[PATCH v2 0/6] Out-of-line static calls for powerpc64 ELF V2

[Benjamin Gray <bgray@linux.ibm.com>]

Implementation of out-of-line static calls for PowerPC 64-bit ELF V2 ABI.
Static calls patch an indirect branch into a direct branch at runtime.
Out-of-line specifically has a caller directly call a trampoline, and
the trampoline gets patched to directly call the target.

Previous version here:
https://lore.kernel.org/all/20220916062330.430468-1-bgray@linux.ibm.com/

I couldn't see a dedicated ftrace benchmark in the kernel, but my own
benchmarking showed no significant impact to ftrace activation.

The __patch_memory function is meant to be accessed through the size checking
patch_memory wrapper. I don't think there's a way to expose the macro without
also exposing __patch_memory though. I considered making the type an explicit
macro param, but using the value type seemed more ergonomic.

V2:
Mostly accounting for feedback from Christophe:
* Code patching rewritten
    - Rename to *_memory
    - Use __always_inline to get the compiler to realise it can
      collapse all the sub-functions
    - Pass data directly instead of through a pointer, elliding a redundant load
    - Flush the last byte of data too (technically redundant if an instrucion, but
      saves a conditional branch + the isync will be the bottleneck).
    - Handle a non-cohenrent icache, assume a coherent dcache
    - Handle when we don't assume a 64 byte icache on 64-bits
    - Flatten the poke address init and teardown
    - Check the data size in patch_memory at build time
      (inline function was suggested, but a macro makes checking
       based on the data type easier).
    - It builds now on 32 bit and without strict RWX
* Static call enabling is no longer configurable
* Refactored arch_static_call_transform to minimise casting
* Made the KUnit tests more robust (previously they changed non-volatile
  registers in the init hook, but that's incorrect because it returns to
  the KUnit framework before the test case is called).
* Some other minor refactoring in other patches


Benjamin Gray (6):
  powerpc/code-patching: Implement generic text patching function
  powerpc/module: Handle caller-saved TOC in module linker
  powerpc/module: Optimise nearby branches in ELF V2 ABI stub
  static_call: Move static call selftest to static_call_selftest.c
  powerpc/64: Add support for out-of-line static calls
  powerpc/64: Add tests for out-of-line static calls

 arch/powerpc/Kconfig                     |  12 +-
 arch/powerpc/include/asm/code-patching.h |   8 +
 arch/powerpc/include/asm/static_call.h   |  80 +++++++-
 arch/powerpc/kernel/Makefile             |   4 +-
 arch/powerpc/kernel/module_64.c          |  27 ++-
 arch/powerpc/kernel/static_call.c        | 151 +++++++++++++-
 arch/powerpc/kernel/static_call_test.c   | 251 +++++++++++++++++++++++
 arch/powerpc/kernel/static_call_test.h   |  56 +++++
 arch/powerpc/lib/code-patching.c         |  90 +++++---
 kernel/Makefile                          |   1 +
 kernel/static_call_inline.c              |  43 ----
 kernel/static_call_selftest.c            |  41 ++++
 12 files changed, 682 insertions(+), 82 deletions(-)
 create mode 100644 arch/powerpc/kernel/static_call_test.c
 create mode 100644 arch/powerpc/kernel/static_call_test.h
 create mode 100644 kernel/static_call_selftest.c


base-commit: 3d7a198cfdb47405cfb4a3ea523876569fe341e6
--
2.37.3