Re: [PATCH v2 4/4] ftrace: Add arguments to function tracer

Masami Hiramatsu
2024-12-25T14:21:07Z

On Mon, 23 Dec 2024 15:13:51 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> From: Sven Schnelle <svens@linux.ibm.com>
>
> Wire up the code to print function arguments in the function tracer.
> This functionality can be enabled/disabled during runtime with
> options/func-args.
>
> ping-689 [004] b.... 77.170220: dummy_xmit(skb = 0x82904800, dev = 0x882d0000) <-dev_hard_start_xmit
>

Looks good to me.

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

> Co-developed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
> Changes since v1: https://lore.kernel.org/20240904065908.1009086-8-svens@linux.ibm.com
>
> - Save only the arguments into the ring buffer and not the ftrace_regs
> as the ftrace_regs should be opaque from generic code.
>
> - Have the function tracer event be dynamic so that it can hold an array
> of arguments after the entry.
>
> kernel/trace/trace.c | 12 ++++++--
> kernel/trace/trace.h | 3 +-
> kernel/trace/trace_entries.h | 5 ++--
> kernel/trace/trace_functions.c | 46 +++++++++++++++++++++++++++----
> kernel/trace/trace_irqsoff.c | 4 +--
> kernel/trace/trace_output.c | 18 ++++++++++--
> kernel/trace/trace_sched_wakeup.c | 4 +--
> 7 files changed, 75 insertions(+), 17 deletions(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index be62f0ea1814..3c0ffdcdcb7e 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -2897,13 +2897,16 @@ trace_buffer_unlock_commit_nostack(struct trace_buffer *buffer,
>
> void
> trace_function(struct trace_array *tr, unsigned long ip, unsigned long
> - parent_ip, unsigned int trace_ctx)
> + parent_ip, unsigned int trace_ctx, struct ftrace_regs *fregs)
> {
> struct trace_buffer *buffer = tr->array_buffer.buffer;
> struct ring_buffer_event *event;
> struct ftrace_entry *entry;
> + int size = sizeof(*entry);
>
> - event = __trace_buffer_lock_reserve(buffer, TRACE_FN, sizeof(*entry),
> + size += FTRACE_REGS_MAX_ARGS * !!fregs * sizeof(long);
> +
> + event = __trace_buffer_lock_reserve(buffer, TRACE_FN, size,
> trace_ctx);
> if (!event)
> return;
> @@ -2911,6 +2914,11 @@ trace_function(struct trace_array *tr, unsigned long ip, unsigned long
> entry->ip = ip;
> entry->parent_ip = parent_ip;
>
> + if (fregs) {
> + for (int i = 0; i < FTRACE_REGS_MAX_ARGS; i++)
> + entry->args[i] = ftrace_regs_get_argument(fregs, i);
> + }
> +
> if (static_branch_unlikely(&trace_function_exports_enabled))
> ftrace_exports(event, TRACE_EXPORT_FUNCTION);
> __buffer_unlock_commit(buffer, event);
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 6f67bbc17bed..3d4a5ec9ee55 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -685,7 +685,8 @@ unsigned long trace_total_entries(struct trace_array *tr);
> void trace_function(struct trace_array *tr,
> unsigned long ip,
> unsigned long parent_ip,
> - unsigned int trace_ctx);
> + unsigned int trace_ctx,
> + struct ftrace_regs *regs);
> void trace_graph_function(struct trace_array *tr,
> unsigned long ip,
> unsigned long parent_ip,
> diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
> index 254491b545c3..11288dc4f59b 100644
> --- a/kernel/trace/trace_entries.h
> +++ b/kernel/trace/trace_entries.h
> @@ -61,8 +61,9 @@ FTRACE_ENTRY_REG(function, ftrace_entry,
> TRACE_FN,
>
> F_STRUCT(
> - __field_fn( unsigned long, ip )
> - __field_fn( unsigned long, parent_ip )
> + __field_fn( unsigned long, ip )
> + __field_fn( unsigned long, parent_ip )
> + __dynamic_array( unsigned long, args )
> ),
>
> F_printk(" %ps <-- %ps",
> diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
> index d358c9935164..1f4f02df6f8c 100644
> --- a/kernel/trace/trace_functions.c
> +++ b/kernel/trace/trace_functions.c
> @@ -25,6 +25,9 @@ static void
> function_trace_call(unsigned long ip, unsigned long parent_ip,
> struct ftrace_ops *op, struct ftrace_regs *fregs);
> static void
> +function_args_trace_call(unsigned long ip, unsigned long parent_ip,
> + struct ftrace_ops *op, struct ftrace_regs *fregs);
> +static void
> function_stack_trace_call(unsigned long ip, unsigned long parent_ip,
> struct ftrace_ops *op, struct ftrace_regs *fregs);
> static void
> @@ -42,9 +45,10 @@ enum {
> TRACE_FUNC_NO_OPTS = 0x0, /* No flags set. */
> TRACE_FUNC_OPT_STACK = 0x1,
> TRACE_FUNC_OPT_NO_REPEATS = 0x2,
> + TRACE_FUNC_OPT_ARGS = 0x4,
>
> /* Update this to next highest bit. */
> - TRACE_FUNC_OPT_HIGHEST_BIT = 0x4
> + TRACE_FUNC_OPT_HIGHEST_BIT = 0x8
> };
>
> #define TRACE_FUNC_OPT_MASK (TRACE_FUNC_OPT_HIGHEST_BIT - 1)
> @@ -114,6 +118,8 @@ static ftrace_func_t select_trace_function(u32 flags_val)
> switch (flags_val & TRACE_FUNC_OPT_MASK) {
> case TRACE_FUNC_NO_OPTS:
> return function_trace_call;
> + case TRACE_FUNC_OPT_ARGS:
> + return function_args_trace_call;
> case TRACE_FUNC_OPT_STACK:
> return function_stack_trace_call;
> case TRACE_FUNC_OPT_NO_REPEATS:
> @@ -220,7 +226,34 @@ function_trace_call(unsigned long ip, unsigned long parent_ip,
>
> data = this_cpu_ptr(tr->array_buffer.data);
> if (!atomic_read(&data->disabled))
> - trace_function(tr, ip, parent_ip, trace_ctx);
> + trace_function(tr, ip, parent_ip, trace_ctx, NULL);
> +
> + ftrace_test_recursion_unlock(bit);
> +}
> +
> +static void
> +function_args_trace_call(unsigned long ip, unsigned long parent_ip,
> + struct ftrace_ops *op, struct ftrace_regs *fregs)
> +{
> + struct trace_array *tr = op->private;
> + struct trace_array_cpu *data;
> + unsigned int trace_ctx;
> + int bit;
> + int cpu;
> +
> + if (unlikely(!tr->function_enabled))
> + return;
> +
> + bit = ftrace_test_recursion_trylock(ip, parent_ip);
> + if (bit < 0)
> + return;
> +
> + trace_ctx = tracing_gen_ctx();
> +
> + cpu = smp_processor_id();
> + data = per_cpu_ptr(tr->array_buffer.data, cpu);
> + if (!atomic_read(&data->disabled))
> + trace_function(tr, ip, parent_ip, trace_ctx, fregs);
>
> ftrace_test_recursion_unlock(bit);
> }
> @@ -270,7 +303,7 @@ function_stack_trace_call(unsigned long ip, unsigned long parent_ip,
>
> if (likely(disabled == 1)) {
> trace_ctx = tracing_gen_ctx_flags(flags);
> - trace_function(tr, ip, parent_ip, trace_ctx);
> + trace_function(tr, ip, parent_ip, trace_ctx, NULL);
> #ifdef CONFIG_UNWINDER_FRAME_POINTER
> if (ftrace_pids_enabled(op))
> skip++;
> @@ -351,7 +384,7 @@ function_no_repeats_trace_call(unsigned long ip, unsigned long parent_ip,
> trace_ctx = tracing_gen_ctx_flags(flags);
> process_repeats(tr, ip, parent_ip, last_info, trace_ctx);
>
> - trace_function(tr, ip, parent_ip, trace_ctx);
> + trace_function(tr, ip, parent_ip, trace_ctx, NULL);
>
> out:
> ftrace_test_recursion_unlock(bit);
> @@ -391,7 +424,7 @@ function_stack_no_repeats_trace_call(unsigned long ip, unsigned long parent_ip,
> trace_ctx = tracing_gen_ctx_flags(flags);
> process_repeats(tr, ip, parent_ip, last_info, trace_ctx);
>
> - trace_function(tr, ip, parent_ip, trace_ctx);
> + trace_function(tr, ip, parent_ip, trace_ctx, NULL);
> __trace_stack(tr, trace_ctx, STACK_SKIP);
> }
>
> @@ -405,6 +438,9 @@ static struct tracer_opt func_opts[] = {
> { TRACER_OPT(func_stack_trace, TRACE_FUNC_OPT_STACK) },
> #endif
> { TRACER_OPT(func-no-repeats, TRACE_FUNC_OPT_NO_REPEATS) },
