Re: [PATCH v13 00/20] tracing: fprobe: function_graph: Multi-function graph and fprobe on fgraph

Masami Hiramatsu
2024-09-11T00:24:39Z

Let me gently ping :)

Let me check it should be rebased on tracing/for-next again. But basically
this should be the same...

On Sun, 18 Aug 2024 21:47:53 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:

> Hi,
>
> Here is the 13th version of the series to re-implement the fprobe on
> function-graph tracer. The previous version is;
>
> https://lore.kernel.org/all/172000134410.63468.13742222887213469474.stgit@devnote2/
>
> This version is based on v6.11-rc3.
> In this version, I added a bugfix as [1/20], which should go to urgent
> branch, and dropped the performance improvement patch which was introduced
> in v12 because I found that does not work with new kernel.
>
> Overview
> --------
> This series rewrites the fprobe on this function-graph.
> The purposes of this change are;
>
> 1) Remove dependency of the rethook from fprobe so that we can reduce
> the return hook code and shadow stack.
>
> 2) Make 'ftrace_regs' the common trace interface for the function
> boundary.
>
> 1) Currently we have 2(or 3) different function return hook codes,
> the function-graph tracer and rethook (and legacy kretprobe).
> But since this is redundant and needs double maintenance cost,
> I would like to unify those. From the user's viewpoint, function-
> graph tracer is very useful to grasp the execution path. For this
> purpose, it is hard to use the rethook in the function-graph
> tracer, but the opposite is possible. (Strictly speaking, kretprobe
> can not use it because it requires 'pt_regs' for historical reasons.)
>
> 2) Now the fprobe provides the 'pt_regs' for its handler, but that is
> wrong for the function entry and exit. Moreover, depending on the
> architecture, there is no way to accurately reproduce 'pt_regs'
> outside of interrupt or exception handlers. This means fprobe should
> not use 'pt_regs' because it does not use such exceptions.
> (Conversely, kprobe should use 'pt_regs' because it is an abstract
> interface of the software breakpoint exception.)
>
> This series changes fprobe to use function-graph tracer for tracing
> function entry and exit, instead of mixture of ftrace and rethook.
> Unlike the rethook which is a per-task list of system-wide allocated
> nodes, the function graph's ret_stack is a per-task shadow stack.
> Thus it does not need to set 'nr_maxactive' (which is the number of
> pre-allocated nodes).
> Also the handlers will get the 'ftrace_regs' instead of 'pt_regs'.
> Since eBPF mulit_kprobe/multi_kretprobe events still use 'pt_regs' as
> their register interface, this changes it to convert 'ftrace_regs' to
> 'pt_regs'. Of course this conversion makes an incomplete 'pt_regs',
> so users must access only registers for function parameters or
> return value.
>
> Design
> ------
> Instead of using ftrace's function entry hook directly, the new fprobe
> is built on top of the function-graph's entry and return callbacks
> with 'ftrace_regs'.
>
> Since the fprobe requires access to 'ftrace_regs', the architecture
> must support CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS and
> CONFIG_HAVE_FTRACE_GRAPH_FUNC, which enables to call function-graph
> entry callback with 'ftrace_regs', and also
> CONFIG_HAVE_FUNCTION_GRAPH_FREGS, which passes the ftrace_regs to
> return_to_handler.
>
> All fprobes share a single function-graph ops (means shares a common
> ftrace filter) similar to the kprobe-on-ftrace. This needs another
> layer to find corresponding fprobe in the common function-graph
> callbacks, but has much better scalability, since the number of
> registered function-graph ops is limited.
>
> In the entry callback, the fprobe runs its entry_handler and saves the
> address of 'fprobe' on the function-graph's shadow stack as data. The
> return callback decodes the data to get the 'fprobe' address, and runs
> the exit_handler.
>
