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

Steven Rostedt
2024-12-23T20:14:50Z

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

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