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 B8AEF3B1BD; Tue, 18 Aug 2026 14:58:37 +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=1787065118; cv=none; b=c3roX8OS/GDs8cxnKy3aHwBT/I2eaeGtc5i1a4DEzKYJCtpC7Xl2ehELc7P5yf2Tnq+aKK7a86vgF1L6/JXUMkkkL9vVUQsUnhM90dWhKJjlm9aM0VdfW9u1+7HbEOAkmpBhRqzOCALxiQHIgWscQaEeboSZs+YZNpVDMhVjkCY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787065118; c=relaxed/simple; bh=4Vu+nZE9UEDyhecLkoSbC/EiCVJ+hdWwZn6hHPFOezk=; h=From:Subject:To:Cc:In-Reply-To:References:Content-Type:Date: Message-Id; b=LdpCn29uH7HdLCJcSc987q69u48SZoG9cBChU3ONyXB1bp3142N0BgS5PsDj5ziu4duWye6qIRgz4eoI9cZVIzxYeSNZPYxLFRpeidJ+ybm4/20OcdAgm8cp0tNsiUX+OyJKiyPkuM27FQcWHcezi1JxveKgQ6/R5+Tjqpfw+RY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Atdo0q/r; 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="Atdo0q/r" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 272861F000E9; Tue, 18 Aug 2026 14:58:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787065117; bh=5Gf5jNdflhUcRcIzTZb2ASCjaJU6U/sqJ8CISyarRio=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=Atdo0q/rbNnRPyga7OiwIJC+W4pw4d27V3L/o4alC+lEyY4oGg2rSVztgS1hhTjVr WMDsFA8w9Bdka60F4J4cgkcMu9Sz7r4eK2axsjh2XGTTES69IU8GFP1JzS2rVjhKgr 6WjJCDD3KSJWF6ejV2riqy1het8wa2AvVGwT0DEkm1s5XYxxU0L3+n2jKsOxIdHbx1 uPxUhQqcV6RiCWlCmMkDCriV+K9aGBbQ+JF8f/j69xq6DxR4FsltC26PsV8kk8DTs6 9zz0lFcmf++r+g381HFXWKAF0HHzeAjxhpR/tTA2pGB2gjZrZ8ItMrv4q9z3pO+ugT nBLnCHJ+TDl+Q== From: sashiko-bot@kernel.org Subject: Re: [RFC PATCH v1 03/25] unwind_user: Enable archs that pass RA in a register Reply-To: sashiko-reviews@lists.linux.dev To: "Jens Remus" Cc: "Alexander Gordeev" , "Vasily Gorbik" , "Heiko Carstens" , linux-s390@vger.kernel.org, "Christian Borntraeger" , linux-trace-kernel@vger.kernel.org In-Reply-To: <20260818144954.2320378-4-jremus@linux.ibm.com> References: <20260818144954.2320378-1-jremus@linux.ibm.com> <20260818144954.2320378-4-jremus@linux.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Tue, 18 Aug 2026 14:58:36 +0000 Message-Id: <20260818145837.272861F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: linux-s390@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/20260818144954.2320= 378-1-jremus@linux.ibm.com?part=3D3