> The fprobe introduces two hash-tables, one is for entry callback which
> searches fprobes related to the given function address passed by entry
> callback. The other is for a return callback which checks if the given
> 'fprobe' data structure pointer is still valid. Note that it is
> possible to unregister fprobe before the return callback runs. Thus
> the address validation must be done before using it in the return
> callback.
>
> Download
> --------
> This series can be applied against the ftrace/for-next branch in
> linux-trace tree.
>
> This series can also be found below branch.
>
> https://git.kernel.org/pub/scm/linux/kernel/git/mhiramat/linux.git/log/?h=topic/fprobe-on-fgraph
>
> Thank you,
>
> ---
>
> Masami Hiramatsu (Google) (20):
> tracing: fgraph: Fix to add new fgraph_ops to array after ftrace_startup_subops()
> tracing: Add a comment about ftrace_regs definition
> tracing: Rename ftrace_regs_return_value to ftrace_regs_get_return_value
> function_graph: Pass ftrace_regs to entryfunc
> function_graph: Replace fgraph_ret_regs with ftrace_regs
> function_graph: Pass ftrace_regs to retfunc
> fprobe: Use ftrace_regs in fprobe entry handler
> fprobe: Use ftrace_regs in fprobe exit handler
> tracing: Add ftrace_partial_regs() for converting ftrace_regs to pt_regs
> tracing: Add ftrace_fill_perf_regs() for perf event
> tracing/fprobe: Enable fprobe events with CONFIG_DYNAMIC_FTRACE_WITH_ARGS
> bpf: Enable kprobe_multi feature if CONFIG_FPROBE is enabled
> ftrace: Add CONFIG_HAVE_FTRACE_GRAPH_FUNC
> fprobe: Rewrite fprobe on function-graph tracer
> tracing: Fix function timing profiler to initialize hashtable
> tracing/fprobe: Remove nr_maxactive from fprobe
> selftests: ftrace: Remove obsolate maxactive syntax check
> selftests/ftrace: Add a test case for repeating register/unregister fprobe
> Documentation: probes: Update fprobe on function-graph tracer
> fgraph: Skip recording calltime/rettime if it is not nneeded
>
>
> Documentation/trace/fprobe.rst | 42 +
> arch/arm64/Kconfig | 2
> arch/arm64/include/asm/ftrace.h | 47 +
> arch/arm64/kernel/asm-offsets.c | 12
> arch/arm64/kernel/entry-ftrace.S | 32 +
> arch/arm64/kernel/ftrace.c | 20 +
> arch/loongarch/Kconfig | 4
> arch/loongarch/include/asm/ftrace.h | 32 -
> arch/loongarch/kernel/asm-offsets.c | 12
> arch/loongarch/kernel/ftrace_dyn.c | 10
> arch/loongarch/kernel/mcount.S | 17 -
> arch/loongarch/kernel/mcount_dyn.S | 14
> arch/powerpc/Kconfig | 1
> arch/powerpc/include/asm/ftrace.h | 15
> arch/powerpc/kernel/trace/ftrace.c | 2
> arch/powerpc/kernel/trace/ftrace_64_pg.c | 10
> arch/riscv/Kconfig | 3
> arch/riscv/include/asm/ftrace.h | 26 -
> arch/riscv/kernel/ftrace.c | 17 +
> arch/riscv/kernel/mcount.S | 24 -
> arch/s390/Kconfig | 3
> arch/s390/include/asm/ftrace.h | 39 +
> arch/s390/kernel/asm-offsets.c | 6
> arch/s390/kernel/mcount.S | 9
> arch/x86/Kconfig | 4
> arch/x86/include/asm/ftrace.h | 37 +
> arch/x86/kernel/ftrace.c | 50 +-
> arch/x86/kernel/ftrace_32.S | 15
> arch/x86/kernel/ftrace_64.S | 17 -
> include/linux/fprobe.h | 57 +-
> include/linux/ftrace.h | 136 ++++
> kernel/trace/Kconfig | 23 +
> kernel/trace/bpf_trace.c | 19 -
> kernel/trace/fgraph.c | 127 +++-
> kernel/trace/fprobe.c | 638 ++++++++++++++------
> kernel/trace/ftrace.c | 10
> kernel/trace/trace.h | 6
> kernel/trace/trace_fprobe.c | 147 ++---
> kernel/trace/trace_functions_graph.c | 10
> kernel/trace/trace_irqsoff.c | 6
> kernel/trace/trace_probe_tmpl.h | 2
> kernel/trace/trace_sched_wakeup.c | 6
> kernel/trace/trace_selftest.c | 11
> lib/test_fprobe.c | 51 --
> samples/fprobe/fprobe_example.c | 4
> .../test.d/dynevent/add_remove_fprobe_repeat.tc | 19 +
> .../ftrace/test.d/dynevent/fprobe_syntax_errors.tc | 4
> 47 files changed, 1168 insertions(+), 630 deletions(-)
> create mode 100644 tools/testing/selftests/ftrace/test.d/dynevent/add_remove_fprobe_repeat.tc
>
> --
> Masami Hiramatsu (Google) <mhiramat@kernel.org>
>

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