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Dereferences of GOT slots with lgrl or lg for global symbols are rewritten to larl to get get rid of the extra memory access. However this is invalid for: - symbols marked for absolute addressing - symbols at odd addresses (larl can handle only even addresses) Commite6213e09ed("S/390: Prevent GOT access rewrite for certain symbols") added checks for the above. But instead of checking the address of a symbol for being halfword aligned, it tries to deduce this from whether the symbol value and section the symbol is defined in are halfword aligned. The way it is done has two issues: 1. The use of bfd_section_from_elf_index to obtain the section the symbol is defined in may not return the one that remains in the output. For instance for COMDAT sections getting deduplicated the section retrieved using bfd_section_from_elf_index may not be the same as h->root.u.def.section. If COMDAT sections of same group signature have different alignment properties the wrong one may be checked. This may then lead to an erroneous rewrite of lgrl %rX, sym@GOTENT to larl %rX, sym, although the symbol in the remaining section is not properly aligned, triggering an "relocation for misaligned symbol" error at link-time. This may for instance occur when mixing C++ modules compiled with GCC and Clang, as GCC emits a 2-byte alignment and Clang a 1-byte alignment for COMDAT sections containing type information: $ cat sample.cpp #include <typeinfo> struct A {}; const std::type_info &q() { return typeid(A); } $ g++ -c sample.cpp -o sample_gcc.o $ clang++ -c sample.cpp -o sample_clang.o $ readelf -WS sample_gcc.o sample_clang.o Produces (reformatted and reduced): File Name Off Size ES Flg Lk Inf Al sample_gcc.o .rodata._ZTS1A 000080 000004 00 AG 0 0 2 sample_clang.o .rodata._ZTS1A 000058 000003 00 AG 0 0 1 2. The symbol may end up at an even address, if both the symbol value and the section defining the symbol are 1-byte aligned. While this does not trigger an error, it fails an opportunity to rewrite a GOT access. In a Linux Kernel build this causes ~15k GOT accesses using lgrl to be skipped to be rewritten to larl. Resolve both issues by simply checking whether the symbol address is halfword aligned. Do not check the symbol value nor section defining the symbol for halfword alignment. bfd/ PR ld/32969 * elf64-s390.c (elf_s390_relocate_section): Only rewrite lgrl/lg from GOT to larl if symbol address is halfword aligned. ld/testsuite/ PR ld/32969 * ld-s390/s390.exp (pr32969_64-1, pr32969_64-2): Add tests for rewrite of GOT access when COMDAT section deduplication is involved. * ld-s390/pr32969_64-1.dd: New test for rewrite of GOT access when COMDAT section deduplication is involved. * ld-s390/pr32969_64-2.dd: Likewise. * ld-s390/pr32969a.s: Likewise. * ld-s390/pr32969b.s: Likewise. * ld-s390/pr32969c.s: Likewise. Bug: https://sourceware.org/PR32969 Fixes:e6213e09ed("S/390: Prevent GOT access rewrite for certain symbols") Reported-by: Ilya Leoshkevich <iii@linux.ibm.com> Signed-off-by: Jens Remus <jremus@linux.ibm.com>
README for GNU development tools This directory contains various GNU compilers, assemblers, linkers, debuggers, etc., plus their support routines, definitions, and documentation. If you are receiving this as part of a GDB release, see the file gdb/README. If with a binutils release, see binutils/README; if with a libg++ release, see libg++/README, etc. That'll give you info about this package -- supported targets, how to use it, how to report bugs, etc. It is now possible to automatically configure and build a variety of tools with one command. To build all of the tools contained herein, run the ``configure'' script here, e.g.: ./configure make To install them (by default in /usr/local/bin, /usr/local/lib, etc), then do: make install (If the configure script can't determine your type of computer, give it the name as an argument, for instance ``./configure sun4''. You can use the script ``config.sub'' to test whether a name is recognized; if it is, config.sub translates it to a triplet specifying CPU, vendor, and OS.) If you have more than one compiler on your system, it is often best to explicitly set CC in the environment before running configure, and to also set CC when running make. For example (assuming sh/bash/ksh): CC=gcc ./configure make A similar example using csh: setenv CC gcc ./configure make Much of the code and documentation enclosed is copyright by the Free Software Foundation, Inc. See the file COPYING or COPYING.LIB in the various directories, for a description of the GNU General Public License terms under which you can copy the files. REPORTING BUGS: Again, see gdb/README, binutils/README, etc., for info on where and how to report problems.