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ELFv2 functions with localentry:0 are those with a single entry point, ie. global entry == local entry, and that have no requirement on r2 or r12, and guarantee r2 is unchanged on return. Such an external function can be called via the PLT without saving r2 or restoring it on return, avoiding a common load-hit-store for small functions. The optimization is attractive. The TOC pointer load-hit-store is a major reason why calls to small functions that need no register saves, or with shrink-wrap, no register saves on a fast path, are slow on powerpc64le. To be safe, this optimization needs ld.so support to check that the run-time matches link-time function implementation. If a function in a shared library with st_other localentry non-zero is called without saving and restoring r2, r2 will be trashed on return, leading to segfaults. For that reason the optimization does not happen for weak functions since a weak definition is a fairly solid hint that the function will likely be overridden. I'm also not enabling the optimization by default unless glibc-2.26 is detected, which should have the ld.so checks implemented. bfd/ * elf64-ppc.c (struct ppc_link_hash_table): Add has_plt_localentry0. (ppc64_elf_merge_symbol_attribute): Merge localentry bits from dynamic objects. (is_elfv2_localentry0): New function. (ppc64_elf_tls_setup): Default params->plt_localentry0. (plt_stub_size): Adjust size for tls_get_addr_opt stub. (build_tls_get_addr_stub): Use a simpler stub when r2 is not saved. (ppc64_elf_size_stubs): Leave stub_type as ppc_stub_plt_call for optimized localentry:0 stubs. (ppc64_elf_build_stubs): Save r2 in ELFv2 __glink_PLTresolve. (ppc64_elf_relocate_section): Leave nop unchanged for optimized localentry:0 stubs. (ppc64_elf_finish_dynamic_sections): Set PPC64_OPT_LOCALENTRY in DT_PPC64_OPT. * elf64-ppc.h (struct ppc64_elf_params): Add plt_localentry0. include/ * elf/ppc64.h (PPC64_OPT_LOCALENTRY): Define. ld/ * emultempl/ppc64elf.em (params): Init plt_localentry0 field. (enum ppc64_opt): New, replacing OPTION_* defines. Add OPTION_PLT_LOCALENTRY, and OPTION_NO_PLT_LOCALENTRY. (PARSE_AND_LIST_*): Support --plt-localentry and --no-plt-localentry. * testsuite/ld-powerpc/elfv2so.d: Update. * testsuite/ld-powerpc/powerpc.exp (TLS opt 5): Use --no-plt-localentry. * testsuite/ld-powerpc/tlsopt5.d: Update.
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.