From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-3.9 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_EF,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED,SPF_HELO_PASS,SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from sourceware.org (server1.sourceware.org [209.132.180.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dcvr.yhbt.net (Postfix) with ESMTPS id 6D5E01F454 for ; Fri, 8 Nov 2019 14:50:23 +0000 (UTC) DomainKey-Signature: a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:date:from:to:cc:message-id:subject:references :reply-to:mime-version:content-transfer-encoding:content-type; q=dns; s=default; b=a9Y8nzPxG7CiQJAOIFpEBZIbwl2YXZB60MPiDgIxo/X TqayQjbS9OLrwOySpQZPxsbbb50kWjYhd11KfeDco3pK9SOykWIntu1F3dAgPANw znDHfJ/MTWyQlEocWRr3xNLSiL6VcY0x5ZbYfDfDa2S1XTGIysh/1zHhnGH6UvRg = DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:date:from:to:cc:message-id:subject:references :reply-to:mime-version:content-transfer-encoding:content-type; s=default; bh=vCKZpQ7yCcax35FzmCVNPcftDK8=; b=gbEjkmPURkbki2E/A 8AMbFqcHsPvPPNbh1PW1a8neARxBz1JMa37J13bEqQup1bu7yjLVKQzvEriHVgzz 610rseBQIVUYGxKS5CMXCDAYzukeYc1pGyET4XUy8XqOALzhpi7slmnSnKrSVYbf A9rpoZCXCf9Jt1FPTDHMdIMWiE= Received: (qmail 12579 invoked by alias); 8 Nov 2019 14:50:20 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Received: (qmail 12493 invoked by uid 89); 8 Nov 2019 14:50:20 -0000 Authentication-Results: sourceware.org; auth=none X-HELO: mx1.osci.io X-Gerrit-PatchSet: 1 Date: Fri, 8 Nov 2019 09:50:13 -0500 From: "Florian Weimer (Code Review)" To: libc-alpha@sourceware.org Cc: Florian Weimer Message-ID: Auto-Submitted: auto-generated X-Gerrit-MessageType: newchange Subject: [review] dlsym: Do not determine caller link map if not needed X-Gerrit-Change-Id: Ide5d9e2cc7ac25a0ffae8fb4c26def0c898efa29 X-Gerrit-Change-Number: 528 X-Gerrit-ChangeURL: X-Gerrit-Commit: f4adfc9645132874eb4b57e0c76f627db102dddd References: Reply-To: fweimer@redhat.com, fweimer@redhat.com, libc-alpha@sourceware.org MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Disposition: inline User-Agent: Gerrit/3.0.3-75-g9005159e5d Content-Type: text/plain; charset=UTF-8 Change URL: https://gnutoolchain-gerrit.osci.io/r/c/glibc/+/528 ...................................................................... dlsym: Do not determine caller link map if not needed Obtaining the link map is potentially very slow because it requires iterating over all loaded objects in the current implementation. If the caller supplied an explicit handle (i.e., not one of the RTLD_* constants), the dlsym implementation does not need the identity of the caller (except in the special cause of auditing), so this change avoids computing it in that case. Even in the minimal case (dlsym called from a main program linked with -dl), this shows a small speedup, perhaps around five percent. The performance improvement can be arbitrarily large in principle (if _dl_find_dso_for_object has to iterate over many link maps). Change-Id: Ide5d9e2cc7ac25a0ffae8fb4c26def0c898efa29 --- M elf/dl-sym.c 1 file changed, 21 insertions(+), 4 deletions(-) diff --git a/elf/dl-sym.c b/elf/dl-sym.c index 8209342..7282e09 100644 --- a/elf/dl-sym.c +++ b/elf/dl-sym.c @@ -80,6 +80,18 @@ args->flags, NULL); } +/* Return the link map containing the caller address. */ +static inline struct link_map * +find_caller_link_map (ElfW(Addr) caller) +{ + struct link_map *l = _dl_find_dso_for_object (caller); + if (l != NULL) + return l; + else + /* If the address is not recognized the call comes from the main + program (we hope). */ + return GL(dl_ns)[LM_ID_BASE]._ns_loaded; +} static void * do_sym (void *handle, const char *name, void *who, @@ -89,13 +101,13 @@ lookup_t result; ElfW(Addr) caller = (ElfW(Addr)) who; - struct link_map *l = _dl_find_dso_for_object (caller); - /* If the address is not recognized the call comes from the main - program (we hope). */ - struct link_map *match = l ? l : GL(dl_ns)[LM_ID_BASE]._ns_loaded; + /* Link map of the caller if needed. */ + struct link_map *match = NULL; if (handle == RTLD_DEFAULT) { + match = find_caller_link_map (caller); + /* Search the global scope. We have the simple case where we look up in the scope of an object which was part of the initial binary. And then the more complex part @@ -128,6 +140,8 @@ } else if (handle == RTLD_NEXT) { + match = find_caller_link_map (caller); + if (__glibc_unlikely (match == GL(dl_ns)[LM_ID_BASE]._ns_loaded)) { if (match == NULL @@ -187,6 +201,9 @@ unsigned int ndx = (ref - (ElfW(Sym) *) D_PTR (result, l_info[DT_SYMTAB])); + if (match == NULL) + match = find_caller_link_map (caller); + if ((match->l_audit_any_plt | result->l_audit_any_plt) != 0) { unsigned int altvalue = 0; -- Gerrit-Project: glibc Gerrit-Branch: master Gerrit-Change-Id: Ide5d9e2cc7ac25a0ffae8fb4c26def0c898efa29 Gerrit-Change-Number: 528 Gerrit-PatchSet: 1 Gerrit-Owner: Florian Weimer Gerrit-MessageType: newchange