From patchwork Tue Mar 29 20:44:39 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nicolas Pitre X-Patchwork-Id: 64625 Delivered-To: patch@linaro.org Received: by 10.112.199.169 with SMTP id jl9csp2235572lbc; Tue, 29 Mar 2016 13:46:14 -0700 (PDT) X-Received: by 10.66.152.231 with SMTP id vb7mr6732169pab.132.1459284374082; Tue, 29 Mar 2016 13:46:14 -0700 (PDT) Return-Path: Received: from vger.kernel.org (vger.kernel.org. [209.132.180.67]) by mx.google.com with ESMTP id sf6si762931pac.76.2016.03.29.13.46.13; Tue, 29 Mar 2016 13:46:14 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE dis=NONE) header.from=linaro.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932456AbcC2UqK (ORCPT + 29 others); Tue, 29 Mar 2016 16:46:10 -0400 Received: from alt22.smtp-out.videotron.ca ([70.80.0.73]:35095 "EHLO alt22.smtp-out.videotron.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754525AbcC2UpM (ORCPT ); Tue, 29 Mar 2016 16:45:12 -0400 Received: from yoda.home ([96.23.157.65]) by Videotron with SMTP id l0VhaWgu2de0Fl0ViasB0X; Tue, 29 Mar 2016 16:45:10 -0400 X-Authority-Analysis: v=2.1 cv=K+CCZ3iI c=1 sm=1 tr=0 a=keA3yYpnlypCNW5BNWqu+w==:117 a=keA3yYpnlypCNW5BNWqu+w==:17 a=L9H7d07YOLsA:10 a=9cW_t1CCXrUA:10 a=s5jvgZ67dGcA:10 a=7OsogOcEt9IA:10 a=KKAkSRfTAAAA:8 a=Tty9oNO6AAAA:8 a=ZSXhne8G9MgRMkPpJisA:9 Received: from xanadu.home (xanadu.home [192.168.2.2]) by yoda.home (Postfix) with ESMTP id 5AF922DA05AA; Tue, 29 Mar 2016 16:45:08 -0400 (EDT) From: Nicolas Pitre To: Michal Marek Cc: linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v7 5/8] kbuild: add fine grained build dependencies for exported symbols Date: Tue, 29 Mar 2016 16:44:39 -0400 Message-Id: <1459284282-6676-6-git-send-email-nicolas.pitre@linaro.org> X-Mailer: git-send-email 2.5.5 In-Reply-To: <1459284282-6676-1-git-send-email-nicolas.pitre@linaro.org> References: <1459284282-6676-1-git-send-email-nicolas.pitre@linaro.org> X-CMAE-Envelope: MS4wfMB8Rb0auSt0RgZILxywFhP3/8zNyk7vZMYTwSwxpOSYj8VXktOeR7PJlwU60HSDJLTDg0IGoLrgph2GfaRTdoyujcV9sV+mn/KDJxEJ4O8A+fpuko/M QR2MYcRSFrGLypMNvS6gdLopEUoyvV9sVqGG2OZxD+EHCzbnW4Jea2QgnqBArthoh3DsIe2fHymshOHgAwWxjZHpLRbQOXlTbT7gOEmS1mQN1kWk0fLEsbHK NsY8kmmpC15cXj82KT0g2w== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Like with kconfig options, we now have the ability to compile in and out individual EXPORT_SYMBOL() declarations based on the content of include/generated/autoksyms.h. However we don't want the entire world to be rebuilt whenever that file is touched. Let's apply the same build dependency trick used for CONFIG_* symbols where the time stamp of empty files whose paths matching those symbols is used to trigger fine grained rebuilds. In our case the key is the symbol name passed to EXPORT_SYMBOL(). However, unlike config options, we cannot just use fixdep to parse the source code for EXPORT_SYMBOL(ksym) because several variants exist and parsing them all in a separate tool, and keeping it in synch, is not trivially maintainable. Furthermore, there are variants such as EXPORT_SYMBOL_GPL(pci_user_read_config_##size); that are instanciated via a macro for which we can't easily determine the actual exported symbol name(s) short of actually running the preprocessor on them. Storing the symbol name string in a special ELF section doesn't work for targets that output assembly or preprocessed source. So the best way is really to leverage the preprocessor by having it output actual symbol names anchored by a special sequence that can be easily filtered out. Then the list of symbols is simply fed to fixdep to be merged with the other dependencies. That implies the preprocessor is executed twice for each source file. A previous attempt relied on a warning pragma for each EXPORT_SYMBOL() instance