From 832ca732b8a96ff9a3e7c4abf24098bf2a59a96d Mon Sep 17 00:00:00 2001 From: "H.J. Lu" Date: Tue, 1 Nov 2022 11:36:04 -0700 Subject: x86-64: Add -z mark-plt and -z nomark-plt 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. --- ld/ld.texi | 11 +++++++++++ 1 file changed, 11 insertions(+) (limited to 'ld/ld.texi') diff --git a/ld/ld.texi b/ld/ld.texi index 24e9deb..2663f07 100644 --- a/ld/ld.texi +++ b/ld/ld.texi @@ -1475,6 +1475,17 @@ Specify that the object's filters be processed immediately at runtime. @item max-page-size=@var{value} Set the maximum memory page size supported to @var{value}. +@item mark-plt +@itemx nomark-plt +Mark PLT entries with dynamic tags, DT_X86_64_PLT, DT_X86_64_PLTSZ and +DT_X86_64_PLTENT. Since this option stores a non-zero value in the +r_addend field of R_X86_64_JUMP_SLOT relocations, the resulting +executables and shared libraries are incompatible with dynamic linkers, +such as those in older versions of glibc without the change to ignore +r_addend in R_X86_64_GLOB_DAT and R_X86_64_JUMP_SLOT relocations, which +don't ignore the r_addend field of R_X86_64_JUMP_SLOT relocations. +Supported for x86_64. + @item muldefs Allow multiple definitions. -- cgit v1.1