[PATCH 0/9] x86-64: Stack protector and percpu improvements

[Brian Gerst]

Currently, x86-64 uses an unusual per-cpu layout, where the percpu section
is linked at absolute address 0.  The reason behind this is that older GCC
versions placed the stack protector (if enabled) at a fixed offset from the
GS segment base.  Since the GS segement is also used for percpu variables,
this forced the current layout.

GCC since version 8.1 supports a configurable location for the stack
protector value, which allows removal of the restriction on how the percpu
section is linked.  This allows the percpu section to be linked
normally, like most other architectures.  In turn, this allows removal
of code that was needed to support the zero-based percpu section.

P.S.:  I posted this series back in 2021, and at the time it appeared that
GCC 8.1 was too recent (released May 2, 2018) to be a requirement to keep
stack protector support.  Two years later, support for the new compiler
options should be much more widespread.

Brian Gerst (9):
  x86/stackprotector/32: Remove stack protector test script
  x86/boot: Disable stack protector for early boot code
  x86/stackprotector/64: Convert stack protector to normal percpu
    variable
  x86/percpu/64: Remove fixed_percpu_data
  x86/percpu/64: Use relative percpu offsets
  x86/boot/64: Remove inverse relocations
  x86/percpu/64: Remove INIT_PER_CPU macros
  percpu: Remove PER_CPU_FIRST_SECTION
  kallsyms: Remove KALLSYMS_ABSOLUTE_PERCPU

 arch/x86/Kconfig                          |   7 +-
 arch/x86/Makefile                         |  19 +--
 arch/x86/boot/compressed/misc.c           |  14 +--
 arch/x86/entry/entry_64.S                 |   2 +-
 arch/x86/include/asm/percpu.h             |  22 ----
 arch/x86/include/asm/processor.h          |  28 +----
 arch/x86/include/asm/stackprotector.h     |  37 ++----
 arch/x86/kernel/Makefile                  |   2 +
 arch/x86/kernel/asm-offsets_64.c          |   6 -
 arch/x86/kernel/cpu/common.c              |   8 +-
 arch/x86/kernel/head_64.S                 |  10 +-
 arch/x86/kernel/irq_64.c                  |   1 -
 arch/x86/kernel/setup_percpu.c            |  12 +-
 arch/x86/kernel/vmlinux.lds.S             |  35 ------
 arch/x86/tools/relocs.c                   | 136 +---------------------
 arch/x86/xen/xen-head.S                   |   6 +-
 include/asm-generic/vmlinux.lds.h         |   1 -
 include/linux/percpu-defs.h               |  12 --
 init/Kconfig                              |  11 +-
 kernel/kallsyms.c                         |  12 +-
 scripts/gcc-x86_32-has-stack-protector.sh |   8 --
 scripts/gcc-x86_64-has-stack-protector.sh |   4 -
 scripts/kallsyms.c                        |  80 +++----------
 scripts/link-vmlinux.sh                   |   4 -
 24 files changed, 60 insertions(+), 417 deletions(-)
 delete mode 100755 scripts/gcc-x86_32-has-stack-protector.sh
 delete mode 100755 scripts/gcc-x86_64-has-stack-protector.sh

-- 
2.41.0