From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 BA015611E; Tue, 28 Oct 2025 07:02:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761634967; cv=none; b=uwd+aYIn34ub9dUGcCzjleI7iQNCZiSnEtMGIvcIZDP/fOkwg2bk0svMyn9pdGrpTu3tzvgz2UQ9XqhQnnS2ATITSLPGUuRXqLPUrB8zxS867SA5xS6rO6LzhDxTBI/jGCbFzHG/SlAq6fZXXNfLr22Ak/KwooQSbdNcUNXHVe4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761634967; c=relaxed/simple; bh=up08tc/YUb0cEkc2iUu9WrTdHzt37QPPMWQLPZG4agk=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=VHKFCOjoZobZkve7KUjqgTWsKiLTNcCzk5lcq/vCzv9ZzMExwTpiep9vvRiBXIrLepr9q37qaAt+WY9+uj0aGf15b7bayuDD/n4fv4ZjQxOD4XvD8wuP5ViDv8QWkyUZnUfYwCOF6WY3kos0r+a1GD1HRUwAYnkStday2rg2xuw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=T6bWB3x+; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="T6bWB3x+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1F83FC4CEE7; Tue, 28 Oct 2025 07:02:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1761634967; bh=up08tc/YUb0cEkc2iUu9WrTdHzt37QPPMWQLPZG4agk=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=T6bWB3x+T5QR/GQV8yx2efAldmRDBWtbACpQ7//0PN1QAK2//tWjuM3AdpYkzkFtS I/pwxBhAnXiS1Z3D5qAt7fkqXiTMzDtyqBQ8yIRVsUXOytarKMFJTXkId5UXzXJGRa lxVx7Umiex4WM3/9gJG3dX6GIb+2GzRQSfivOicHppbnv2GEUjbCI3+Li5qLjfkGh9 ECWCK8R6/03eyLNoDFr6otQU9MR+ZJUVCDH3n03fxcpcZYFlY2G3uLEA+JjCf7fZna SlttghSaFm/tIEq5yP8dbuQdFBfdrM9Ko75rUVh7v4ne9HUSC9hYNisl2duPfHH6iw JoMsd5C1wc1Pg== Date: Tue, 28 Oct 2025 16:02:44 +0900 From: Masami Hiramatsu (Google) To: Jiri Olsa Cc: Steven Rostedt , Josh Poimboeuf , Peter Zijlstra , bpf@vger.kernel.org, linux-trace-kernel@vger.kernel.org, x86@kernel.org, Yonghong Song , Song Liu , Andrii Nakryiko Subject: Re: [PATCH 2/3] x86/fgraph,bpf: Fix stack ORC unwind from kprobe_multi return probe Message-Id: <20251028160244.e9675ed2b7b624487e86a1e7@kernel.org> In-Reply-To: <20251027131354.1984006-3-jolsa@kernel.org> References: <20251027131354.1984006-1-jolsa@kernel.org> <20251027131354.1984006-3-jolsa@kernel.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 27 Oct 2025 14:13:53 +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 > > Note I feel like it'd be better to set those directly in return_to_handler, > but Steven suggested setting them later in kprobe_multi code path. Yeah, stacktrace is not always used from the return handler. > > Signed-off-by: Jiri Olsa Thanks for the fix. This looks good to me. Acked-by: Masami Hiramatsu (Google) > --- > 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) > + > #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 > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h > index 7ded7df6e9b5..07f8c309e432 100644 > --- a/include/linux/ftrace.h > +++ b/include/linux/ftrace.h > @@ -193,6 +193,10 @@ static __always_inline struct pt_regs *ftrace_get_regs(struct ftrace_regs *fregs > #if !defined(CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS) || \ > defined(CONFIG_HAVE_FTRACE_REGS_HAVING_PT_REGS) > > +#ifndef arch_ftrace_partial_regs > +#define arch_ftrace_partial_regs(regs) do {} while (0) > +#endif > + > static __always_inline struct pt_regs * > ftrace_partial_regs(struct ftrace_regs *fregs, struct pt_regs *regs) > { > @@ -202,7 +206,11 @@ ftrace_partial_regs(struct ftrace_regs *fregs, struct pt_regs *regs) > * Since arch_ftrace_get_regs() will check some members and may return > * NULL, we can not use it. > */ > - return &arch_ftrace_regs(fregs)->regs; > + regs = &arch_ftrace_regs(fregs)->regs; > + > + /* Allow arch specific updates to regs. */ > + arch_ftrace_partial_regs(regs); > + return regs; > } > > #endif /* !CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS || CONFIG_HAVE_FTRACE_REGS_HAVING_PT_REGS */ > -- > 2.51.0 > -- Masami Hiramatsu (Google)