[PATCH V8 0/4] riscv: Optimize function trace

From: Song Shuai
Date: Thu Mar 23 2023 - 23:33:59 EST

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The first 3 independent patches has been picked in the V7 version of
this series, this 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.

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
```

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 following tests have been passed in my local qemu-riscv64 virt
machine.

1. tests with CONFIG_FTRACE_STARTUP_TEST
2. tests of samples/ftrace/ftrace*.ko
3. manual tests with any combination of the following hooks
- function/function_graph tracer
- ftrace*.ko
- kprobe/kretprobe

For your reference, here is the log when function tracer, kretprobe and
ftrace-direct-too.ko co-hooks the handle_mm_fault function.

```
[root@stage4 tracing]# echo handle_mm_fault > set_ftrace_filter
[root@stage4 tracing]# echo 'r:myr handle_mm_fault' > kprobe_events
[root@stage4 tracing]# echo function > current_tracer
[root@stage4 tracing]# echo 1 > events/kprobes/myr/enable
[root@stage4 tracing]# insmod /root/ftrace-direct-too.ko
[root@stage4 tracing]#
[root@stage4 tracing]# cat trace | tail
cat-388 [000] ...1. 583.051438: myr:
(do_page_fault+0x16c/0x5f2 <- handle_mm_fault)
cat-388 [000] ...2. 583.057930: handle_mm_fault
<-do_page_fault
cat-388 [000] ..... 583.057990: my_direct_func:
handle mm fault vma=000000002d9fe19c address=ffffffae9b7000 flags=215
cat-388 [000] ...1. 583.058284: myr:
(do_page_fault+0x16c/0x5f2 <- handle_mm_fault)
tail-389 [001] ...2. 583.059062: handle_mm_fault
<-do_page_fault
tail-389 [001] ..... 583.059104: my_direct_func:
handle mm fault vma=0000000017f3c48e address=aaaaaabebf3000 flags=215
tail-389 [001] ...1. 583.059325: myr:
(do_page_fault+0x16c/0x5f2 <- handle_mm_fault)
tail-389 [001] ...2. 583.060371: handle_mm_fault
<-do_page_fault
tail-389 [001] ..... 583.060410: my_direct_func:
handle mm fault vma=0000000017f3c48e address=aaaaaabebf1000 flags=255
tail-389 [001] ...1. 583.060996: myr:
(do_page_fault+0x16c/0x5f2 <- handle_mm_fault)
```
Note1:

The checkpatch.pl will output some warnings on this series, like this

```
WARNING: Prefer using '"%s...", __func__' to using 'my_direct_func2',
this function's name, in a string
111: FILE: samples/ftrace/ftrace-direct-multi-modify.c:48:
+" call my_direct_func2\n"
```
The reason is that checkpatch depends on patch context providing the
function name. In the above warning, my_direct_func2 has some codeline
distance with the changed trunk, so its declaration doesn't come into
the patch, and then the warning jumps out.

You may notice the location of `my_ip` variable changes in the 2nd
patch. I did that for reducing the warnings to some extent. But killing
all the warnings will makes the patch less readable, so I stopped here.

[1]
https://lore.kernel.org/linux-riscv/CAAYs2=j3Eak9vU6xbAw0zPuoh00rh8v5C2U3fePkokZFibWs2g@xxxxxxxxxxxxxx/T/#t
[2]
https://lore.kernel.org/lkml/20221120084230.910152-1-suagrfillet@xxxxxxxxx/
[3]
https://lore.kernel.org/linux-riscv/20221123142025.1504030-1-suagrfillet@xxxxxxxxx/

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

Changes in v8:
- Fix incorrect address values in the 4nd patch
- Rebased on v6.3-rc2

Changes in v7:
https://lore.kernel.org/linux-riscv/20230112090603.1295340-1-guoren@xxxxxxxxxx/
- Fixup RESTORE_ABI_REGS by remove PT_T0(sp) overwrite.
- Add FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY
- Fixup kconfig with HAVE_SAMPLE_FTRACE_DIRECT &
HAVE_SAMPLE_FTRACE_DIRECT_MULTI

Changes in v6:
https://lore.kernel.org/linux-riscv/20230107133549.4192639-1-guoren@xxxxxxxxxx/
- 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/20221208091244.203407-1-guoren@xxxxxxxxxx/
- Sort Kconfig entries in alphabetical order.

Changes in v4:
https://lore.kernel.org/linux-riscv/20221129033230.255947-1-guoren@xxxxxxxxxx/
- Include [3] for maintenance. [Song Shuai]

Changes in V3:
https://lore.kernel.org/linux-riscv/20221123153950.2911981-1-guoren@xxxxxxxxxx/
- Include [2] for maintenance. [Song Shuai]

Song Shuai (4):
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]

arch/riscv/Kconfig | 4 +
arch/riscv/include/asm/ftrace.h | 19 ++-
arch/riscv/kernel/ftrace.c | 30 ++--
arch/riscv/kernel/mcount-dyn.S | 143 +++++++++++++++-----
samples/ftrace/ftrace-direct-modify.c | 33 +++++
samples/ftrace/ftrace-direct-multi-modify.c | 39 ++++++
samples/ftrace/ftrace-direct-multi.c | 23 ++++
samples/ftrace/ftrace-direct-too.c | 26 ++++
samples/ftrace/ftrace-direct.c | 22 +++
9 files changed, 284 insertions(+), 55 deletions(-)

--
2.20.1

Next message: Song Shuai: "[PATCH V8 1/4] riscv: select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY"
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