From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6AC3A32AAB1; Thu, 6 Nov 2025 12:29:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762432184; cv=none; b=OG9iOtd0MqXHfmi4VBA87ihSl3E6oLVEa/aRfsPxG2TLGzupSBgK7ZhjV5f823i90QySJrGlpHTNKUeAylvjOD/KshCuCkbRlvP/gVfZaCVMP+DTTy4UZvnlDl8iLFMTYKYz7p+be/m9uI+wgLV49kelRcBMX8u5sZCiQ/TpVBY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762432184; c=relaxed/simple; bh=tA/9M3ARi9alo/ypAVAeWDUjilXQBiFkWC2MawbGD6I=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=G9iFMtBelOY0vlj6FRNd1uLrJ+8glAWvAAxEufuV24v8RE5CzH8skCxdhQRPs7b+N6gkEmRrZTCarO+0NllqaYx7RrhE2y/KF6ugCic8MOegWcz6aQdTB29tz4/HdTf1C1TRGqqXtbqh6B+luknp9C/62ONrIDspQonCr0U0jXM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=TJ417h+t; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="TJ417h+t" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=nPqBbMUpCv5pTCYTP8O6tM3Iga00IspR1junwdyt1zs=; b=TJ417h+tcI06ZEgaOT1NLNNoy+ CpJdWI0I60n9Gkb+MR5ugJCoVdd0iHoSvZn7nXcnRRYYe9cfxlsy/ANSvEwRjPX5HDXB8Skc5Cpck B4RTbeK4BV5dr2ierYmk66qGXx3E9/joRIMZnNoJ0KLpDoFXu73fjiMNSzki/MZPx0dKdeq0UTq/E kjy2/Gpab2i6qbFTk8wyMTuoMGYMLYsE3sBj2vqOCnAoFSUfYcEYiU+kBZxuihll08SArfd37QLFU lQKBKRZiyyr58inYkw0MaL8FB2/Q5b3C6P2ha9ReX6fYxgoyQYmCIxIOI6BT3tvqaP3KtPOjs/JNV 59dwYK5A==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1vGyFh-00000004G1l-2SOg; Thu, 06 Nov 2025 11:34:08 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 75DD730023C; Thu, 06 Nov 2025 13:29:33 +0100 (CET) Date: Thu, 6 Nov 2025 13:29:33 +0100 From: Peter Zijlstra To: Jiri Olsa Cc: Masami Hiramatsu , Steven Rostedt , Josh Poimboeuf , bpf@vger.kernel.org, linux-trace-kernel@vger.kernel.org, x86@kernel.org, Yonghong Song , Song Liu , Andrii Nakryiko Subject: Re: [PATCHv2 2/4] x86/fgraph,bpf: Fix stack ORC unwind from kprobe_multi return probe Message-ID: <20251106122933.GW4067720@noisy.programming.kicks-ass.net> References: <20251103220924.36371-1-jolsa@kernel.org> <20251103220924.36371-3-jolsa@kernel.org> Precedence: bulk X-Mailing-List: linux-trace-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: <20251103220924.36371-3-jolsa@kernel.org> On Mon, Nov 03, 2025 at 11:09:22PM +0100, Jiri Olsa wrote: > Currently we don't get stack trace via ORC unwinder on top of fgraph exit > handler. We can see that when generating stacktrace from kretprobe_multi > bpf program which is based on fprobe/fgraph. > > The reason is that the ORC unwind code won't get pass the return_to_handler > callback installed by fgraph return probe machinery. > > Solving this by creating stack frame in return_to_handler expected by > ftrace_graph_ret_addr function to recover original return address and > continue with the unwind. > > Also updating the pt_regs data with cs/flags/rsp which are needed for > successful stack retrieval from ebpf bpf_get_stackid helper. > - in get_perf_callchain we check user_mode(regs) so CS has to be set > - in perf_callchain_kernel we call perf_hw_regs(regs), so EFLAGS/FIXED > has to be unset > > Acked-by: Masami Hiramatsu (Google) > Signed-off-by: Jiri Olsa > --- > arch/x86/include/asm/ftrace.h | 5 +++++ > arch/x86/kernel/ftrace_64.S | 8 +++++++- > include/linux/ftrace.h | 10 +++++++++- > 3 files changed, 21 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h > index 93156ac4ffe0..b08c95872eed 100644 > --- a/arch/x86/include/asm/ftrace.h > +++ b/arch/x86/include/asm/ftrace.h > @@ -56,6 +56,11 @@ arch_ftrace_get_regs(struct ftrace_regs *fregs) > return &arch_ftrace_regs(fregs)->regs; > } > > +#define arch_ftrace_partial_regs(regs) do { \ > + regs->flags &= ~X86_EFLAGS_FIXED; \ > + regs->cs = __KERNEL_CS; \ > +} while (0) I lost the plot. Why here and not in asm below? > #define arch_ftrace_fill_perf_regs(fregs, _regs) do { \ > (_regs)->ip = arch_ftrace_regs(fregs)->regs.ip; \ > (_regs)->sp = arch_ftrace_regs(fregs)->regs.sp; \ > diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S > index 367da3638167..823dbdd0eb41 100644 > --- a/arch/x86/kernel/ftrace_64.S > +++ b/arch/x86/kernel/ftrace_64.S > @@ -354,12 +354,17 @@ SYM_CODE_START(return_to_handler) > UNWIND_HINT_UNDEFINED > ANNOTATE_NOENDBR > > + /* Restore return_to_handler value that got eaten by previous ret instruction. */ > + subq $8, %rsp > + UNWIND_HINT_FUNC > + > /* Save ftrace_regs for function exit context */ > subq $(FRAME_SIZE), %rsp > > movq %rax, RAX(%rsp) > movq %rdx, RDX(%rsp) > movq %rbp, RBP(%rsp) > + movq %rsp, RSP(%rsp) > movq %rsp, %rdi > > call ftrace_return_to_handler > @@ -368,7 +373,8 @@ SYM_CODE_START(return_to_handler) > movq RDX(%rsp), %rdx > movq RAX(%rsp), %rax > > - addq $(FRAME_SIZE), %rsp > + addq $(FRAME_SIZE) + 8, %rsp > + > /* > * Jump back to the old return address. This cannot be JMP_NOSPEC rdi > * since IBT would demand that contain ENDBR, which simply isn't so for