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Message-Id: <20240912084926.6d4c5768a538fb5946e31bda@kernel.org> Date: Thu, 12 Sep 2024 08:49:26 +0900 From: Masami Hiramatsu (Google) <mhiramat@...nel.org> To: Masami Hiramatsu (Google) <mhiramat@...nel.org> Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>, Steven Rostedt <rostedt@...dmis.org>, Florent Revest <revest@...omium.org>, linux-trace-kernel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, bpf <bpf@...r.kernel.org>, Sven Schnelle <svens@...ux.ibm.com>, Alexei Starovoitov <ast@...nel.org>, Jiri Olsa <jolsa@...nel.org>, Arnaldo Carvalho de Melo <acme@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Alan Maguire <alan.maguire@...cle.com>, Mark Rutland <mark.rutland@....com>, Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, Guo Ren <guoren@...nel.org> Subject: Re: [PATCH v13 00/20] tracing: fprobe: function_graph: Multi-function graph and fprobe on fgraph On Wed, 11 Sep 2024 09:24:34 +0900 Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote: > Let me gently ping :) > > Let me check it should be rebased on tracing/for-next again. But basically > this should be the same... I found a build error on riscv. Let me fix that. Thanks, > > On Sun, 18 Aug 2024 21:47:53 +0900 > "Masami Hiramatsu (Google)" <mhiramat@...nel.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@...nel.org> > > > > > -- > Masami Hiramatsu (Google) <mhiramat@...nel.org> -- Masami Hiramatsu (Google) <mhiramat@...nel.org>
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