From patchwork Mon Mar 2 17:32:42 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Naveen N. Rao" X-Patchwork-Id: 1247751 Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 48WS1y3VxYz9sNg for ; Tue, 3 Mar 2020 04:34:30 +1100 (AEDT) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=linux.ibm.com Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 48WS1x6WgPzDqTF for ; Tue, 3 Mar 2020 04:34:29 +1100 (AEDT) X-Original-To: linuxppc-dev@lists.ozlabs.org Delivered-To: linuxppc-dev@lists.ozlabs.org Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=linux.ibm.com (client-ip=148.163.158.5; helo=mx0a-001b2d01.pphosted.com; envelope-from=naveen.n.rao@linux.ibm.com; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=linux.ibm.com Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 48WS060m7XzDqYV for ; Tue, 3 Mar 2020 04:32:53 +1100 (AEDT) Received: from pps.filterd (m0098421.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 022HKM5J106012 for ; Mon, 2 Mar 2020 12:32:51 -0500 Received: from e06smtp04.uk.ibm.com (e06smtp04.uk.ibm.com [195.75.94.100]) by mx0a-001b2d01.pphosted.com with ESMTP id 2yfmu42xtj-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Mon, 02 Mar 2020 12:32:50 -0500 Received: from localhost by e06smtp04.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Mon, 2 Mar 2020 17:32:45 -0000 Received: from d06av22.portsmouth.uk.ibm.com (d06av22.portsmouth.uk.ibm.com [9.149.105.58]) by b06avi18878370.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 022HWiiV45220140 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 2 Mar 2020 17:32:44 GMT Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 31EB34C040; Mon, 2 Mar 2020 17:32:44 +0000 (GMT) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C1ECB4C04A; Mon, 2 Mar 2020 17:32:43 +0000 (GMT) Received: from localhost (unknown [9.199.48.41]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 2 Mar 2020 17:32:43 +0000 (GMT) Date: Mon, 02 Mar 2020 23:02:42 +0530 From: "Naveen N. Rao" Subject: eh_frame confusion To: Linux Kbuild mailing list , LKML , "linuxppc-dev@lists.ozlabs.org" , Rasmus Villemoes , Michael Ellerman References: <3b00b45f-74b5-13e3-9a98-c3d6b3bb7286@rasmusvillemoes.dk> <1583168442.ovqnxu16tp.naveen@linux.ibm.com> In-Reply-To: <1583168442.ovqnxu16tp.naveen@linux.ibm.com> MIME-Version: 1.0 User-Agent: astroid/v0.15-13-gb675b421 (https://github.com/astroidmail/astroid) X-TM-AS-GCONF: 00 x-cbid: 20030217-0016-0000-0000-000002EC5DC4 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 20030217-0017-0000-0000-0000334FA18A Message-Id: <1583169883.zo43kx69lm.naveen@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138, 18.0.572 definitions=2020-03-02_06:2020-03-02, 2020-03-02 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 suspectscore=0 spamscore=0 malwarescore=0 adultscore=0 mlxlogscore=999 bulkscore=0 mlxscore=0 impostorscore=0 clxscore=1015 phishscore=0 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2003020116 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linuxppc-dev-bounces+patchwork-incoming=ozlabs.org@lists.ozlabs.org Sender: "Linuxppc-dev" Naveen N. Rao wrote: > Rasmus Villemoes wrote: >> I'm building a ppc32 kernel, and noticed that after upgrading from gcc-7 >> to gcc-8 all object files now end up having .eh_frame section. For >> vmlinux, that's not a problem, because they all get discarded in >> arch/powerpc/kernel/vmlinux.lds.S . However, they stick around in >> modules, which doesn't seem to be useful - given that everything worked >> just fine with gcc-7, and I don't see anything in the module loader that >> handles .eh_frame. >> >> The reason I care is that my target has a