From patchwork Mon Nov 7 13:11:01 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Florian Weimer X-Patchwork-Id: 60084 Return-Path: X-Original-To: patchwork@sourceware.org Delivered-To: patchwork@sourceware.org Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id C609D385801E for ; Mon, 7 Nov 2022 13:11:31 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org C609D385801E DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1667826691; bh=pxrkTc0xFbFXCewR1T/d9KlmXF9J3EQLZI/GG5p02tI=; h=To:Subject:In-Reply-To:References:Date:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To: From; b=oJ7sb5BxB405clzkYv1fRb/qnGKIEZ2WE1C6g/xAKYRHU3AG1nuy9MM7Dqy42MFAE WW2WgLxHjhbfrkN5V9YTxbm2pBcPXXw/oyG1t4i0I8+3waC9Edpt8F73k6cMvHPycR TE/IosciLJkut88ocHJArM9X9xkGFgZbUNlBtOkk= X-Original-To: libc-alpha@sourceware.org Delivered-To: libc-alpha@sourceware.org Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id 812F33858D26 for ; Mon, 7 Nov 2022 13:11:05 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 812F33858D26 Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-340-EgoFq03jP6aKCpp9kNc-1w-1; Mon, 07 Nov 2022 08:11:03 -0500 X-MC-Unique: EgoFq03jP6aKCpp9kNc-1w-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id B0D2C833A19 for ; Mon, 7 Nov 2022 13:11:03 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.2.16.86]) by smtp.corp.redhat.com (Postfix) with ESMTPS id F3871492B12 for ; Mon, 7 Nov 2022 13:11:02 +0000 (UTC) To: libc-alpha@sourceware.org Subject: [PATCH v3 1/3] elf: Introduce separate _r_debug_array variable In-Reply-To: References: X-From-Line: 5a10aa4ba531581cfa201f8839c8fcd70ff3fccc Mon Sep 17 00:00:00 2001 Message-Id: <5a10aa4ba531581cfa201f8839c8fcd70ff3fccc.1667826585.git.fweimer@redhat.com> Date: Mon, 07 Nov 2022 14:11:01 +0100 User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com X-Spam-Status: No, score=-10.5 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2, SPF_HELO_NONE, SPF_NONE, TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Patchwork-Original-From: Florian Weimer via Libc-alpha From: Florian Weimer Reply-To: Florian Weimer Errors-To: libc-alpha-bounces+patchwork=sourceware.org@sourceware.org Sender: "Libc-alpha" It replaces the ns_debug member of the namespaces. Previously, the base namespace had an unused ns_debug member. This change also fixes a concurrency issue: Now _dl_debug_initialize only updates r_next of the previous namespace's r_debug after the new r_debug is initialized, so that only the initialized version is observed. (Client code accessing _r_debug will benefit from load dependency tracking in CPUs even without explicit barriers.) --- elf/dl-debug.c | 91 +++++++++++++++++++++----------------- sysdeps/generic/ldsodefs.h | 2 - 2 files changed, 50 insertions(+), 43 deletions(-) diff --git a/elf/dl-debug.c b/elf/dl-debug.c index 538468dc0b..66f9ad375d 100644 --- a/elf/dl-debug.c +++ b/elf/dl-debug.c @@ -30,17 +30,37 @@ extern const int verify_link_map_members[(VERIFY_MEMBER (l_addr) && VERIFY_MEMBER (l_prev)) ? 