From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 EDEBC2877DE; Fri, 21 Aug 2026 20:02:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787342552; cv=none; b=oZPx4neW4csO7cB3mYi8xU5TdtdzyYXZPzMX9dyeOsDKYV/hKyqldLElXs3qDhnqrGMPSGO22Ar9+FXnkiOw3foIhBjBu2PihBirar5hPDrc7MVDsKh/bkY7t0JiB3g1z/kmF1/LpFmX8NYiLKazOcVB3X6C0BrnaiTLvjhIcjQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787342552; c=relaxed/simple; bh=QKmXxQH+yI2SorBvpqPMaD5v8meVsFqETCHRH4cDbBM=; h=From:Subject:To:Cc:In-Reply-To:References:Content-Type:Date: Message-Id; b=F4MXNgpxhZjXE7I/ENpPcaiJS+mvjhPWdayTniXXwo0PmGXT1ju3GQvv28UqJO2w+vpegjvkcjhetcw9j7ZThvt/IOGyoJf+tv2SRhY/fPgp/CgTA261VSqQIY6CPj7mBE3SYCMHxiIpoTJkjQXjpMReqztAssAxTrcG8VHaV5k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VNRWqiyh; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="VNRWqiyh" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4873F1F000E9; Fri, 21 Aug 2026 20:02:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787342550; bh=HFlzjHnTE4B4oQ8+AIKnE/mkWWCTV0eFLVttI7f+dZI=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=VNRWqiyhxKsrR3TKo0dIk8MpDdkWCWkL8alsizvWBNfFU6ggXElicYKcNqWMNnZFe fz4QxKv/foDHq98leefWdHSvSEpaoy7t6JbaaHaZ7iEWAtryCVREOtuaZtF1Y7e1JS 56tAhLNewVHE0hyxDPNtr9QQArZ8kpfxATWinYDSQM3PrYQp7qK9T/bOi+o0oOV8ew l5/mnBhVguoeaw0Fj/WSWADVHHrJQPnJ0nWErQpz69xz74cYiDk0Oe0Xfdh01wK+ak HjW7I+KfgLRMCNEVLEnoAC09I+rLd5pP5feXHfbRrypWu8X/BBXMJaPGkZ+r4o7t9P 3Py8zyLBbNIug== From: sashiko-bot@kernel.org Subject: Re: [RFC PATCH v2 03/24] unwind_user: Enable archs that pass RA in a register Reply-To: sashiko-reviews@lists.linux.dev To: "Jens Remus" Cc: linux-s390@vger.kernel.org, linux-trace-kernel@vger.kernel.org, "Heiko Carstens" , "Vasily Gorbik" , "Alexander Gordeev" , "Christian Borntraeger" In-Reply-To: <20260821195259.2688377-4-jremus@linux.ibm.com> References: <20260821195259.2688377-1-jremus@linux.ibm.com> <20260821195259.2688377-4-jremus@linux.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Fri, 21 Aug 2026 20:02:29 +0000 Message-Id: <20260821200230.4873F1F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: > Not all architectures/ABIs pass the return address (RA) on the stack on > function entry, like x86-64 does due to its CALL instruction pushing > the RA onto the stack. Architectures/ABIs, such as s390, also do not > require the RA to be saved on the stack in the function prologue. In > particular, the RA may never be saved to the stack at all, such as in > leaf functions. Unwinding must therefore not assume the presence of a > RA saved on stack for the topmost frame. >=20 > Treat a RA offset from CFA of zero as indication that the RA is not > saved (on the stack). For the topmost frame treat it as indication that > the RA is in the link/RA register, such as on arm64 and s390, and obtain > it from there. For non-topmost frames treat it as error, as the RA must > be saved. >=20 > Additionally allow the SP to be unchanged in the topmost frame, for > architectures where SP at function entry =3D=3D SP at call site, such as > arm64 and s390. >=20 > Note that treating a RA offset from CFA of zero as indication that > the RA is not saved on the stack additionally allows for architectures, > such as s390, where the frame pointer (FP) may be saved without the RA > being saved as well. Provided that such architectures represent this > in SFrame by encoding the "missing" RA offset using a padding RA offset > with a value of zero. >=20 > Reviewed-by: Indu Bhagat > Signed-off-by: Jens Remus Sashiko has reviewed this patch and found no issues. It looks great! --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20260821195259.2688= 377-1-jremus@linux.ibm.com?part=3D3