From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 7740037E31D; Wed, 29 Apr 2026 15:26:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777476386; cv=none; b=cyBgnsaUegs84/3XpbYz9oqPP4AP9mLtd3hM4BKYjsMw9m5HBszt+Z+9xpQCLJL/qQ9vZ+oPltsT4Hr8fZRabLzps4BD2wm5OKkssJl7f0xn5XUpXJWzB40NkYd6grTTsW1cisi+qvHwxdh/YORQ8XSjAfqgrGpFd2oZH4bm1V8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777476386; c=relaxed/simple; bh=ToHBbsGGf1LD2+ZDgJuZjsnXK7XLE8KJHIPpOy6olpM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=XTKfeCRM9TegadMf6zpEwFmXQza4pj6bbfflJCnUcCQnXA0+xMfwCfXRW3qSwDPHj/CBZDptuT1lgkK1+kaJEozdHmKt8LPxW1Yhxv0rISBx4FGRX2jZK0S3rvNQm3NNIrdpop2nF1XSY5EiG95diwS5nSAKuHwF/JbT6feaE88= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=DVR5A69Y; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="DVR5A69Y" 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> Precedence: bulk X-Mailing-List: live-patching@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: <20260428183643.3796063-4-dylanbhatch@google.com> 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 >