1 : -1]; +#ifdef SHARED +/* r_debug structs for secondary namespaces. The first namespace is + handled separately because its r_debug structure must overlap with + the public _r_debug symbol, so the first array element corresponds + to LM_ID_BASE + 1. See elf/dl-debug-symbols.S. */ +struct r_debug_extended _r_debug_array[DL_NNS - 1]; + +/* Return the r_debug object for the namespace NS. */ +static inline struct r_debug_extended * +get_rdebug (Lmid_t ns) +{ + if (ns == LM_ID_BASE) + return &_r_debug_extended; + else + return &_r_debug_array[ns - 1]; +} +#else /* !SHARED */ +static inline struct r_debug_extended * +get_rdebug (Lmid_t ns) +{ + return &_r_debug_extended; /* There is just one namespace. */ +} +#endif /* !SHARED */ + /* Update the `r_map' member and return the address of `struct r_debug' of the namespace NS. */ struct r_debug * _dl_debug_update (Lmid_t ns) { - struct r_debug_extended *r; - if (ns == LM_ID_BASE) - r = &_r_debug_extended; - else - r = &GL(dl_ns)[ns]._ns_debug; + struct r_debug_extended *r = get_rdebug (ns); if (r->base.r_map == NULL) atomic_store_release (&r->base.r_map, (void *) GL(dl_ns)[ns]._ns_loaded); @@ -54,34 +74,7 @@ _dl_debug_update (Lmid_t ns) struct r_debug * _dl_debug_initialize (ElfW(Addr) ldbase, Lmid_t ns) { - struct r_debug_extended *r, **pp = NULL; - - if (ns == LM_ID_BASE) - { - r = &_r_debug_extended; - /* Initialize r_version to 1. */ - if (_r_debug_extended.base.r_version == 0) - _r_debug_extended.base.r_version = 1; - } - else if (DL_NNS > 1) - { - r = &GL(dl_ns)[ns]._ns_debug; - if (r->base.r_brk == 0) - { - /* Add the new namespace to the linked list. After a namespace - is initialized, r_brk becomes non-zero. A namespace becomes - empty (r_map == NULL) when it is unused. But it is never - removed from the linked list. */ - struct r_debug_extended *p; - for (pp = &_r_debug_extended.r_next; - (p = *pp) != NULL; - pp = &p->r_next) - ; - - r->base.r_version = 2; - } - } - + struct r_debug_extended *r = get_rdebug (ns); if (r->base.r_brk == 0) { /* Tell the debugger where to find the map of loaded objects. @@ -89,20 +82,36 @@ _dl_debug_initialize (ElfW(Addr) ldbase, Lmid_t ns) only once. */ r->base.r_ldbase = ldbase ?: _r_debug_extended.base.r_ldbase; r->base.r_brk = (ElfW(Addr)) &_dl_debug_state; - r->r_next = NULL; + +#ifdef SHARED + /* Add the new namespace to the linked list. This assumes that + namespaces are allocated in increasing order. After a + namespace is initialized, r_brk becomes non-zero. A + namespace becomes empty (r_map == NULL) when it is unused. + But it is never removed from the linked list. */ + + if (ns != LM_ID_BASE) + { + r->base.r_version = 2; + if (ns - 1 == LM_ID_BASE) + { + atomic_store_release (&_r_debug_extended.r_next, r); + /* Now there are multiple namespaces. */ + atomic_store_release (&_r_debug_extended.base.r_version, 2); + } + else + /* Update r_debug_extended of the previous namespace. */ + atomic_store_release (&_r_debug_array[ns - 2].r_next, r); + } + else +#endif /* SHARED */ + r->base.r_version = 1; } if (r->base.r_map == NULL) atomic_store_release (&r->base.r_map, (void *) GL(dl_ns)[ns]._ns_loaded); - if (pp != NULL) - { - atomic_store_release (pp, r); - /* Bump r_version to 2 for the new namespace. */ - atomic_store_release (&_r_debug_extended.base.r_version, 2); - } - return &r->base; } diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h index 9dae72b1ed..f668a954d3 100644 --- a/sysdeps/generic/ldsodefs.h +++ b/sysdeps/generic/ldsodefs.h @@ -351,8 +351,6 @@ struct rtld_global size_t n_elements; void (*free) (void *); } _ns_unique_sym_table; - /* Keep track of changes to each namespace' list. */ - struct r_debug_extended _ns_debug; } _dl_ns[DL_NNS]; /* One higher than index of last used namespace. */ EXTERN size_t _dl_nns;