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

  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(-)
  

On Thu,  3 Nov 2022 17:05:16 +0000
Mark Rutland <mark.rutland@arm.com> wrote:

> 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.

Were there any "expected" 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


So I ran this on top of my code through all my ftrace tests (for x86) and
it didn't cause any regressions.

Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>

-- Steve
  

On Tue, Nov 15, 2022 at 10:01:48AM -0500, Steven Rostedt wrote:
> On Thu,  3 Nov 2022 17:05:16 +0000
> Mark Rutland <mark.rutland@arm.com> wrote:
> 
> > 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.
> 
> Were there any "expected" failures?

Ah; sorry, I had meant to include the results here.

With this series applied atop v6.1-rc4 and using the ftrace selftests from that
tree, my results were the same as with baseline v6.1-rc4:

| # of passed:  104
| # of failed:  0
| # of unresolved:  7
| # of untested:  0
| # of unsupported:  2
| # of xfailed:  1
| # of undefined(test bug):  0

Where the non-passing tests were:

| [8] Test ftrace direct functions against tracers        [UNRESOLVED]
| [9] Test ftrace direct functions against kprobes        [UNRESOLVED]

... as direct functions aren't supported on arm64 (both before and after this
series).

| [16] Generic dynamic event - check if duplicate events are caught       [UNSUPPORTED]
| [74] event trigger - test inter-event histogram trigger eprobe on synthetic event       [UNSUPPORTED]

... which are due to a bug in the tests fixed by:

  https://lore.kernel.org/all/20221010074207.714077-1-svens@linux.ibm.com/

... and they both pass with that applied.

| [22] Test trace_printk from module      [UNRESOLVED]
| [31] ftrace - function trace on module  [UNRESOLVED]
| [51] Kprobe dynamic event - probing module      [UNRESOLVED]
| [61] test for the preemptirqsoff tracer [UNRESOLVED]

... which are because my test environment didn't have modules.

| [62] Meta-selftest: Checkbashisms       [UNRESOLVED]

... which is irrelevant for this series.

| [65] event trigger - test inter-event histogram trigger expected fail actions   [XFAIL]

... which is expected.

[...]

> So I ran this on top of my code through all my ftrace tests (for x86) and
> it didn't cause any regressions.
> 
> Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Thanks!

Mark.
  

On Thu,  3 Nov 2022 17:05:16 +0000
Mark Rutland <mark.rutland@arm.com> wrote:

> 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.

Thanks! this series looks good to me.

Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

So it is the good time to rewrite the new fprobe event handler
based on these interfaces :)

> 
> 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
>
  

On Thu, 3 Nov 2022 17:05:16 +0000, Mark Rutland wrote:
> 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:
> 
> [...]

Applied to arm64 (for-next/ftrace), thanks!

[1/4] ftrace: pass fregs to arch_ftrace_set_direct_caller()
      https://git.kernel.org/arm64/c/9705bc709604
[2/4] ftrace: rename ftrace_instruction_pointer_set() -> ftrace_regs_set_instruction_pointer()
      https://git.kernel.org/arm64/c/0ef86097f127
[3/4] ftrace: abstract DYNAMIC_FTRACE_WITH_ARGS accesses
      https://git.kernel.org/arm64/c/94d095ffa0e1
[4/4] ftrace: arm64: move from REGS to ARGS
      https://git.kernel.org/arm64/c/26299b3f6ba2

Cheers,