From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-17.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3C8D4C4332D for ; Tue, 22 Dec 2020 14:31:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E63722313F for ; Tue, 22 Dec 2020 14:31:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727798AbgLVObZ (ORCPT ); Tue, 22 Dec 2020 09:31:25 -0500 Received: from foss.arm.com ([217.140.110.172]:36498 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726920AbgLVObX (ORCPT ); Tue, 22 Dec 2020 09:31:23 -0500 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 C62C61FB; Tue, 22 Dec 2020 06:30:37 -0800 (PST) Received: from [10.37.12.16] (unknown [10.37.12.16]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1C09E3F6CF; Tue, 22 Dec 2020 06:30:35 -0800 (PST) Subject: Re: [PATCH] arm64: do not descend to vdso directories twice To: Masahiro Yamada Cc: Catalin Marinas , Will Deacon , linux-arm-kernel , Michael Ellerman , Linux Kernel Mailing List References: <20201218024540.1102650-1-masahiroy@kernel.org> <55dc2724-cdfe-28ad-395d-707fe9bae2db@arm.com> From: Vincenzo Frascino Message-ID: <8b25f7ba-7777-e3b5-2597-2a7a6526d4c7@arm.com> Date: Tue, 22 Dec 2020 14:34:04 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/21/20 4:03 PM, Masahiro Yamada wrote: > On Mon, Dec 21, 2020 at 11:36 PM Vincenzo Frascino > wrote: >> >> Hi Masahiro, >> >> On 12/18/20 2:45 AM, Masahiro Yamada wrote: >>> arm64 descends into each vdso directory twice; first in vdso_prepare, >>> second during the ordinary build process. >>> >>> PPC mimicked it and uncovered a problem [1]. In the first descend, >>> Kbuild directly visits the vdso directories, therefore it does not >>> inherit subdir-ccflags-y from upper directories. >>> >>> This means the command line parameters may differ between the two. >>> If it happens, the offset values in the generated headers might be >>> different from real offsets of vdso.so in the kernel. >>> >>> This potential danger should be avoided. The vdso directories are >>> built in the vdso_prepare stage, so the second descend is unneeded. >>> >>> [1]: https://lore.kernel.org/linux-kbuild/CAK7LNARAkJ3_-4gX0VA2UkapbOftuzfSTVMBbgbw=HD8n7N+7w@mail.gmail.com/T/#ma10dcb961fda13f36d42d58fa6cb2da988b7e73a >>> >> >> I could not reproduce the problem you are reporting on arm64. Could you please >> provide some steps? > > > As far as I see in arm64 Makefiles, you cannot reproduce it. > So, this is a _potential_ problem. > > When somebody adds subdir-ccflags-y to arch/arm64/Kbuild or > arch/arm64/kernel/Makefile, > the real issue will suddenly come up. > > > arm64 is the first arch that implemented vdso-offsets.h > > arch maintainers tend to copy Makefiles from existing ones. > > Now PPC is the second with almost the same Makefile implementation. > > This time, powerpc hit the problem because arch/powerpc/Kbuild > has subdir-ccflags-y. > > I do not want to be bothered every time arch maintainers hit this issue. > So, I want to fix arm64 first, > then powerpc will eventually copy the correct Makefiles. > > Ok this seems a problem related to a top down approach in the ccflags propagation, which as it stands does not affect arm64, hence IMHO we should not fix what is not broken, but I do not have a strong opinion on this. > > >> In my case the vDSO library is not rebuilt as a result of the procedure reported >> in the email you linked at [1]. >> >>> Signed-off-by: Masahiro Yamada >>> --- >>> >>> arch/arm64/Makefile | 10 ++++++---- >>> arch/arm64/kernel/Makefile | 5 +++-- >>> arch/arm64/kernel/{vdso/vdso.S => vdso-wrap.S} | 0 >>> arch/arm64/kernel/vdso/Makefile | 1 - >>> arch/arm64/kernel/{vdso32/vdso.S => vdso32-wrap.S} | 0 >>> arch/arm64/kernel/vdso32/Makefile | 1 - >>> 6 files changed, 9 insertions(+), 8 deletions(-) >>> rename arch/arm64/kernel/{vdso/vdso.S => vdso-wrap.S} (100%) >>> rename arch/arm64/kernel/{vdso32/vdso.S => vdso32-wrap.S} (100%) >>> >>> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile >>> index 6a87d592bd00..f18d20a68170 100644 >>> --- a/arch/arm64/Makefile >>> +++ b/arch/arm64/Makefile >>> @@ -179,10 +179,12 @@ ifeq ($(KBUILD_EXTMOD),) >>> # this hack. >>> prepare: vdso_prepare >>> vdso_prepare: prepare0 >>> - $(Q)$(MAKE) $(build)=arch/arm64/kernel/vdso include/generated/vdso-offsets.h >>> - $(if $(CONFIG_COMPAT_VDSO),$(Q)$(MAKE) \ >>> - $(build)=arch/arm64/kernel/vdso32 \ >>> - include/generated/vdso32-offsets.h) >>> + $(Q)$(MAKE) $(build)=arch/arm64/kernel/vdso \ >>> + include/generated/vdso-offsets.h arch/arm64/kernel/vdso/vdso.so >>> +ifdef CONFIG_COMPAT_VDSO >>> + $(Q)$(MAKE) $(build)=arch/arm64/kernel/vdso32 \ >>> + include/generated/vdso32-offsets.h arch/arm64/kernel/vdso32/vdso.so >>> +endif >>> endif >> >> The reason why it is currently done in two phases (a bit hacky as per comment) >> is because vdso-offsets.h is required to be generated before compiling kernel/. >> Please refer to the comment in arch/arm64/Makefile. > > Yes, I know. > >> >> Could you explain how your change satisfies the dependency? > > vdso_prepare completes before Kbuild starts ordinary descending. > So *.so files and vdso-offsets.h exist > when Kbuild builds arch/arm64/kernel/. > > This is not immediately obvious, could you please mention it in the commit message? Nit: Could you please re-organize the code as follows in order to limit the changes (untested)? $(Q)$(MAKE) $(build)=arch/arm64/kernel/vdso include/generated/vdso-offsets.h \ arch/arm64/kernel/vdso/vdso.so $(if $(CONFIG_COMPAT_VDSO),$(Q)$(MAKE) \ $(build)=arch/arm64/kernel/vdso32 \ include/generated/vdso32-offsets.h \ arch/arm64/kernel/vdso32/vdso.so) > > > > >>> >>> define archhelp >>> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile >>> index 86364ab6f13f..42f6ad2c7eac 100644 >>> --- a/arch/arm64/kernel/Makefile >>> +++ b/arch/arm64/kernel/Makefile >>> @@ -59,9 +59,10 @@ obj-$(CONFIG_CRASH_CORE) += crash_core.o >>> obj-$(CONFIG_ARM_SDE_INTERFACE) += sdei.o >>> obj-$(CONFIG_ARM64_PTR_AUTH) += pointer_auth.o >>> obj-$(CONFIG_ARM64_MTE) += mte.o >>> +obj-y += vdso-wrap.o >>> +obj-$(CONFIG_COMPAT_VDSO) += vdso32-wrap.o >>> >>> -obj-y += vdso/ probes/ >>> -obj-$(CONFIG_COMPAT_VDSO) += vdso32/ >>> +obj-y += probes/ >>> head-y := head.o >>> extra-y += $(head-y) vmlinux.lds >>> >>> diff --git a/arch/arm64/kernel/vdso/vdso.S b/arch/arm64/kernel/vdso-wrap.S >>> similarity index 100% >>> rename from arch/arm64/kernel/vdso/vdso.S >>> rename to arch/arm64/kernel/vdso-wrap.S >>> diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile >>> index a8f8e409e2bf..85222f64f394 100644 >>> --- a/arch/arm64/kernel/vdso/Makefile >>> +++ b/arch/arm64/kernel/vdso/Makefile >>> @@ -45,7 +45,6 @@ endif >>> # Disable gcov profiling for VDSO code >>> GCOV_PROFILE := n >>> >>> -obj-y += vdso.o >>> targets += vdso.lds >>> CPPFLAGS_vdso.lds += -P -C -U$(ARCH) >>> >>> diff --git a/arch/arm64/kernel/vdso32/vdso.S b/arch/arm64/kernel/vdso32-wrap.S >>> similarity index 100% >>> rename from arch/arm64/kernel/vdso32/vdso.S >>> rename to arch/arm64/kernel/vdso32-wrap.S >>> diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile >>> index a1e0f91e6cea..789ad420f16b 100644 >>> --- a/arch/arm64/kernel/vdso32/Makefile >>> +++ b/arch/arm64/kernel/vdso32/Makefile >>> @@ -155,7 +155,6 @@ c-obj-vdso-gettimeofday := $(addprefix $(obj)/, $(c-obj-vdso-gettimeofday)) >>> asm-obj-vdso := $(addprefix $(obj)/, $(asm-obj-vdso)) >>> obj-vdso := $(c-obj-vdso) $(c-obj-vdso-gettimeofday) $(asm-obj-vdso) >>> >>> -obj-y += vdso.o >>> targets += vdso.lds >>> CPPFLAGS_vdso.lds += -P -C -U$(ARCH) >>> >>> >> >> -- >> Regards, >> Vincenzo > > > > -- > Best Regards > Masahiro Yamada > -- Regards, Vincenzo