riscv: Optimize function trace

Changes in V11:

- append a patch that makes the DIRECT_CALL samples support RV32I in
  this series fixing the rv32 build failure reported by Palmer

- validated with ftrace boottime selftest and manual sample modules test
  in qemu-system for RV32I and RV64I

This series optimizes function trace. The first 3 independent 
patches has been picked in the V7 version of this series, the
subsequent version continues the following 4 patches:

select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY [1] (patch 1)
==========================================================

In RISC-V, -fpatchable-function-entry option is used to support
dynamic ftrace in this commit afc76b8b8011 ("riscv: Using
PATCHABLE_FUNCTION_ENTRY instead of MCOUNT"). So recordmcount
don't have to be called to create the __mcount_loc section before
the vmlinux linking.

Here selects FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY to tell
Makefile not to run recordmcount.

Make function graph use ftrace directly [2] (patch 2)
======================================================== 

In RISC-V architecture, when we enable the ftrace_graph tracer on some
functions, the function tracings on other functions will suffer extra
graph tracing work. In essence, graph_ops isn't limited by its func_hash
due to the global ftrace_graph_[regs]_call label. That should be
corrected.

What inspires me is the commit 0c0593b45c9b ("x86/ftrace: Make function
graph use ftrace directly") that uses graph_ops::func function to
install return_hooker and makes the function called against its
func_hash.

Add WITH_DIRECT_CALLS support [3] (patch 3, 4)
==============================================

This series adds DYNAMIC_FTRACE_WITH_DIRECT_CALLS support for RISC-V.
SAMPLE_FTRACE_DIRECT and SAMPLE_FTRACE_DIRECT_MULTI are also included
here as the samples for testing DIRECT_CALLS related interface.

First, select the DYNAMIC_FTRACE_WITH_DIRECT_CALLS to provide 
register_ftrace_direct[_multi] interfaces allowing user to register 
the customed trampoline (direct_caller) as the mcount for one or 
more target functions. And modify_ftrace_direct[_multi] are also 
provided for modify direct_caller.

At the same time, the samples in ./samples/ftrace/ can be built
as kerenl module for testing these interfaces with SAMPLE_FTRACE_DIRECT
and SAMPLE_FTRACE_DIRECT_MULTI selected.

Second, to make the direct_caller and the other ftrace hooks
(eg. function/fgraph tracer, k[ret]probes) co-exist, a temporary
register
are nominated to store the address of direct_caller in
ftrace_regs_caller.
After the setting of the address direct_caller by direct_ops->func and
the RESTORE_REGS in ftrace_regs_caller, direct_caller will be jumped to
by the `jr` inst.

The series's old changes related these patches
==========================================

Changes in v10:
https://lore.kernel.org/all/20230511093234.3123181-1-suag...

- add Acked-by from Björn Töpel in patch 2 and patch 4 
- replace `move` with `mv` in patch3 
- prettify patch 2/4 with proper tabs

Changes in v9:
https://lore.kernel.org/linux-riscv/20230510101857.295395...

1. add Acked-by from Björn Töpel in patch 1

2. rebase patch2/patch3 on Linux v6.4-rc1

  - patch 2: to make the `SAVE_ABI_REGS` configurable, revert the
    modification of mcount-dyn.S from commit (45b32b946a97 "riscv:
entry: Consolidate general regs saving/restoring")

  - patch 3: to pass the trace_selftest, add the implement of
    `ftrace_stub_direct_tramp` from commit (fee86a4ed536 "ftrace:
selftest: remove broken trace_direct_tramp") ; and fixup the context
conflict in Kconfig 

Changes in v8:
https://lore.kernel.org/linux-riscv/20230324033342.317797...
 - Fix incorrect address values in the 4nd patch 
 - Rebased on v6.3-rc2

Changes in v7:
https://lore.kernel.org/linux-riscv/20230112090603.129534...
 - Fixup RESTORE_ABI_REGS by remove PT_T0(sp) overwrite.
 - Add FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY [1]
 - Fixup kconfig with HAVE_SAMPLE_FTRACE_DIRECT &
   HAVE_SAMPLE_FTRACE_DIRECT_MULTI

Changes in v6:
https://lore.kernel.org/linux-riscv/20230107133549.419263...
 - Replace 8 with MCOUNT_INSN_SIZE
 - Replace "REG_L a1, PT_RA(sp)" with "mv a1, ra"
 - Add Evgenii Shatokhin comment

Changes in v5:
https://lore.kernel.org/linux-riscv/20221208091244.203407...
 - Sort Kconfig entries in alphabetical order.

Changes in v4:
https://lore.kernel.org/linux-riscv/20221129033230.255947...
 - Include [3] for maintenance. [Song Shuai]

Changes in V3:
https://lore.kernel.org/linux-riscv/20221123153950.291198...
 - Include [2] for maintenance. [Song Shuai]

[1]: https://lore.kernel.org/linux-riscv/CAAYs2=j3Eak9vU6xbAw0...
[2]: https://lore.kernel.org/lkml/20221120084230.910152-1-suag...
[3]: https://lore.kernel.org/linux-riscv/20221123142025.150403... 

Song Shuai (5):
  riscv: select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY
  riscv: ftrace: Add ftrace_graph_func
  riscv: ftrace: Add DYNAMIC_FTRACE_WITH_DIRECT_CALLS support
  samples: ftrace: Add riscv support for SAMPLE_FTRACE_DIRECT[_MULTI]
  samples: ftrace: Make the riscv samples support RV32I

 arch/riscv/Kconfig                          |   4 +
 arch/riscv/include/asm/ftrace.h             |  19 +-
 arch/riscv/kernel/ftrace.c                  |  30 ++-
 arch/riscv/kernel/mcount-dyn.S              | 200 ++++++++++++++++----
 samples/ftrace/ftrace-direct-modify.c       |  35 ++++
 samples/ftrace/ftrace-direct-multi-modify.c |  41 ++++
 samples/ftrace/ftrace-direct-multi.c        |  25 +++
 samples/ftrace/ftrace-direct-too.c          |  28 +++
 samples/ftrace/ftrace-direct.c              |  24 +++
 9 files changed, 350 insertions(+), 56 deletions(-)

-- 
2.20.1