From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id B37D5385115C for ; Tue, 6 Sep 2022 10:27:29 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org B37D5385115C Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1662460049; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=c7dNV6mVHCt2WEGseD39LNF9AaDO8YoDMmvLSQk+aDc=; b=XcYa+tmZ242q6wp2LXLidhseW1zNTXRIIfDiNrbsWQicVO4T6IXNNU4lsn8s8WZ+ybFbeR CrJtWLjUEzCfElyzaqKsQUpl/ja4SHZQ7/GPJdXm3NObhQ3zzHvyAgKxI/Xk0N1fSVpIIO i1UOIsss/PlQhWDFyap1aXyyI95uAXw= 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-199-ZsX_0eDnN1a72GDo3uAiSQ-1; Tue, 06 Sep 2022 06:27:28 -0400 X-MC-Unique: ZsX_0eDnN1a72GDo3uAiSQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 0FDAC801755 for ; Tue, 6 Sep 2022 10:27:28 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.192.109]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4FDFC9458A for ; Tue, 6 Sep 2022 10:27:27 +0000 (UTC) From: Florian Weimer To: libc-alpha@sourceware.org Subject: [PATCH v2 1/3] elf: Introduce separate _r_debug_array variable In-Reply-To: References: X-From-Line: 1fd41f326f6dc235af45df81332a6b6b8cc7b164 Mon Sep 17 00:00:00 2001 Message-Id: <1fd41f326f6dc235af45df81332a6b6b8cc7b164.1662456433.git.fweimer@redhat.com> Date: Tue, 06 Sep 2022 12:27:25 +0200 User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-11.0 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_LOW,SPF_HELO_NONE,SPF_NONE,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: 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 6b256b8388..b088f6b1ae 100644 --- a/sysdeps/generic/ldsodefs.h +++ b/sysdeps/generic/ldsodefs.h @@ -348,8 +348,6 @@ 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; -- 2.37.2