glibc/elf/tst-absolute-sym.c

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elf: Correct absolute (SHN_ABS) symbol run-time calculation [BZ #19818] Do not relocate absolute symbols by the base address. Such symbols have SHN_ABS as the section index and their value is not supposed to be affected by relocation as per the ELF gABI[1]: "SHN_ABS The symbol has an absolute value that will not change because of relocation." The reason for our non-conformance here seems to be an old SysV linker bug causing symbols like _DYNAMIC to be incorrectly emitted as absolute symbols[2]. However in a previous discussion it was pointed that this is seriously flawed by preventing the lone purpose of the existence of absolute symbols from being used[3]: "On the contrary, the only interpretation that makes sense to me is that it will not change because of relocation at link time or at load time. Absolute symbols, from the days of the earliest linking loaders, have been used to represent addresses that are outside the address space of the module (e.g., memory-mapped addresses or kernel gateway pages). They've even been used to represent true symbolic constants (e.g., system entry point numbers, sizes, version numbers). There's no other way to represent a true absolute symbol, while the meaning you seek is easily represented by giving the symbol a non-negative st_shndx value." and we ought to stop supporting our current broken interpretation. Update processing for dladdr(3) and dladdr1(3) so that SHN_ABS symbols are ignored, because under the corrected interpretation they do not represent addresses within a mapped file and therefore are not supposed to be considered. References: [1] "System V Application Binary Interface - DRAFT - 19 October 2010", The SCO Group, Section "Symbol Table", <http://www.sco.com/developers/gabi/2012-12-31/ch4.symtab.html> [2] Alan Modra, "Absolute symbols" <https://sourceware.org/ml/binutils/2012-05/msg00019.html> [3] Cary Coutant, "Re: Absolute symbols" <https://sourceware.org/ml/binutils/2012-05/msg00020.html> [BZ #19818] * sysdeps/generic/ldsodefs.h (SYMBOL_ADDRESS): Handle SHN_ABS symbols. * elf/dl-addr.c (determine_info): Ignore SHN_ABS symbols. * elf/tst-absolute-sym.c: New file. * elf/tst-absolute-sym-lib.c: New file. * elf/tst-absolute-sym-lib.lds: New file. * elf/Makefile (tests): Add `tst-absolute-sym'. (modules-names): Add `tst-absolute-sym-lib'. (LDLIBS-tst-absolute-sym-lib.so): New variable. ($(objpfx)tst-absolute-sym-lib.so): New dependency. ($(objpfx)tst-absolute-sym): New dependency.
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/* BZ #19818 absolute symbol calculation main executable.
Copyright (C) 2018-2024 Free Software Foundation, Inc.
elf: Correct absolute (SHN_ABS) symbol run-time calculation [BZ #19818] Do not relocate absolute symbols by the base address. Such symbols have SHN_ABS as the section index and their value is not supposed to be affected by relocation as per the ELF gABI[1]: "SHN_ABS The symbol has an absolute value that will not change because of relocation." The reason for our non-conformance here seems to be an old SysV linker bug causing symbols like _DYNAMIC to be incorrectly emitted as absolute symbols[2]. However in a previous discussion it was pointed that this is seriously flawed by preventing the lone purpose of the existence of absolute symbols from being used[3]: "On the contrary, the only interpretation that makes sense to me is that it will not change because of relocation at link time or at load time. Absolute symbols, from the days of the earliest linking loaders, have been used to represent addresses that are outside the address space of the module (e.g., memory-mapped addresses or kernel gateway pages). They've even been used to represent true symbolic constants (e.g., system entry point numbers, sizes, version numbers). There's no other way to represent a true absolute symbol, while the meaning you seek is easily represented by giving the symbol a non-negative st_shndx value." and we ought to stop supporting our current broken interpretation. Update processing for dladdr(3) and dladdr1(3) so that SHN_ABS symbols are ignored, because under the corrected interpretation they do not represent addresses within a mapped file and therefore are not supposed to be considered. References: [1] "System V Application Binary Interface - DRAFT - 19 October 2010", The SCO Group, Section "Symbol Table", <http://www.sco.com/developers/gabi/2012-12-31/ch4.symtab.html> [2] Alan Modra, "Absolute symbols" <https://sourceware.org/ml/binutils/2012-05/msg00019.html> [3] Cary Coutant, "Re: Absolute symbols" <https://sourceware.org/ml/binutils/2012-05/msg00020.html> [BZ #19818] * sysdeps/generic/ldsodefs.h (SYMBOL_ADDRESS): Handle SHN_ABS symbols. * elf/dl-addr.c (determine_info): Ignore SHN_ABS symbols. * elf/tst-absolute-sym.c: New file. * elf/tst-absolute-sym-lib.c: New file. * elf/tst-absolute-sym-lib.lds: New file. * elf/Makefile (tests): Add `tst-absolute-sym'. (modules-names): Add `tst-absolute-sym-lib'. (LDLIBS-tst-absolute-sym-lib.so): New variable. ($(objpfx)tst-absolute-sym-lib.so): New dependency. ($(objpfx)tst-absolute-sym): New dependency.