rather tight rootfs budget, >> and the .eh_frame section seem to occupy 10-30% of the file size >> (obviously very depending on the particular module). >> >> Comparing the .foo.o.cmd files, I don't see change in options that might >> explain this (there's a bunch of new -Wno-*, and the -mspe=no spelling >> is apparently no longer supported in gcc-8). Both before and after, there's >> >> -fno-dwarf2-cfi-asm >> >> about which gcc's documentation says >> >> '-fno-dwarf2-cfi-asm' >> Emit DWARF unwind info as compiler generated '.eh_frame' section >> instead of using GAS '.cfi_*' directives. >> >> Looking into where that comes from got me even more confused, because >> both arm and unicore32 say >> >> # Never generate .eh_frame >> KBUILD_CFLAGS += $(call cc-option,-fno-dwarf2-cfi-asm) >> >> while the ppc32 case at hand says >> >> # FIXME: the module load should be taught about the additional relocs >> # generated by this. >> # revert to pre-gcc-4.4 behaviour of .eh_frame > > Michael opened a task to look into this recently and I had spent some > time last week on this. The original commit/discussion adding > -fno-dwarf2-cfi-asm refers to R_PPC64_REL32 relocations not being > handled by our module loader: > http://lkml.kernel.org/r/20090224065112.GA6690@bombadil.infradead.org > > However, that is now handled thanks to commit 9f751b82b491d: > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9f751b82b491d > > I did a test build and a simple module loaded fine, so I think > -fno-dwarf2-cfi-asm is not required anymore, unless Michael has seen > some breakages with it. Michael? > >> >> but prior to gcc-8, .eh_frame didn't seem to get generated anyway. >> >> Can .eh_frame sections be discarded for modules (on ppc32 at least), or >> is there some magic that makes them necessary when building with gcc-8? > > As Segher points out, it looks like we need to add > -fno-asynchronous-unwind-tables. Most other architectures seem to use > that too. Can you check if the below patch works? I am yet to test this in more detail, but would be good to know the implications for ppc32. - Naveen diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile index f35730548e42..5b5bf98b8217 100644 --- a/arch/powerpc/Makefile +++ b/arch/powerpc/Makefile @@ -239,10 +239,7 @@ KBUILD_CFLAGS += $(call cc-option,-mno-vsx) KBUILD_CFLAGS += $(call cc-option,-mno-spe) KBUILD_CFLAGS += $(call cc-option,-mspe=no) -# FIXME: the module load should be taught about the additional relocs -# generated by this. -# revert to pre-gcc-4.4 behaviour of .eh_frame -KBUILD_CFLAGS += $(call cc-option,-fno-dwarf2-cfi-asm) +KBUILD_CFLAGS += $(call cc-option,-fno-asynchronous-unwind-tables) # Never use string load/store instructions as they are # often slow when they are implemented at all diff --git a/arch/powerpc/kernel/vdso32/Makefile b/arch/powerpc/kernel/vdso32/Makefile index e147bbdc12cd..d43b0b18137c 100644 --- a/arch/powerpc/kernel/vdso32/Makefile +++ b/arch/powerpc/kernel/vdso32/Makefile @@ -25,6 +25,7 @@ KCOV_INSTRUMENT := n UBSAN_SANITIZE := n ccflags-y := -shared -fno-common -fno-builtin -nostdlib \ + -fasynchronous-unwind-tables \ -Wl,-soname=linux-vdso32.so.1 -Wl,--hash-style=both asflags-y := -D__VDSO32__ -s diff --git a/arch/powerpc/kernel/vdso64/Makefile b/arch/powerpc/kernel/vdso64/Makefile index 32ebb3522ea1..b2cbb5c49bad 100644 --- a/arch/powerpc/kernel/vdso64/Makefile +++ b/arch/powerpc/kernel/vdso64/Makefile @@ -13,6 +13,7 @@ KCOV_INSTRUMENT := n UBSAN_SANITIZE := n ccflags-y := -shared -fno-common -fno-builtin -nostdlib \ + -fasynchronous-unwind-tables \ -Wl,-soname=linux-vdso64.so.1 -Wl,--hash-style=both asflags-y := -D__VDSO64__ -s