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author | Maciej W. Rozycki <macro@mips.com> | 2018-04-04 23:09:37 +0100 |
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committer | Maciej W. Rozycki <macro@mips.com> | 2018-04-04 23:09:37 +0100 |
commit | e7feec374c635b6a29d65c39ae5e1855528fed39 (patch) | |
tree | 66022e087f86c5dde38a9e6b565565d4e909f60c /elf/tst-audit11mod2.map | |
parent | 10a446ddcc1100d6d76c6aa0c6d4775209388152 (diff) | |
download | glibc-e7feec374c635b6a29d65c39ae5e1855528fed39.tar.gz glibc-e7feec374c635b6a29d65c39ae5e1855528fed39.tar.xz glibc-e7feec374c635b6a29d65c39ae5e1855528fed39.zip |
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.
Diffstat (limited to 'elf/tst-audit11mod2.map')
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