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When functions are emitted in comdat groups, global symbols defined in duplicates of the group are treated as if they were undefined. That prevents the symbols in the discarded sections from affecting the linker's global symbol hash table or causing duplicate symbol errors. Annoyingly, when gcc emits a function to a comdat group, it does not put *all* of a function's code and data in the comdat group. Typically, constant tables, exception handling info, and debug info are emitted to normal sections outside of the group, which is a perennial source of linker problems due to the special handling needed to deal with the extra-group pieces that ought to be discarded. In the case of powerpc64-gcc, the OPD entry for a function is not put in the group. Since the function symbol is defined on the OPD entry this means we need to handle symbols in .opd specially. To see how this affects LTO in particular, consider the linker testcase PR ld/12942 (1). This testcase links an LTO object file pr12942a.o with a normal (non-LTO) object pr12942b.o. Both objects contain a definition for _Z4testv in a comdat group. On loading pr12942a.o, the linker sees a comdat group (actually linkonce section) for _Z4testv and a weak _Z4testv defined in the IR. On loading pr12942b.o, the linker sees the same comdat group, and thus discards it. However, _Z4testv is a weak symbol defined in .opd, not part of the group, so this weak symbol overrides the weak IR symbol. On (re)loading the LTO version of pr12942a.o, the linker sees another weak _Z4testv, but this one does not override the value we have from pr12942b.o. The result is a linker complaint about "`_Z4testv' ... defined in discarded section `.group' of tmpdir/pr12942b.o". * elf64-ppc.c (ppc64_elf_add_symbol_hook): If function code section for function symbols defined in .opd is discarded, let the symbol appear to be undefined. (opd_entry_value): Ensure the result section is that for the function code section in the same object as the OPD entry.
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.