From patchwork Wed Oct 27 08:52:59 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Peter Zijlstra X-Patchwork-Id: 12586733 X-Patchwork-Delegate: bpf@iogearbox.net Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 61A00C433EF for ; Wed, 27 Oct 2021 09:00:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 469CE610C8 for ; Wed, 27 Oct 2021 09:00:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236174AbhJ0JC3 (ORCPT ); Wed, 27 Oct 2021 05:02:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52870 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241150AbhJ0JC2 (ORCPT ); Wed, 27 Oct 2021 05:02:28 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 676DEC061745 for ; Wed, 27 Oct 2021 02:00:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Content-Type:MIME-Version:References: Subject:To:From:Date:Message-ID:Sender:Reply-To:Cc:Content-Transfer-Encoding: Content-ID:Content-Description:In-Reply-To; bh=puoZu7p9N+KXOmVqW8fmIuq/VnNO6u9m1U0/aCFiXlc=; b=Ro/2E3PieqKw2KyWhJzUK/fVdD bpASHaNIQtBLM1R64t50trLHngJFQPfUJP4szcPohUBsMvzQE6lVm9Bjwa9Uq+a8usIpHd+YOEaYc Ev3iFtE2H/cePbqMD8Y8hyyRrNWucHL759JtCtqWOvll214QeqK5GqmL52HJYoiGwAIUltIhzLJRb uzCISPsutngyDuqMXUfZScXKG1qleoUKtO15DFljJNXyl1XZLY+vTzS1CVG4CKtWkSpAlzG16Comv n/kLCvMWb3eA6x3M/1Ii6nEG99neplLM3MzTjb2fb06SVGMRYnc9/tLk9w5xe5GiipL/+IDG/NGMV 00YoQvxA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1mfelT-00HWU3-7S for bpf@vger.kernel.org; Wed, 27 Oct 2021 08:58:51 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id C0BB230281E for ; Wed, 27 Oct 2021 10:58:20 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 0) id B10FF236E43D7; Wed, 27 Oct 2021 10:58:20 +0200 (CEST) Message-ID: <20211027085521.137194306@infradead.org> User-Agent: quilt/0.66 Date: Wed, 27 Oct 2021 10:52:59 +0200 From: Peter Zijlstra To: bpf@vger.kernel.org Subject: [PATCH bpf-next 16/17] bpf, x86: Simplify computing label offsets References: <20211027085243.008677168@infradead.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net Take an idea from the 32bit JIT, which uses the multi-pass nature of the JIT to compute the instruction offsets on a prior pass in order to compute the relative jump offsets on a later pass. Application to the x86_64 JIT is slightly more involved because the offsets depend on program variables (such as callee_regs_used and stack_depth) and hence the computed offsets need to be kept in the context of the JIT. This removes, IMO quite fragile, code that hard-codes the offsets and tries to compute the length of variable parts of it. Convert both emit_bpf_tail_call_*() functions which have an out: label at the end. Additionally emit_bpt_tail_call_direct() also has a poke table entry, for which it computes the offset from the end (and thus already relies on the previous pass to have computed addrs[i]), also convert this to be a forward based offset. Signed-off-by: Peter Zijlstra (Intel) --- arch/x86/net/bpf_jit_comp.c | 123 +++++++++++++++----------------------------- 1 file changed, 42 insertions(+), 81 deletions(-) --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -224,6 +224,14 @@ static void jit_fill_hole(void *area, un struct jit_context { int cleanup_addr; /* Epilogue code offset */ + + /* + * Program specific offsets of labels in the code; these rely on the + * JIT doing at least 2 passes, recording the position on the first + * pass, only to generate the correct offset on the second pass. + */ + int tail_call_direct_label; + int tail_call_indirect_label; }; /* Maximum number of bytes emitted while JITing one eBPF insn */ @@ -379,22 +387,6 @@ int bpf_arch_text_poke(void *ip, enum bp return __bpf_arch_text_poke(ip, t, old_addr, new_addr, true); } -static int get_pop_bytes(bool *callee_regs_used) -{ - int bytes = 0; - - if (callee_regs_used[3]) - bytes += 2; - if (callee_regs_used[2]) - bytes += 2; - if (callee_regs_used[1]) - bytes += 2; - if (callee_regs_used[0]) - bytes += 1; - - return bytes; -} - /* * Generate the following code: * @@ -410,29 +402,12 @@ static int get_pop_bytes(bool *callee_re * out: */ static void emit_bpf_tail_call_indirect(u8 **pprog, bool *callee_regs_used, - u32 stack_depth) + u32 stack_depth, u8 *ip, + struct jit_context *ctx) { int tcc_off = -4 - round_up(stack_depth, 8); - u8 *prog = *pprog; - int pop_bytes = 0; - int off1 = 42; - int off2 = 31; - int off3 = 9; - - /* count the additional bytes used for popping callee regs from stack - * that need to be taken into account for each of the offsets that - * are used for bailing out of the tail call - */ - pop_bytes = get_pop_bytes(callee_regs_used); - off1 += pop_bytes; - off2 += pop_bytes; - off3 += pop_bytes; - - if (stack_depth) { - off1 += 7; - off2 += 7; - off3 += 7; - } + u8 *prog = *pprog, *start = *pprog; + int offset; /* * rdi - pointer to ctx @@ -447,8 +422,9 @@ static void emit_bpf_tail_call_indirect( EMIT2(0x89, 0xD2); /* mov edx, edx */ EMIT3(0x39, 0x56, /* cmp dword ptr [rsi + 16], edx */ offsetof(struct bpf_array, map.max_entries)); -#define OFFSET1 (off1 + RETPOLINE_RCX_BPF_JIT_SIZE) /* Number of bytes to jump */ - EMIT2(X86_JBE, OFFSET1); /* jbe out */ + + offset = ctx->tail_call_indirect_label - (prog + 2 - start); + EMIT2(X86_JBE, offset); /* jbe out */ /* * if (tail_call_cnt > MAX_TAIL_CALL_CNT) @@ -456,8 +432,9 @@ static void emit_bpf_tail_call_indirect( */ EMIT2_off32(0x8B, 0x85, tcc_off); /* mov eax, dword ptr [rbp - tcc_off] */ EMIT3(0x83, 0xF8, MAX_TAIL_CALL_CNT); /* cmp eax, MAX_TAIL_CALL_CNT */ -#define OFFSET2 (off2 + RETPOLINE_RCX_BPF_JIT_SIZE) - EMIT2(X86_JA, OFFSET2); /* ja out */ + + offset = ctx->tail_call_indirect_label - (prog + 2 - start); + EMIT2(X86_JA, offset); /* ja out */ EMIT3(0x83, 0xC0, 0x01); /* add eax, 1 */ EMIT2_off32(0x89, 0x85, tcc_off); /* mov dword ptr [rbp - tcc_off], eax */ @@ -470,12 +447,11 @@ static void emit_bpf_tail_call_indirect( * goto out; */ EMIT3(0x48, 0x85, 0xC9); /* test rcx,rcx */ -#define OFFSET3 (off3 + RETPOLINE_RCX_BPF_JIT_SIZE) - EMIT2(X86_JE, OFFSET3); /* je out */ - *pprog = prog; - pop_callee_regs(pprog, callee_regs_used); - prog = *pprog; + offset = ctx->tail_call_indirect_label - (prog + 2 - start); + EMIT2(X86_JE, offset); /* je out */ + + pop_callee_regs(&prog, callee_regs_used); EMIT1(0x58); /* pop rax */ if (stack_depth) @@ -495,38 +471,18 @@ static void emit_bpf_tail_call_indirect( RETPOLINE_RCX_BPF_JIT(); /* out: */ + ctx->tail_call_indirect_label = prog - start; *pprog = prog; } static void emit_bpf_tail_call_direct(struct bpf_jit_poke_descriptor *poke, - u8 **pprog, int addr, u8 *image, - bool *callee_regs_used, u32 stack_depth) + u8 **pprog, u8 *ip, + bool *callee_regs_used, u32 stack_depth, + struct jit_context *ctx) { int tcc_off = -4 - round_up(stack_depth, 8); - u8 *prog = *pprog; - int pop_bytes = 0; - int off1 = 20; - int poke_off; - - /* count the additional bytes used for popping callee regs to stack - * that need to be taken into account for jump offset that is used for - * bailing out from of the tail call when limit is reached - */ - pop_bytes = get_pop_bytes(callee_regs_used); - off1 += pop_bytes; - - /* - * total bytes for: - * - nop5/ jmpq $off - * - pop callee regs - * - sub rsp, $val if depth > 0 - * - pop rax - */ - poke_off = X86_PATCH_SIZE + pop_bytes + 1; - if (stack_depth) { - poke_off += 7; - off1 += 7; - } + u8 *prog = *pprog, *start = *pprog; + int offset; /* * if (tail_call_cnt > MAX_TAIL_CALL_CNT) @@ -534,28 +490,30 @@ static void emit_bpf_tail_call_direct(st */ EMIT2_off32(0x8B, 0x85, tcc_off); /* mov eax, dword ptr [rbp - tcc_off] */ EMIT3(0x83, 0xF8, MAX_TAIL_CALL_CNT); /* cmp eax, MAX_TAIL_CALL_CNT */ - EMIT2(X86_JA, off1); /* ja out */ + + offset = ctx->tail_call_direct_label - (prog + 2 - start); + EMIT2(X86_JA, offset); /* ja out */ EMIT3(0x83, 0xC0, 0x01); /* add eax, 1 */ EMIT2_off32(0x89, 0x85, tcc_off); /* mov dword ptr [rbp - tcc_off], eax */ - poke->tailcall_bypass = image + (addr - poke_off - X86_PATCH_SIZE); + poke->tailcall_bypass = ip + (prog - start); poke->adj_off = X86_TAIL_CALL_OFFSET; - poke->tailcall_target = image + (addr - X86_PATCH_SIZE); + poke->tailcall_target = ip + ctx->tail_call_direct_label - X86_PATCH_SIZE; poke->bypass_addr = (u8 *)poke->tailcall_target + X86_PATCH_SIZE; emit_jump(&prog, (u8 *)poke->tailcall_target + X86_PATCH_SIZE, poke->tailcall_bypass); - *pprog = prog; - pop_callee_regs(pprog, callee_regs_used); - prog = *pprog; + pop_callee_regs(&prog, callee_regs_used); EMIT1(0x58); /* pop rax */ if (stack_depth) EMIT3_off32(0x48, 0x81, 0xC4, round_up(stack_depth, 8)); memcpy(prog, x86_nops[5], X86_PATCH_SIZE); prog += X86_PATCH_SIZE; + /* out: */ + ctx->tail_call_direct_label = prog - start; *pprog = prog; } @@ -1404,13 +1362,16 @@ st: if (is_imm8(insn->off)) case BPF_JMP | BPF_TAIL_CALL: if (imm32) emit_bpf_tail_call_direct(&bpf_prog->aux->poke_tab[imm32 - 1], - &prog, addrs[i], image, + &prog, image + addrs[i - 1], callee_regs_used, - bpf_prog->aux->stack_depth); + bpf_prog->aux->stack_depth, + ctx); else emit_bpf_tail_call_indirect(&prog, callee_regs_used, - bpf_prog->aux->stack_depth); + bpf_prog->aux->stack_depth, + image + addrs[i - 1], + ctx); break; /* cond jump */