From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1FF7DC433E1 for ; Sat, 11 Jul 2020 03:25:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F2EEC2075D for ; Sat, 11 Jul 2020 03:25:33 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="kFppbPfk" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727818AbgGKDZd (ORCPT ); Fri, 10 Jul 2020 23:25:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50750 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726707AbgGKDZd (ORCPT ); Fri, 10 Jul 2020 23:25:33 -0400 Received: from mail-lf1-x144.google.com (mail-lf1-x144.google.com [IPv6:2a00:1450:4864:20::144]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CF66BC08C5DD; Fri, 10 Jul 2020 20:25:32 -0700 (PDT) Received: by mail-lf1-x144.google.com with SMTP id m26so4248591lfo.13; Fri, 10 Jul 2020 20:25:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=qMSo4idQH+SPolfM98YFV7hZJ7GyfP1j4WcHly2pXs4=; b=kFppbPfk+savvEEL0Loyoeq/o5y44V6OUOniX62nrHyX0cM4sjGVvwDLsNaJ0xiSkQ hwJqPo0TolwPpTVTMPbxe1wkl8oJJX99iQbL9ePTIdmJG5alXjHwEURzx2eDvDb6qrHT ZGxo4jRfRGggqg4NHG4kxDyDd8/YDMpbZVt5GFFNbvFm+8tM2J6fX8Cg23YMsH4O6JA2 8FwkS3sCSsiIkuZjMWooI6AFHsFMyF4daMnVUgxRRa0Rf9vXeZdrD9a1FwG707a93XZK UbRHVyAHGx8z7MBXGfqqwqUX5quBApSE5/Y5ec8gqaW3ApeMjgMEiHQyaRnBerPKGDnW B3Ww== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=qMSo4idQH+SPolfM98YFV7hZJ7GyfP1j4WcHly2pXs4=; b=fUNjoPJ5LOwpzEKLRawDFpoVfaQ8mVNp6TeldxVZdny9Iv5xinvGq1GlbGSbVGMvio jXvO3AYBQWZYnOHnxmlwGCIBW2GxUlTGdwJJHaB8Z7zu6+/m/ItdnWFKmlx8A3KRUzOm oDN2nSNVfNOhbGdhZ11HqjfCy/R40v5GI2f5nDxCPaRnZRis46WN4G2IttgNWvr/M2cc gs78/QgHz1zZEOHNkimoYXszrvdf2uaqGZhsoYtnOqSKD54Uzn5UmKPezZZ1PEV6xxMW jsCYsb8OlJGjYgEH3C481PqvjHQQo9sXExRes8fiEG9MJrSSLRKILkNWFPiylpU+fnv7 vUUQ== X-Gm-Message-State: AOAM530cDbYQKgJcd+z6meujGV7Lh5UfJL1i8/ub9qvgS8o5BoDRBgj6 Jr5JcESuG882UaHrD+/SWwKWTShOOv9rohVAFV4= X-Google-Smtp-Source: ABdhPJx59uupfoWI7HifdlqkGoPMj0WN4ZOO3ig2kf4z7rMgwChaH4h/hLf0ccw8eBMXP5AiHrpw1i/r/HZKD9W0Vqo= X-Received: by 2002:a19:8497:: with SMTP id g145mr45076237lfd.73.1594437931323; Fri, 10 Jul 2020 20:25:31 -0700 (PDT) MIME-Version: 1.0 References: <20200702134930.4717-1-maciej.fijalkowski@intel.com> <20200702134930.4717-5-maciej.fijalkowski@intel.com> <20200710235632.lhn6edwf4a2l3kiz@ast-mbp.dhcp.thefacebook.com> In-Reply-To: From: Alexei Starovoitov Date: Fri, 10 Jul 2020 20:25:20 -0700 Message-ID: Subject: Re: [RFC PATCH bpf-next 4/5] bpf, x64: rework pro/epilogue and tailcall handling in JIT To: Maciej Fijalkowski Cc: Alexei Starovoitov , Daniel Borkmann , bpf , Network Development , =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= , "Karlsson, Magnus" Content-Type: text/plain; charset="UTF-8" Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Fri, Jul 10, 2020 at 8:20 PM Alexei Starovoitov wrote: > > Of course you are right. > pop+nop+push is incorrect. > > How about the following instead: > - during JIT: > emit_jump(to_skip_below) <- poke->tailcall_bypass > pop_callee_regs > emit_jump(to_tailcall_target) <- poke->tailcall_target > > - Transition from one target to another: > text_poke(poke->tailcall_target, MOD_JMP, old_jmp, new_jmp) > if (new_jmp != NULL) > text_poke(poke->tailcall_bypass, MOD jmp into nop); > else > text_poke(poke->tailcall_bypass, MOD nop into jmp); One more correction. I meant: if (new_jmp != NULL) { text_poke(poke->tailcall_target, MOD_JMP, old_jmp, new_jmp) text_poke(poke->tailcall_bypass, MOD jmp into nop); } else { text_poke(poke->tailcall_bypass, MOD nop into jmp); }