIT compiled, or depending on the underlying
> architecture.
> 
> This patchset changes the RISC-V and MIPS JIT compilers to limit tail
> calls to 33 instead of 32.  I have checked other BPF JIT compilers for the
> same discrepancy.
Acked-by: Martin KaFai Lau <kafai@...com>