From patchwork Mon Jun 18 18:07:03 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Maciej W. Rozycki" X-Patchwork-Id: 27909 Received: (qmail 100260 invoked by alias); 18 Jun 2018 18:08:11 -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 100244 invoked by uid 89); 18 Jun 2018 18:08:10 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-9.4 required=5.0 tests=AWL, BAYES_00, GIT_PATCH_2, GIT_PATCH_3, KAM_ASCII_DIVIDERS, KAM_SHORT, KAM_STOCKGEN, SPF_PASS autolearn=ham version=3.3.2 spammy=dating, Got, 00000000 X-HELO: 9pmail.ess.barracuda.com Date: Mon, 18 Jun 2018 19:07:03 +0100 From: "Maciej W. Rozycki" To: CC: Alan Modra Subject: [PATCH 1/2] elf: Accept absolute (SHN_ABS) symbols whose value is zero [BZ #23307] In-Reply-To: Message-ID: References: User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 X-ClientProxiedBy: mipsdag02.mipstec.com (10.20.40.47) To mipsdag02.mipstec.com (10.20.40.47) X-BESS-ID: 1529345280-637138-14484-104370-1 X-BESS-VER: 2018.7-r1806151722 X-BESS-Apparent-Source-IP: 12.201.5.32 X-BESS-Envelope-From: Maciej.Rozycki@mips.com X-BESS-Outbound-Spam-Score: 0.00 X-BESS-Outbound-Spam-Status: SCORE=0.00 using account:ESS59374 scores of KILL_LEVEL=7.0 tests=BSF_BESS_OUTBOUND X-BESS-Orig-Rcpt: libc-alpha@sourceware.org,amodra@gmail.com X-BESS-BRTS-Status: 1 We have this condition in `check_match' (in elf/dl-lookup.c): if (__glibc_unlikely ((sym->st_value == 0 /* No value. */ && stt != STT_TLS) || ELF_MACHINE_SYM_NO_MATCH (sym) || (type_class & (sym->st_shndx == SHN_UNDEF)))) return NULL; which causes all !STT_TLS symbols whose value is zero to be silently ignored in lookup. This may make sense for regular symbols, however not for absolute (SHN_ABS) ones, where zero is like any value, there's no special meaning attached to it. Consequently legitimate programs fail, for example taking the `elf/tst-absolute-sym' test case, substituting 0 for 0x55aa in `elf/tst-absolute-sym-lib.lds' and then trying to run the resulting program we get this: $ .../elf/tst-absolute-sym .../elf/tst-absolute-sym: symbol lookup error: .../elf/tst-absolute-sym-lib.so: undefined symbol: absolute $ even though the symbol clearly is there: $ readelf --dyn-syms .../elf/tst-absolute-sym-lib.so | grep '\babsolute\b' 7: 00000000 0 NOTYPE GLOBAL DEFAULT ABS absolute $ The check for the zero value has been there since forever or commit d66e34cd4234/08162fa88891 ("Implemented runtime dynamic linker to support ELF shared libraries.") dating back to May 2nd 1995, and the problem triggers regardless of commit e7feec374c63 ("elf: Correct absolute (SHN_ABS) symbol run-time calculation [BZ #19818]") being present or not. Fix the issue then, by permitting `sym->st_value' to be 0 for SHN_ABS symbols in lookup. [BZ #23307] * elf/dl-lookup.c (check_match): Do not reject a symbol whose `st_value' is 0 if `st_shndx' is SHN_ABS. * elf/tst-absolute-zero.c: New file. * elf/tst-absolute-zero-lib.c: New file. * elf/tst-absolute-zero-lib.lds: New file. * elf/Makefile (tests): Add `tst-absolute-zero'. (modules-names): Add `tst-absolute-zero-lib'. (LDLIBS-tst-absolute-zero-lib.so): New variable. ($(objpfx)tst-absolute-zero-lib.so): New dependency. ($(objpfx)tst-absolute-zero: New dependency. --- Hi, This has been regression-tested successfully with the `mips-linux-gnu' target and the o32 ABI, big endianness. The new test case fails with an "undefined symbol" message where the fix included here to `check_match' has been removed whether commit e7feec374c63 ("elf: Correct absolute (SHN_ABS) symbol run-time calculation [BZ #19818]") is also present or not, and it passes with the fix applied. OK to apply? Maciej --- elf/Makefile | 8 ++++++-- elf/dl-lookup.c | 1 + elf/tst-absolute-zero-lib.c | 25 +++++++++++++++++++++++++ elf/tst-absolute-zero-lib.lds | 1 + elf/tst-absolute-zero.c | 38 ++++++++++++++++++++++++++++++++++++++ 5 files changed, 71 insertions(+), 2 deletions(-) glibc-elf-shn-abs-zero.diff Index: glibc/elf/Makefile =================================================================== --- glibc.orig/elf/Makefile 2018-06-18 18:12:19.911942887 +0100 +++ glibc/elf/Makefile 2018-06-18 18:12:40.092259983 +0100 @@ -186,7 +186,7 @@ tests += restest1 preloadtest loadfail m tst-tlsalign tst-tlsalign-extern tst-nodelete-opened \ tst-nodelete2 tst-audit11 tst-audit12 tst-dlsym-error tst-noload \ tst-latepthread tst-tls-manydynamic tst-nodelete-dlclose \ - tst-debug1 tst-main1 tst-absolute-sym tst-big-note + tst-debug1 tst-main1 tst-absolute-sym tst-absolute-zero tst-big-note # reldep9 tests-internal += loadtest unload unload2 circleload1 \ neededtest neededtest2 neededtest3 neededtest4 \ @@ -273,7 +273,7 @@ modules-names = testobj1 testobj2 testob tst-latepthreadmod $(tst-tls-many-dynamic-modules) \ tst-nodelete-dlclose-dso tst-nodelete-dlclose-plugin \ tst-main1mod tst-libc_dlvsym-dso tst-absolute-sym-lib \ - tst-big-note-lib + tst-absolute-zero-lib tst-big-note-lib ifeq (yes,$(have-mtls-dialect-gnu2)) tests += tst-gnu2-tls1 @@ -1456,6 +1456,10 @@ LDLIBS-tst-absolute-sym-lib.so = tst-abs $(objpfx)tst-absolute-sym-lib.so: $(LDLIBS-tst-absolute-sym-lib.so) $(objpfx)tst-absolute-sym: $(objpfx)tst-absolute-sym-lib.so +LDLIBS-tst-absolute-zero-lib.so = tst-absolute-zero-lib.lds +$(objpfx)tst-absolute-zero-lib.so: $(LDLIBS-tst-absolute-zero-lib.so) +$(objpfx)tst-absolute-zero: $(objpfx)tst-absolute-zero-lib.so + # Both the main program and the DSO for tst-libc_dlvsym need to link # against libdl. $(objpfx)tst-libc_dlvsym: $(libdl) Index: glibc/elf/dl-lookup.c =================================================================== --- glibc.orig/elf/dl-lookup.c 2018-06-17 09:06:30.202407070 +0100 +++ glibc/elf/dl-lookup.c 2018-06-18 18:12:36.138114433 +0100 @@ -76,6 +76,7 @@ check_match (const char *const undef_nam unsigned int stt = ELFW(ST_TYPE) (sym->st_info); assert (ELF_RTYPE_CLASS_PLT == 1); if (__glibc_unlikely ((sym->st_value == 0 /* No value. */ + && sym->st_shndx != SHN_ABS && stt != STT_TLS) || ELF_MACHINE_SYM_NO_MATCH (sym) || (type_class & (sym->st_shndx == SHN_UNDEF)))) Index: glibc/elf/tst-absolute-zero-lib.c =================================================================== --- /dev/null 1970-01-01 00:00:00.000000000 +0000 +++ glibc/elf/tst-absolute-zero-lib.c 2018-06-18 18:12:40.102324540 +0100 @@ -0,0 +1,25 @@ +/* BZ #xxxxx absolute zero symbol calculation shared module. + Copyright (C) 2018 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +extern char absolute; + +void * +get_absolute (void) +{ + return &absolute; +} Index: glibc/elf/tst-absolute-zero-lib.lds =================================================================== --- /dev/null 1970-01-01 00:00:00.000000000 +0000 +++ glibc/elf/tst-absolute-zero-lib.lds 2018-06-18 18:12:40.129495568 +0100 @@ -0,0 +1 @@ +"absolute" = 0; Index: glibc/elf/tst-absolute-zero.c =================================================================== --- /dev/null 1970-01-01 00:00:00.000000000 +0000 +++ glibc/elf/tst-absolute-zero.c 2018-06-18 18:12:40.147611912 +0100 @@ -0,0 +1,38 @@ +/* BZ #xxxxx absolute zero symbol calculation main executable. + Copyright (C) 2018 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +#include +#include +#include + +void *get_absolute (void); + +static int +do_test (void) +{ + void *ref = (void *) 0; + void *ptr; + + ptr = get_absolute (); + if (ptr != ref) + FAIL_EXIT1 ("Got %p, expected %p\n", ptr, ref); + + return 0; +} + +#include