[PATCH v2 0/4] arm64/ftrace: move to DYNAMIC_FTRACE_WITH_ARGS

[Mark Rutland <mark.rutland@arm.com>]

This series replaces arm64's support for FTRACE_WITH_REGS with support
for FTRACE_WITH_ARGS. This removes some overhead and complexity, and
removes some latent issues with inconsistent presentation of struct
pt_regs (which can only be reliably saved/restored at exception
boundaries).

The existing FTRACE_WITH_REGS support was added for two major reasons:

(1) To make it possible to use the ftrace graph tracer with pointer
    authentication, where it's necessary to snapshot/manipulate the LR
    before it is signed by the instrumented function.

(2) To make it possible to implement LIVEPATCH in future, where we need
    to hook function entry before an instrumented function manipulates
    the stack or argument registers. Practically speaking, we need to
    preserve the argument/return registers, PC, LR, and SP.

Neither of these requires the full set of pt_regs, and only requires us
to save/restore a subset of registers used for passing
arguments/return-values and context/return information (which is the
minimum set we always need to save/restore today).

As there is no longer a need to save different sets of registers for
different features, we no longer need distinct `ftrace_caller` and
`ftrace_regs_caller` trampolines. This allows the trampoline assembly to
be simpler, and simplifies code which previously had to handle the two
trampolines.

I've tested this with the ftrace selftests, where there are no
unexpected failures.

I plan to build atop this with subsequent patches to add per-callsite
ftrace_ops, and I'm sending these patches on their own as I think they
make sense regardless.

Since v1 [1]:
* Change ifdeferry per Steve's request
* Add ftrace_regs_query_register_offset() per Masami's request
* Fix a bunch of typos

[1] https://lore.kernel.org/lkml/20221024140846.3555435-1-mark.rutland@arm.com

This series can be found in my 'arm64/ftrace/minimal-regs' branch on
kernel.org:

  https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/
  git://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git

This version is tagged as:

  arm64-ftrace-minimal-regs-20221103

Thanks,
Mark.

Mark Rutland (4):
  ftrace: pass fregs to arch_ftrace_set_direct_caller()
  ftrace: rename ftrace_instruction_pointer_set() ->
    ftrace_regs_set_instruction_pointer()
  ftrace: abstract DYNAMIC_FTRACE_WITH_ARGS accesses
  ftrace: arm64: move from REGS to ARGS

 arch/arm64/Kconfig                |  18 +++--
 arch/arm64/Makefile               |   2 +-
 arch/arm64/include/asm/ftrace.h   |  72 ++++++++++++++++--
 arch/arm64/kernel/asm-offsets.c   |  13 ++++
 arch/arm64/kernel/entry-ftrace.S  | 117 ++++++++++++------------------
 arch/arm64/kernel/ftrace.c        |  82 ++++++++++++---------
 arch/arm64/kernel/module.c        |   3 -
 arch/powerpc/include/asm/ftrace.h |  24 +++++-
 arch/s390/include/asm/ftrace.h    |  29 +++++++-
 arch/x86/include/asm/ftrace.h     |  49 +++++++++----
 include/linux/ftrace.h            |  47 +++++++++---
 kernel/livepatch/patch.c          |   2 +-
 kernel/trace/Kconfig              |   6 +-
 kernel/trace/ftrace.c             |   3 +-
 14 files changed, 309 insertions(+), 158 deletions(-)

-- 
2.30.2