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Date: Thu, 21 May 2015 18:17:07 +0200 From: Daniel Borkmann <daniel@...earbox.net> To: Alexei Starovoitov <ast@...mgrid.com> CC: "David S. Miller" <davem@...emloft.net>, Ingo Molnar <mingo@...nel.org>, Michael Holzheu <holzheu@...ux.vnet.ibm.com>, Zi Shen Lim <zlim.lnx@...il.com>, linux-api@...r.kernel.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH net-next 1/4] bpf: allow bpf programs to tail-call other bpf programs On 05/20/2015 01:59 AM, Alexei Starovoitov wrote: > introduce bpf_tail_call(ctx, &jmp_table, index) helper function > which can be used from BPF programs like: > int bpf_prog(struct pt_regs *ctx) > { > ... > bpf_tail_call(ctx, &jmp_table, index); > ... > } > that is roughly equivalent to: > int bpf_prog(struct pt_regs *ctx) > { > ... > if (jmp_table[index]) > return (*jmp_table[index])(ctx); > ... > } > The important detail that it's not a normal call, but a tail call. > The kernel stack is precious, so this helper reuses the current > stack frame and jumps into another BPF program without adding > extra call frame. > It's trivially done in interpreter and a bit trickier in JITs. > In case of x64 JIT the bigger part of generated assembler prologue > is common for all programs, so it is simply skipped while jumping. > Other JITs can do similar prologue-skipping optimization or > do stack unwind before jumping into the next program. > ... > Signed-off-by: Alexei Starovoitov <ast@...mgrid.com> LGTM, thanks! Acked-by: Daniel Borkmann <daniel@...earbox.net> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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