From patchwork Mon Apr 4 20:35:42 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Maciej W. Rozycki" X-Patchwork-Id: 11622 Received: (qmail 111219 invoked by alias); 4 Apr 2016 20:36:10 -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 Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 111200 invoked by uid 89); 4 Apr 2016 20:36:09 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.9 required=5.0 tests=AWL, BAYES_00, KAM_ASCII_DIVIDERS, RCVD_IN_DNSWL_NONE, RP_MATCHES_RCVD, SPF_PASS autolearn=ham version=3.3.2 spammy=st_type, UD:awk, UD:sym, Treat X-Spam-User: qpsmtpd, 2 recipients X-HELO: mailapp01.imgtec.com Date: Mon, 4 Apr 2016 21:35:42 +0100 From: "Maciej W. Rozycki" To: CC: Subject: [PATCH] Treat STV_HIDDEN and STV_INTERNAL symbols as STB_LOCAL Message-ID: User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 In a reference to PR ld/19908 make ld.so respect symbol export classes aka visibility and treat STV_HIDDEN and STV_INTERNAL symbols as local, preventing such symbols from preempting exported symbols. According to the ELF gABI[1] neither STV_HIDDEN nor STV_INTERNAL symbols are supposed to be present in linked binaries: "A hidden symbol contained in a relocatable object must be either removed or converted to STB_LOCAL binding by the link-editor when the relocatable object is included in an executable file or shared object." "An internal symbol contained in a relocatable object must be either removed or converted to STB_LOCAL binding by the link-editor when the relocatable object is included in an executable file or shared object." however some GNU binutils versions produce such symbols in some cases. PR ld/19908 is one and we also have this note in scripts/abilist.awk: # binutils versions up through at least 2.23 have some bugs that # caused STV_HIDDEN symbols to appear in .dynsym, though that is useless. so clearly there is linked code out there which contains such symbols which is prone to symbol table misinterpretation, and it'll be more productive if we handle this gracefully, under the Robustness Principle: "be liberal in what you accept, and conservative in what you produce", especially as this is a simple (STV_HIDDEN|STV_INTERNAL) => STB_LOCAL mapping. References: [1] "System V Application Binary Interface - DRAFT - 24 April 2001", The Santa Cruz Operation, Inc., "Symbol Table", 2016-04-04 Maciej W. Rozycki * elf/dl-addr.c (determine_info): Treat STV_HIDDEN and STV_INTERNAL symbols as local. * elf/dl-lookup.c (do_lookup_x): Likewise. * elf/dl-reloc.c (RESOLVE_MAP): Likewise. --- Hi, This has passed testing with the mips-linux-gnu target, little-endian, o32 ABI, with no regressions. Any reason why this change would not be The Right Thing To Do? NB I've noticed in many if not most places we do not respect the GNU Coding Standard WRT the `ELFW' macro and the space required before the following opening parenthesis. I decided to ignore this practice and respect the standard regardless, however I did not correct any nearby use except where the line affected had to be changed anyway. Please let me know if there is a compelling reason to do otherwise and I'll follow accordingly. Maciej glibc-elf-export-class-local.diff Index: glibc/elf/dl-addr.c =================================================================== --- glibc.orig/elf/dl-addr.c 2016-01-07 13:55:59.000000000 +0000 +++ glibc/elf/dl-addr.c 2016-03-06 06:57:12.384634956 +0000 @@ -88,6 +88,8 @@ determine_info (const ElfW(Addr) addr, s for (; (void *) symtab < (void *) symtabend; ++symtab) if ((ELFW(ST_BIND) (symtab->st_info) == STB_GLOBAL || ELFW(ST_BIND) (symtab->st_info) == STB_WEAK) + && ELFW (ST_VISIBILITY) (symtab->st_other) != STV_HIDDEN + && ELFW (ST_VISIBILITY) (symtab->st_other) != STV_INTERNAL && ELFW(ST_TYPE) (symtab->st_info) != STT_TLS && (symtab->st_shndx != SHN_UNDEF || symtab->st_value != 0) Index: glibc/elf/dl-lookup.c =================================================================== --- glibc.orig/elf/dl-lookup.c 2016-03-06 05:18:09.098564495 +0000 +++ glibc/elf/dl-lookup.c 2016-03-06 05:18:38.910397550 +0000 @@ -516,6 +516,12 @@ do_lookup_x (const char *undef_name, uin #endif } + /* Hidden and internal symbols are local, ignore them. */ + unsigned char visibility = ELFW (ST_VISIBILITY) (sym->st_other); + if (__glibc_unlikely (visibility == STV_HIDDEN + || visibility == STV_INTERNAL)) + goto skip; + switch (ELFW(ST_BIND) (sym->st_info)) { case STB_WEAK: Index: glibc/elf/dl-reloc.c =================================================================== --- glibc.orig/elf/dl-reloc.c 2016-03-05 02:29:52.306589738 +0000 +++ glibc/elf/dl-reloc.c 2016-03-06 06:57:58.050263097 +0000 @@ -233,7 +233,9 @@ _dl_relocate_object (struct link_map *l, /* This macro is used as a callback from the ELF_DYNAMIC_RELOCATE code. */ #define RESOLVE_MAP(ref, version, r_type) \ - (ELFW(ST_BIND) ((*ref)->st_info) != STB_LOCAL \ + ((ELFW (ST_BIND) ((*ref)->st_info) != STB_LOCAL \ + && ELFW (ST_VISIBILITY) ((*ref)->st_other) != STV_HIDDEN \ + && ELFW (ST_VISIBILITY) ((*ref)->st_other) != STV_INTERNAL) \ ? ((__builtin_expect ((*ref) == l->l_lookup_cache.sym, 0) \ && elf_machine_type_class (r_type) == l->l_lookup_cache.type_class) \ ? (bump_num_cache_relocations (), \