x86-64: Add -z mark-plt and -z nomark-plt
authorH.J. Lu <hjl.tools@gmail.com>
Tue, 1 Nov 2022 18:36:04 +0000 (11:36 -0700)
committerH.J. Lu <hjl.tools@gmail.com>
Fri, 29 Sep 2023 14:58:53 +0000 (07:58 -0700)
commit832ca732b8a96ff9a3e7c4abf24098bf2a59a96d
tree5ee140bdc26d1d37696b865c80becee32ecde8c6
parenta78c3c9717e8fa98b11482f948e71c6d1d9d0e44
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.
20 files changed:
bfd/elf-linker-x86.h
bfd/elf64-x86-64.c
bfd/elfxx-x86.c
bfd/elfxx-x86.h
binutils/readelf.c
include/elf/x86-64.h
ld/emulparams/elf32_x86_64.sh
ld/emulparams/elf_x86_64.sh
ld/emulparams/x86-64-plt.sh [new file with mode: 0644]
ld/ld.texi
ld/testsuite/ld-x86-64/mark-plt-1.s [new file with mode: 0644]
ld/testsuite/ld-x86-64/mark-plt-1a-x32.d [new file with mode: 0644]
ld/testsuite/ld-x86-64/mark-plt-1a.d [new file with mode: 0644]
ld/testsuite/ld-x86-64/mark-plt-1b-x32.d [new file with mode: 0644]
ld/testsuite/ld-x86-64/mark-plt-1b.d [new file with mode: 0644]
ld/testsuite/ld-x86-64/mark-plt-1c-x32.d [new file with mode: 0644]
ld/testsuite/ld-x86-64/mark-plt-1c.d [new file with mode: 0644]
ld/testsuite/ld-x86-64/mark-plt-1d-x32.d [new file with mode: 0644]
ld/testsuite/ld-x86-64/mark-plt-1d.d [new file with mode: 0644]
ld/testsuite/ld-x86-64/x86-64.exp