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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5841ECD13D2 for ; Wed, 29 Apr 2026 15:26:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Lkm0lfKEDuqhzeWjwT5+p/LQIt4rwROCyMCOGCvE1F8=; b=W0Yg08tU0g0LqNGqtxWsXXIanX 4/2ZHtXk7MQqRF9/AaoEda5GXm0EX/VLSY2rox9CpI1hltYgYPVbli3BYdWLZpht2hGkNXECI4A1U 6TjJOgnt0OFTOZFjIL1LHboYiwSb3YFLjKmqpUN36orql3ehJPwJ8Y0wDp4LFRmXPlTTBo3gTfdLp LsyKdDXxW0VPOFvLbdpbvYvd65bXAVtAqA1RasA0DNyFe/TP9USU8w5vGFbIRh4bugRS6IaAgh3dl xLVEfrOtcvfkfX5IzVrJxZdtwiyr9harfQ0GvtXJZd78fR4ReCk14zw72KtnnIKMz7obB1O2VTYQJ caDDjxwQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1wI6o2-00000003q5I-0Hhq; Wed, 29 Apr 2026 15:26:30 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1wI6nz-00000003q3N-2XWn for linux-arm-kernel@lists.infradead.org; Wed, 29 Apr 2026 15:26:28 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B75ED1655; Wed, 29 Apr 2026 08:26:15 -0700 (PDT) Received: from J2N7QTR9R3.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9B3003F763; Wed, 29 Apr 2026 08:26:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1777476381; bh=ToHBbsGGf1LD2+ZDgJuZjsnXK7XLE8KJHIPpOy6olpM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=DVR5A69YL3Q+LStcdhQecow5PpoUUUb3PLHRQdvqty0reh/1ncGgWmmiKXTgSK9At XIdCnhZ+gv3B2UuYEsOdIL7aGkJe8GNfPRLmDsFxcY58+0G23kboLqTRD4D64V94BA 62YpRlDnNvetzvGDJ3vs9upWOmCgsx1CCaeQVYAw= Date: Wed, 29 Apr 2026 16:26:12 +0100 From: Mark Rutland To: Dylan Hatch Cc: Roman Gushchin , Weinan Liu , Will Deacon , Josh Poimboeuf , Indu Bhagat , Peter Zijlstra , Steven Rostedt , Catalin Marinas , Jiri Kosina , Jens Remus , Prasanna Kumar T S M , Puranjay Mohan , Song Liu , joe.lawrence@redhat.com, linux-toolchains@vger.kernel.org, linux-kernel@vger.kernel.org, live-patching@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Randy Dunlap Subject: Re: [PATCH v5 3/8] arm64: entry: add unwind info for various kernel entries Message-ID: References: <20260428183643.3796063-1-dylanbhatch@google.com> <20260428183643.3796063-4-dylanbhatch@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260428183643.3796063-4-dylanbhatch@google.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260429_082627_731666_7A06E660 X-CRM114-Status: GOOD ( 24.23 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Dylan, On Tue, Apr 28, 2026 at 06:36:38PM +0000, Dylan Hatch wrote: > From: Weinan Liu > > DWARF CFI (Call Frame Information) specifies how to recover the return > address and callee-saved registers at each PC in a given function. > Compilers are able to generate the CFI annotations when they compile > the code to assembly language. For handcrafted assembly, we need to > annotate them by hand. > > Annotate minimal CFI to enable stacktracing using SFrame for kernel > exception entries through el1*_64_*() paths I thought we were only consuming SFrame when unwinding an exeption boundary? We shouldn't be taking exceptions _from_ the entry assembly functions unless something has gone horribly wrong, and so I don't see why we'd need CFI entries for the entry assembly functions. Am I missing some reason we need CFI entries for the entry assembly functions? I strongly suspect it is not necessary to add these, and I'd prefer to omit them. > and irq entries through call_on_irq_stack() Needing some sort of unwind annotations for call_on_irq_stack() makes sense to me, but don't we need something for other assembly functions too? We can interrupt things like memset(); I assume we'll treat those as unreliable until annotated? Mark. > Signed-off-by: Weinan Liu > Suggested-by: Jens Remus > Reviewed-by: Jens Remus > Signed-off-by: Dylan Hatch > --- > arch/arm64/kernel/entry.S | 23 +++++++++++++++++++++++ > 1 file changed, 23 insertions(+) > > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index f8018b5c1f9a..dc55b0b19cfa 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -30,6 +30,12 @@ > #include > #include > > +/* > + * Do not generate .eh_frame. Only generate .debug_frame and optionally > + * .sframe (via assembler option --gsframe[-N]). > + */ > + .cfi_sections .debug_frame > + > .macro clear_gp_regs > .irp n,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29 > mov x\n, xzr > @@ -575,7 +581,16 @@ SYM_CODE_START_LOCAL(el\el\ht\()_\regsize\()_\label) > .if \el == 0 > b ret_to_user > .else > + /* > + * Minimal DWARF CFI for unwinding across the call above. > + * Enable unwinding for el1*_64_*() path only. > + */ > + .cfi_startproc > + .cfi_def_cfa_offset PT_REGS_SIZE > + .cfi_offset 29, S_FP - PT_REGS_SIZE > + .cfi_offset 30, S_LR - PT_REGS_SIZE > b ret_to_kernel > + .cfi_endproc > .endif > SYM_CODE_END(el\el\ht\()_\regsize\()_\label) > .endm > @@ -872,6 +887,7 @@ NOKPROBE(ret_from_fork) > * Calls func(regs) using this CPU's irq stack and shadow irq stack. > */ > SYM_FUNC_START(call_on_irq_stack) > + .cfi_startproc > save_and_disable_daif x9 > #ifdef CONFIG_SHADOW_CALL_STACK > get_current_task x16 > @@ -882,6 +898,9 @@ SYM_FUNC_START(call_on_irq_stack) > /* Create a frame record to save our LR and SP (implicit in FP) */ > stp x29, x30, [sp, #-16]! > mov x29, sp > + .cfi_def_cfa 29, 16 > + .cfi_offset 29, -16 > + .cfi_offset 30, -8 > > ldr_this_cpu x16, irq_stack_ptr, x17 > > @@ -897,9 +916,13 @@ SYM_FUNC_START(call_on_irq_stack) > */ > mov sp, x29 > ldp x29, x30, [sp], #16 > + .cfi_restore 29 > + .cfi_restore 30 > + .cfi_def_cfa 31, 0 > scs_load_current > restore_irq x9 > ret > + .cfi_endproc > SYM_FUNC_END(call_on_irq_stack) > NOKPROBE(call_on_irq_stack) > > -- > 2.54.0.545.g6539524ca2-goog >