832ca732b8a96ff9a3e7c4abf24098bf2a59a96d
The PLT entry in executables and shared libraries contains an indirect branch, like jmp *foo@GOTPCREL(%rip) push $index_foo jmp .PLT0 or endbr64 jmp *foo@GOTPCREL(%rip) NOP padding which is used to branch to the function, foo, defined in another object. Each R_X86_64_JUMP_SLOT relocation has a corresponding PLT entry. The dynamic tags have been added to the x86-64 psABI to mark such PLT entries: https://gitlab.com/x86-psABIs/x86-64-ABI/-/commit/6d824a52a42d173eb838b879616c1be5870b593e Add an x86-64 linker option, -z mark-plt, to mark PLT entries with #define DT_X86_64_PLT (DT_LOPROC + 0) #define DT_X86_64_PLTSZ (DT_LOPROC + 1) #define DT_X86_64_PLTENT (DT_LOPROC + 3) 1. DT_X86_64_PLT: The address of the procedure linkage table. 2. DT_X86_64_PLTSZ: The total size, in bytes, of the procedure linkage table. 3. DT_X86_64_PLTENT: The size, in bytes, of a procedure linkage table entry. and set the r_addend field of the R_X86_64_JUMP_SLOT relocation to the memory offset of the indirect branch instruction. The dynamic linker can use these tags to update the PLT section to direct branch. bfd/ * elf-linker-x86.h (elf_linker_x86_params): Add mark_plt. * elf64-x86-64.c (elf_x86_64_finish_dynamic_symbol): Set the r_addend of R_X86_64_JUMP_SLOT to the indirect branch offset in PLT entry for -z mark-plt. * elfxx-x86.c (_bfd_x86_elf_size_dynamic_sections): Add DT_X86_64_PLT, DT_X86_64_PLTSZ and DT_X86_64_PLTENT for -z mark-plt. (_bfd_x86_elf_finish_dynamic_sections): Set DT_X86_64_PLT, DT_X86_64_PLTSZ and DT_X86_64_PLTENT. (_bfd_x86_elf_get_synthetic_symtab): Ignore addend for JUMP_SLOT relocation. (_bfd_x86_elf_link_setup_gnu_properties): Set plt_indirect_branch_offset. * elfxx-x86.h (elf_x86_plt_layout): Add plt_indirect_branch_offset. binutils/ * readelf.c (get_x86_64_dynamic_type): New function. (get_dynamic_type): Call get_x86_64_dynamic_type. include/ * elf/x86-64.h (DT_X86_64_PLT): New. (DT_X86_64_PLTSZ): Likewise. (DT_X86_64_PLTENT): Likewise. ld/ * ld.texi: Document -z mark-plt and -z nomark-plt. * emulparams/elf32_x86_64.sh: Source x86-64-plt.sh. * emulparams/elf_x86_64.sh: Likewise. * emulparams/x86-64-plt.sh: New file. * testsuite/ld-x86-64/mark-plt-1.s: Likewise. * testsuite/ld-x86-64/mark-plt-1a-x32.d: Likewise. * testsuite/ld-x86-64/mark-plt-1a.d: Likewise. * testsuite/ld-x86-64/mark-plt-1b-x32.d: Likewise. * testsuite/ld-x86-64/mark-plt-1b.d: Likewise. * testsuite/ld-x86-64/mark-plt-1c-x32.d: Likewise. * testsuite/ld-x86-64/mark-plt-1c.d: Likewise. * testsuite/ld-x86-64/mark-plt-1d-x32.d: Likewise. * testsuite/ld-x86-64/mark-plt-1d.d: Likewise. * testsuite/ld-x86-64/x86-64.exp: Run -z mark-plt tests.
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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.
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