[PATCH V3 0/5] riscv: ftrace: Fixup ftrace detour code & Optimization

[guoren]

From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>

The previous ftrace detour implementation fc76b8b8011 ("riscv: Using
PATCHABLE_FUNCTION_ENTRY instead of MCOUNT") contain three problems.

 - The most horrible bug is preemption panic which found by Andy [1].
   Let's disable preemption for ftrace first, and Andy could continue
   the ftrace preemption work.
 - The "-fpatchable-function-entry= CFLAG" wasted code size !RISCV_ISA_C.
 - The ftrace detour implementation wasted code size. 

The first three patches solve the above problems, and the last two
patches is from [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.

This series of patches makes function graph use ftrace directly for
riscv.

If FTRACE_WITH_REGS isn't defined, ftrace_caller keeps ftrace_graph_call
so that it can be replaced with the calling of prepare_ftrace_return by
the enable/disable helper.

As for defining FTRACE_WITH_REGS, ftrace_caller is adjusted to save the
necessary regs against the pt_regs layout, so it can reasonably call the
graph_ops::func function - ftrace_graph_func. And ftrace_graph_[regs]_call
and its enable/disable helper aren't needed.

Test log:

The tests generated by CONFIG_FTRACE_STARTUP_TEST have passed in the
local
qemu-system-riscv64 virt machine. The following is the log during
startup.

```
Nov 15 03:07:13 stage4 kernel: Testing tracer function: PASSED
Nov 15 03:07:13 stage4 kernel: Testing dynamic ftrace: PASSED
Nov 15 03:07:13 stage4 kernel: Testing dynamic ftrace ops #1: 
Nov 15 03:07:13 stage4 kernel: (1 0 1 0 0)  
Nov 15 03:07:13 stage4 kernel: (1 1 2 0 0)  
Nov 15 03:07:13 stage4 kernel: (2 1 3 0 365) 
Nov 15 03:07:13 stage4 kernel: (2 2 4 0 399) 
Nov 15 03:07:13 stage4 kernel: (3 2 4 0 146071) 
Nov 15 03:07:13 stage4 kernel: (3 3 5 0 146105) PASSED
Nov 15 03:07:13 stage4 kernel: Testing dynamic ftrace ops #2: 
Nov 15 03:07:13 stage4 kernel: (1 0 1 589 0)  
Nov 15 03:07:13 stage4 kernel: (1 1 2 635 0)  
Nov 15 03:07:13 stage4 kernel: (2 1 3 1 2)  
Nov 15 03:07:13 stage4 kernel: (2 2 4 125 126) 
Nov 15 03:07:13 stage4 kernel: (3 2 4 146001 146078) 
Nov 15 03:07:13 stage4 kernel: (3 3 5 146035 146112) PASSED
Nov 15 03:07:13 stage4 kernel: Testing ftrace recursion: PASSED
Nov 15 03:07:13 stage4 kernel: Testing ftrace recursion safe: PASSED
Nov 15 03:07:13 stage4 kernel: Testing ftrace regs: PASSED
Nov 15 03:07:13 stage4 kernel: Testing tracer nop: PASSED
Nov 15 03:07:13 stage4 kernel: Testing tracer irqsoff: PASSED
Nov 15 03:07:13 stage4 kernel: Testing tracer wakeup:
Nov 15 03:07:13 stage4 kernel: sched: DL replenish lagged too much
Nov 15 03:07:13 stage4 kernel: PASSED
Nov 15 03:07:13 stage4 kernel: Testing tracer wakeup_rt: PASSED
Nov 15 03:07:13 stage4 kernel: Testing tracer wakeup_dl: PASSED
Nov 15 03:07:13 stage4 kernel: Testing tracer function_graph: PASSED

[1]: https://lpc.events/event/16/contributions/1171/
[2]: https://lore.kernel.org/lkml/20221120084230.910152-1-suagrfillet@xxxxxxxxx/ 

Changes in V3
 - Include [2] for maintenance. [Song Shuai]

Changes in V2:
https://lore.kernel.org/linux-riscv/20220921034910.3142465-1-guoren@xxxxxxxxxx/
 - Add Signed-off for preemption fixup.

Changes in V1:
https://lore.kernel.org/linux-riscv/20220916103817.9490-1-guoren@xxxxxxxxxx/

Andy Chiu (1):
  riscv: ftrace: Fixup panic by disabling preemption

Guo Ren (2):
  riscv: ftrace: Remove wasted nops for !RISCV_ISA_C
  riscv: ftrace: Reduce the detour code size to half

Song Shuai (2):
  riscv: ftrace: Add ftrace_graph_func
  riscv: ftrace: Make ftrace_caller call ftrace_graph_func

 arch/riscv/Kconfig              |   2 +-
 arch/riscv/Makefile             |   6 +-
 arch/riscv/include/asm/ftrace.h |  63 +++++++++---
 arch/riscv/kernel/ftrace.c      |  91 ++++++----------
 arch/riscv/kernel/mcount-dyn.S  | 177 +++++++++++++++++++++-----------
 5 files changed, 202 insertions(+), 137 deletions(-)

-- 
2.36.1