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 943BE19F40B; Fri, 7 Aug 2026 10:54:27 +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=1786100068; cv=none; b=tTBHTWDJc04cZAssXvHLgx+w2hKOkPo92AxvL8gt0ImyXEm6HgLle6RXpy9zM+Gf43jhrvC6Y554xzB33pDJ/fTgvJ4ziwsyVV0hNmGYTm0XnfNI7UvHxZi7WYmm7t9e+pBqO2ggAeusY27AjUXNvCTghaujUb0Llhx9zYUm9Ho= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786100068; c=relaxed/simple; bh=dp9uSnLA1V71JIR7gUQ9tH62eSixAWcWfRQL2i9FZhM=; h=From:Subject:To:Cc:In-Reply-To:References:Content-Type:Date: Message-Id; b=Gp7BLpLrKQ5h/9PjtZAHZENQnWnffuwHPEEngoqH2/i8Lu26iZMDvz/4IOrqJlmmi68mj7+b1QI+dYsqoOHFki/DBUt1eO2veypCdHf1rBR6n7PV1uIMKvTq+77Xg+OZLu858pmV6zS6bNxPuh08gucv5mi/LJ7xLxdRUm/UYn4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=OnOWFxv1; 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="OnOWFxv1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D37191F000E9; Fri, 7 Aug 2026 10:54:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786100067; bh=jrC3JRKanPJQ2wb2blb79sDc8qkVGp+fcRspEGIOK6c=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=OnOWFxv1tMcYq+irZP3jBEPg3YO999d9Ecc7XDTcmDBhtBX2XYcoz5KHV7VMMEiSe 4Iwose+YTMOxgqR05ENRSCMX3okc7zXWsPceA3moW2qAyKECDJ+klxQ83zP1JqbP6s dnACrUd/IKFDPOcHJAXSI0h/KRwjHQfcAWOLcxYffVLqP3YuaL2j4uSougiedt1oqT AI7YLes5NQNkMXwiji/3KXafYb67DGv5YpFwlsxTqraOouvkqSg8VqVrUxFYdORIjF CS17bjcmTXXIRUuwqpR9l+2ccYgZXg5aol8IUzKkE7cNqhwYV6V46afF9wSjUlg0TF HENjAw2NgLafg== From: sashiko-bot@kernel.org Subject: Re: [PATCH] perf evsel: Improve frame pointer unwinding warning for s390 Reply-To: sashiko-reviews@lists.linux.dev To: "Jens Remus" Cc: "Heiko Carstens" , "Vasily Gorbik" , linux-perf-users@vger.kernel.org, linux-s390@vger.kernel.org, "Alexander Gordeev" In-Reply-To: <20260807104913.1784943-1-jremus@linux.ibm.com> References: <20260807104913.1784943-1-jremus@linux.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Fri, 07 Aug 2026 10:54:26 +0000 Message-Id: <20260807105426.D37191F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: > On s390 the kernel uses s390 back chain instead of frame pointers for > stack tracing of user space since v6.7 commit aa44433ac4ee ("s390: add > USER_STACKTRACE support"). This is because frame pointers on s390 > cannot be used for stack tracing. [1] >=20 > This requires user space to maintain a s390 back chain. For instance > user space to be built with compiler option '-mbackchain' (instead of > '-fno-omit-frame-pointer' used on other architectures, which should > better not be used on s390 [1]). >=20 > Only few distributions and users built user space with '-mbackchain'. > Therefore '--call-graph fp' may not produce the expected results. >=20 > Commit ca76fb67ebdd ("perf evlist: Improve default event for s390") > added a warning for s390 that wrongly claimed that "Framepointer > unwinding lacks kernel support". Change the warning to hint at using > '--call-graph dwarf' if user space does not maintain a s390 back chain. >=20 > Note that '--call-graph fp' may also be useful for other applications, > such as OpenJDK maintaining a s390 back chain (does not require JVM > option '-XX:+PreserveFramePointer' on s390): >=20 > $ perf record --call-graph fp ... -- \ > java -XX:+UnlockDiagnosticVMOptions -XX:+DumpPerfMapAtExit ... >=20 > [1]: s390: Stack tracing using Frame Pointer, Back Chain, and SFrame, > https://conf.gnu-tools-cauldron.org/opo25/talk/Y3CVHY/ >=20 > Fixes: ca76fb67ebdd ("perf evlist: Improve default event for s390") > 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/20260807104913.1784= 943-1-jremus@linux.ibm.com?part=3D1