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Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1uuRxp-0000000EmVO-3F3o; Fri, 05 Sep 2025 08:38:34 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 552C530034B; Fri, 05 Sep 2025 10:38:33 +0200 (CEST) Date: Fri, 5 Sep 2025 10:38:33 +0200 From: Peter Zijlstra To: Andrii Nakryiko Cc: Jiri Olsa , Oleg Nesterov , Andrii Nakryiko , bpf , open list , Linux trace kernel , X86 ML , Song Liu , Yonghong Song , John Fastabend , Hao Luo , Steven Rostedt , Masami Hiramatsu , Alan Maguire , David Laight , Thomas =?iso-8859-1?Q?Wei=DFschuh?= , Ingo Molnar Subject: Re: nop5-optimized USDTs WAS: Re: [PATCHv6 perf/core 09/22] uprobes/x86: Add uprobe syscall to speed up uprobe Message-ID: <20250905083833.GR4068168@noisy.programming.kicks-ass.net> References: <20250904203511.GB4067720@noisy.programming.kicks-ass.net> <20250904205210.GQ3245006@noisy.programming.kicks-ass.net> <20250904215617.GR3245006@noisy.programming.kicks-ass.net> <20250904215826.GP4068168@noisy.programming.kicks-ass.net> <20250905082447.GQ4068168@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250905082447.GQ4068168@noisy.programming.kicks-ass.net> On Fri, Sep 05, 2025 at 10:24:47AM +0200, Peter Zijlstra wrote: > +bool insn_is_nop(struct insn *insn) > +{ > + u8 rex, rex_b = 0, rex_x = 0, rex_r = 0, rex_w = 0; > + u8 modrm, modrm_mod, modrm_reg, modrm_rm; > + u8 sib = 0, sib_scale, sib_index, sib_base; > + > + if (insn->rex_prefix.nbytes) { > + rex = insn->rex_prefix.bytes[0]; > + rex_w = !!X86_REX_W(rex); > + rex_r = !!X86_REX_R(rex); > + rex_x = !!X86_REX_X(rex); > + rex_b = !!X86_REX_B(rex); > + } > + > + if (insn->modrm.nbytes) { > + modrm = insn->modrm.bytes[0]; > + modrm_mod = X86_MODRM_MOD(modrm); > + modrm_reg = X86_MODRM_REG(modrm) + 8*rex_r; > + modrm_rm = X86_MODRM_RM(modrm) + 8*rex_b; > + } > + > + if (insn->sib.nbytes) { > + sib = insn->sib.bytes[0]; > + sib_scale = X86_SIB_SCALE(sib); > + sib_index = X86_SIB_INDEX(sib) + 8*rex_x; > + sib_base = X86_SIB_BASE(sib) + 8*rex_b; > + > + modrm_rm = sib_base; > + } > + > + switch (insn->opcode.bytes[0]) { > + case 0x0f: /* 2nd byte */ > + break; > + > + case 0x89: /* MOV */ > + if (modrm_mod != 3) /* register-direct */ > + return false; > + > + if (insn->x86_64 && !rex_w) /* native size */ > + return false; > + > + for (int i = 0; i < insn->prefixes.nbytes; i++) { > + if (insn->prefixes.bytes[i] == 0x66) /* OSP */ > + return false; > + } > + > + return modrm_reg == modrm_rm; /* MOV %reg, %reg */ > + > + case 0x8d: /* LEA */ > + if (modrm_mod == 0 || modrm_mod == 3) /* register-indirect with disp */ > + return false; > + > + if (insn->x86_64 && !rex_w) /* native size */ > + return false; > + > + if (insn->displacement.value != 0) > + return false; > + > + if (sib & (sib_scale != 0 || sib_index != 4)) /* (%reg, %eiz, 1) */ Argh, that should obviously be: && > + return false; > + > + for (int i = 0; i < insn->prefixes.nbytes; i++) { > + if (insn->prefixes.bytes[i] != 0x3e) /* DS */ > + return false; > + } > + > + return modrm_reg == modrm_rm; /* LEA 0(%reg), %reg */ > + > + case 0x90: /* NOP */ > + for (int i = 0; i < insn->prefixes.nbytes; i++) { > + if (insn->prefixes.bytes[i] == 0xf3) /* REP */ > + return false; /* REP NOP -- PAUSE */ > + } > + return true; > + > + case 0xe9: /* JMP.d32 */ > + case 0xeb: /* JMP.d8 */ > + return insn->immediate.value == 0; /* JMP +0 */ > + > + default: > + return false; > + } > + > + switch (insn->opcode.bytes[1]) { > + case 0x1f: > + return modrm_reg == 0; /* 0f 1f /0 -- NOPL */ > + > + default: > + return false; > + } > +}