that was filtered apart from stderr by the build system with a sed script during the actual compilation pass. Unfortunately the preprocessor/compiler diagnostic output isn't stable between versions and this solution, although more efficient, was deemed too fragile. Because of the lowercasing performed by fixdep, there might be name collisions triggering spurious rebuilds for similar symbols. But this shouldn't be a big issue in practice. (This is the case for CONFIG_* symbols and I didn't want to be different here, whatever the original reason for doing so.) To avoid needless build overhead, the exported symbol name gathering is performed only when CONFIG_TRIM_UNUSED_KSYMS is selected. Signed-off-by: Nicolas Pitre Acked-by: Rusty Russell --- include/linux/export.h | 13 ++++++++++++- scripts/Kbuild.include | 27 +++++++++++++++++++++++++++ scripts/basic/fixdep.c | 1 + 3 files changed, 40 insertions(+), 1 deletion(-) -- 2.5.5 diff --git a/include/linux/export.h b/include/linux/export.h index 77afdb2a25..2f9ccbe6a6 100644 --- a/include/linux/export.h +++ b/include/linux/export.h @@ -65,7 +65,18 @@ extern struct module __this_module; __attribute__((section("___ksymtab" sec "+" #sym), unused)) \ = { (unsigned long)&sym, __kstrtab_##sym } -#ifdef CONFIG_TRIM_UNUSED_KSYMS +#if defined(__KSYM_DEPS__) + +/* + * For fine grained build dependencies, we want to tell the build system + * about each possible exported symbol even if they're not actually exported. + * We use a string pattern that is unlikely to be valid code that the build + * system filters out from the preprocessor output (see ksym_dep_filter + * in scripts/Kbuild.include). + */ +#define __EXPORT_SYMBOL(sym, sec) === __KSYM_##sym === + +#elif defined(CONFIG_TRIM_UNUSED_KSYMS) #include #include diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include index 80ca538bfb..a09927e027 100644 --- a/scripts/Kbuild.include +++ b/scripts/Kbuild.include @@ -258,12 +258,39 @@ if_changed_dep = $(if $(strip $(any-prereq) $(arg-check) ), \ @set -e; \ $(cmd_and_fixdep), @:) +ifndef CONFIG_TRIM_UNUSED_KSYMS + cmd_and_fixdep = \ $(echo-cmd) $(cmd_$(1)); \ scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(dot-target).tmp;\ rm -f $(depfile); \ mv -f $(dot-target).tmp $(dot-target).cmd; +else + +# Filter out exported kernel symbol names from the preprocessor output. +# See also __KSYM_DEPS__ in include/linux/export.h. +# We disable the depfile generation here, so as not to overwrite the existing +# depfile while fixdep is parsing it. +flags_nodeps = $(filter-out -Wp$(comma)-M%, $($(1))) +ksym_dep_filter = \ + case "$(1)" in \ + cc_*_c) $(CPP) $(call flags_nodeps,c_flags) -D__KSYM_DEPS__ $< ;; \ + as_*_S) $(CPP) $(call flags_nodeps,a_flags) -D__KSYM_DEPS__ $< ;; \ + boot*|build*|*cpp_lds_S|dtc|host*|vdso*) : ;; \ + *) echo "Don't know how to preprocess $(1)" >&2; false ;; \ + esac | sed -rn 's/^.*=== __KSYM_(.*) ===.*$$/KSYM_\1/p' + +cmd_and_fixdep = \ + $(echo-cmd) $(cmd_$(1)); \ + $(ksym_dep_filter) | \ + scripts/basic/fixdep -e $(depfile) $@ '$(make-cmd)' \ + > $(dot-target).tmp; \ + rm -f $(depfile); \ + mv -f $(dot-target).tmp $(dot-target).cmd; + +endif + # Usage: $(call if_changed_rule,foo) # Will check if $(cmd_foo) or any of the prerequisites changed, # and if so will execute $(rule_foo). diff --git a/scripts/basic/fixdep.c b/scripts/basic/fixdep.c index 7e90a1f7de..746ec1ece6 100644 --- a/scripts/basic/fixdep.c +++ b/scripts/basic/fixdep.c @@ -358,6 +358,7 @@ static void parse_dep_file(void *map, size_t len) /* Ignore certain dependencies */ if (strrcmp(s, "include/generated/autoconf.h") && + strrcmp(s, "include/generated/autoksyms.h") && strrcmp(s, "arch/um/include/uml-config.h") && strrcmp(s, "include/linux/kconfig.h") && strrcmp(s, ".ver")) {