> +#ifdef CONFIG_FUNCTION_TRACE_ARGS
> + { TRACER_OPT(func-args, TRACE_FUNC_OPT_ARGS) },
> +#endif
> { } /* Always set a last empty entry */
> };
>
> diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
> index 504de7a05498..68ce152dbb8c 100644
> --- a/kernel/trace/trace_irqsoff.c
> +++ b/kernel/trace/trace_irqsoff.c
> @@ -150,7 +150,7 @@ irqsoff_tracer_call(unsigned long ip, unsigned long parent_ip,
>
> trace_ctx = tracing_gen_ctx_flags(flags);
>
> - trace_function(tr, ip, parent_ip, trace_ctx);
> + trace_function(tr, ip, parent_ip, trace_ctx, fregs);
>
> atomic_dec(&data->disabled);
> }
> @@ -280,7 +280,7 @@ __trace_function(struct trace_array *tr,
> if (is_graph(tr))
> trace_graph_function(tr, ip, parent_ip, trace_ctx);
> else
> - trace_function(tr, ip, parent_ip, trace_ctx);
> + trace_function(tr, ip, parent_ip, trace_ctx, NULL);
> }
>
> #else
> diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> index 40d6c7a9e0c4..aed6758416a0 100644
> --- a/kernel/trace/trace_output.c
> +++ b/kernel/trace/trace_output.c
> @@ -1079,12 +1079,15 @@ enum print_line_t trace_nop_print(struct trace_iterator *iter, int flags,
> }
>
> static void print_fn_trace(struct trace_seq *s, unsigned long ip,
> - unsigned long parent_ip, long delta, int flags)
> + unsigned long parent_ip, long delta,
> + unsigned long *args, int flags)
> {
> ip += delta;
> parent_ip += delta;
>
> seq_print_ip_sym(s, ip, flags);
> + if (args)
> + print_function_args(s, args, ip);
>
> if ((flags & TRACE_ITER_PRINT_PARENT) && parent_ip) {
> trace_seq_puts(s, " <-");
> @@ -1098,10 +1101,19 @@ static enum print_line_t trace_fn_trace(struct trace_iterator *iter, int flags,
> {
> struct ftrace_entry *field;
> struct trace_seq *s = &iter->seq;
> + unsigned long *args;
> + int args_size;
>
> trace_assign_type(field, iter->ent);
>
> - print_fn_trace(s, field->ip, field->parent_ip, iter->tr->text_delta, flags);
> + args_size = iter->ent_size - offsetof(struct ftrace_entry, args);
> + if (args_size >= FTRACE_REGS_MAX_ARGS * sizeof(long))
> + args = field->args;
> + else
> + args = NULL;
> +
> + print_fn_trace(s, field->ip, field->parent_ip, iter->tr->text_delta,
> + args, flags);
> trace_seq_putc(s, '\n');
>
> return trace_handle_return(s);
> @@ -1774,7 +1786,7 @@ trace_func_repeats_print(struct trace_iterator *iter, int flags,
>
> trace_assign_type(field, iter->ent);
>
> - print_fn_trace(s, field->ip, field->parent_ip, iter->tr->text_delta, flags);
> + print_fn_trace(s, field->ip, field->parent_ip, iter->tr->text_delta, NULL, flags);
> trace_seq_printf(s, " (repeats: %u, last_ts:", field->count);
> trace_print_time(s, iter,
> iter->ts - FUNC_REPEATS_GET_DELTA_TS(field));
> diff --git a/kernel/trace/trace_sched_wakeup.c b/kernel/trace/trace_sched_wakeup.c
> index 8165382a174a..19b0205b91dd 100644
> --- a/kernel/trace/trace_sched_wakeup.c
> +++ b/kernel/trace/trace_sched_wakeup.c
> @@ -226,7 +226,7 @@ wakeup_tracer_call(unsigned long ip, unsigned long parent_ip,
> return;
>
> local_irq_save(flags);
> - trace_function(tr, ip, parent_ip, trace_ctx);
> + trace_function(tr, ip, parent_ip, trace_ctx, fregs);
> local_irq_restore(flags);
>
> atomic_dec(&data->disabled);
> @@ -311,7 +311,7 @@ __trace_function(struct trace_array *tr,
> if (is_graph(tr))
> trace_graph_function(tr, ip, parent_ip, trace_ctx);
> else
> - trace_function(tr, ip, parent_ip, trace_ctx);
> + trace_function(tr, ip, parent_ip, trace_ctx, NULL);
> }
>
> static int wakeup_flag_changed(struct trace_array *tr, u32 mask, int set)
> --
> 2.45.2
>
>

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