2018-04-04 22:09:37 +00:00
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
Prefer https to http for gnu.org and fsf.org URLs Also, change sources.redhat.com to sourceware.org. This patch was automatically generated by running the following shell script, which uses GNU sed, and which avoids modifying files imported from upstream: sed -ri ' s,(http|ftp)(://(.*\.)?(gnu|fsf|sourceware)\.org($|[^.]|\.[^a-z])),https\2,g s,(http|ftp)(://(.*\.)?)sources\.redhat\.com($|[^.]|\.[^a-z]),https\2sourceware.org\4,g ' \ $(find $(git ls-files) -prune -type f \ ! -name '*.po' \ ! -name 'ChangeLog*' \ ! -path COPYING ! -path COPYING.LIB \ ! -path manual/fdl-1.3.texi ! -path manual/lgpl-2.1.texi \ ! -path manual/texinfo.tex ! -path scripts/config.guess \ ! -path scripts/config.sub ! -path scripts/install-sh \ ! -path scripts/mkinstalldirs ! -path scripts/move-if-change \ ! -path INSTALL ! -path locale/programs/charmap-kw.h \ ! -path po/libc.pot ! -path sysdeps/gnu/errlist.c \ ! '(' -name configure \ -execdir test -f configure.ac -o -f configure.in ';' ')' \ ! '(' -name preconfigure \ -execdir test -f preconfigure.ac ';' ')' \ -print) and then by running 'make dist-prepare' to regenerate files built from the altered files, and then executing the following to cleanup: chmod a+x sysdeps/unix/sysv/linux/riscv/configure # Omit irrelevant whitespace and comment-only changes, # perhaps from a slightly-different Autoconf version. git checkout -f \ sysdeps/csky/configure \ sysdeps/hppa/configure \ sysdeps/riscv/configure \ sysdeps/unix/sysv/linux/csky/configure # Omit changes that caused a pre-commit check to fail like this: # remote: *** error: sysdeps/powerpc/powerpc64/ppc-mcount.S: trailing lines git checkout -f \ sysdeps/powerpc/powerpc64/ppc-mcount.S \ sysdeps/unix/sysv/linux/s390/s390-64/syscall.S # Omit change that caused a pre-commit check to fail like this: # remote: *** error: sysdeps/sparc/sparc64/multiarch/memcpy-ultra3.S: last line does not end in newline git checkout -f sysdeps/sparc/sparc64/multiarch/memcpy-ultra3.S
2019-09-07 05:40:42 +00:00
<https://www.gnu.org/licenses/>. */
elf: Correct absolute (SHN_ABS) symbol run-time calculation [BZ #19818] Do not relocate absolute symbols by the base address. Such symbols have SHN_ABS as the section index and their value is not supposed to be affected by relocation as per the ELF gABI[1]: "SHN_ABS The symbol has an absolute value that will not change because of relocation." The reason for our non-conformance here seems to be an old SysV linker bug causing symbols like _DYNAMIC to be incorrectly emitted as absolute symbols[2]. However in a previous discussion it was pointed that this is seriously flawed by preventing the lone purpose of the existence of absolute symbols from being used[3]: "On the contrary, the only interpretation that makes sense to me is that it will not change because of relocation at link time or at load time. Absolute symbols, from the days of the earliest linking loaders, have been used to represent addresses that are outside the address space of the module (e.g., memory-mapped addresses or kernel gateway pages). They've even been used to represent true symbolic constants (e.g., system entry point numbers, sizes, version numbers). There's no other way to represent a true absolute symbol, while the meaning you seek is easily represented by giving the symbol a non-negative st_shndx value." and we ought to stop supporting our current broken interpretation. Update processing for dladdr(3) and dladdr1(3) so that SHN_ABS symbols are ignored, because under the corrected interpretation they do not represent addresses within a mapped file and therefore are not supposed to be considered. References: [1] "System V Application Binary Interface - DRAFT - 19 October 2010", The SCO Group, Section "Symbol Table", <http://www.sco.com/developers/gabi/2012-12-31/ch4.symtab.html> [2] Alan Modra, "Absolute symbols" <https://sourceware.org/ml/binutils/2012-05/msg00019.html> [3] Cary Coutant, "Re: Absolute symbols" <https://sourceware.org/ml/binutils/2012-05/msg00020.html> [BZ #19818] * sysdeps/generic/ldsodefs.h (SYMBOL_ADDRESS): Handle SHN_ABS symbols. * elf/dl-addr.c (determine_info): Ignore SHN_ABS symbols. * elf/tst-absolute-sym.c: New file. * elf/tst-absolute-sym-lib.c: New file. * elf/tst-absolute-sym-lib.lds: New file. * elf/Makefile (tests): Add `tst-absolute-sym'. (modules-names): Add `tst-absolute-sym-lib'. (LDLIBS-tst-absolute-sym-lib.so): New variable. ($(objpfx)tst-absolute-sym-lib.so): New dependency. ($(objpfx)tst-absolute-sym): New dependency.
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#include <support/check.h>
#include <support/support.h>
#include <support/test-driver.h>
void *get_absolute (void);
static int
do_test (void)
{
void *ref = (void *) 0x55aa;
void *ptr;
ptr = get_absolute ();
if (ptr != ref)
FAIL_EXIT1 ("Got %p, expected %p\n", ptr, ref);
return 0;
}
#include <support/test-driver.c>