[PATCH v2 2/4] ftrace: Add support for function argument to graph 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 graph
tracer. This functionality can be enabled/disabled during runtime with
options/funcgraph-args.

Example usage:

6) | dummy_xmit [dummy](skb = 0x8887c100, dev = 0x872ca000) {
6) | consume_skb(skb = 0x8887c100) {
6) | skb_release_head_state(skb = 0x8887c100) {
6) 0.178 us | sock_wfree(skb = 0x8887c100)
6) 0.627 us | }

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/20240904065908.1009086-7-svens@linux.ibm.com

- Record just FTRACE_REGS_MAX_ARGS into the ring buffer and not the
entire ftrace_regs structure, as that structure should be opaque
from generic code.

- Make the function graph entry event have a dynamic size, so that an
array of arguments may be added in the ring buffer after it.

kernel/trace/Kconfig | 6 ++
kernel/trace/trace.h | 1 +
kernel/trace/trace_entries.h | 7 +-
kernel/trace/trace_functions_graph.c | 147 +++++++++++++++++++++------
4 files changed, 125 insertions(+), 36 deletions(-)

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 60412c1012ef..033fba0633cf 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -268,6 +268,12 @@ config FUNCTION_TRACE_ARGS
depends on HAVE_FUNCTION_ARG_ACCESS_API
depends on DEBUG_INFO_BTF
default y
+ help
+ If supported with function argument access API and BTF, then
+ the function tracer and function graph tracer will support printing
+ of function arguments. This feature is off by default, and can be
+ enabled via the trace option func-args (for the function tracer) and
+ funcgraph-args (for the function graph tracer)

config DYNAMIC_FTRACE
bool "enable/disable function tracing dynamically"
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index ad9f008d7dd7..6f67bbc17bed 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -887,6 +887,7 @@ static __always_inline bool ftrace_hash_empty(struct ftrace_hash *hash)
#define TRACE_GRAPH_PRINT_RETVAL 0x800
#define TRACE_GRAPH_PRINT_RETVAL_HEX 0x1000
#define TRACE_GRAPH_PRINT_RETADDR 0x2000
+#define TRACE_GRAPH_ARGS 0x4000
#define TRACE_GRAPH_PRINT_FILL_SHIFT 28
#define TRACE_GRAPH_PRINT_FILL_MASK (0x3 << TRACE_GRAPH_PRINT_FILL_SHIFT)

diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
index 82fd174ebbe0..254491b545c3 100644
--- a/kernel/trace/trace_entries.h
+++ b/kernel/trace/trace_entries.h
@@ -72,17 +72,18 @@ FTRACE_ENTRY_REG(function, ftrace_entry,
);

/* Function call entry */
-FTRACE_ENTRY_PACKED(funcgraph_entry, ftrace_graph_ent_entry,
+FTRACE_ENTRY(funcgraph_entry, ftrace_graph_ent_entry,

TRACE_GRAPH_ENT,

F_STRUCT(
__field_struct( struct ftrace_graph_ent, graph_ent )
__field_packed( unsigned long, graph_ent, func )
- __field_packed( int, graph_ent, depth )
+ __field_packed( unsigned long, graph_ent, depth )
+ __dynamic_array(unsigned long, args )
),

- F_printk("--> %ps (%d)", (void *)__entry->func, __entry->depth)
+ F_printk("--> %ps (%lu)", (void *)__entry->func, __entry->depth)
);

#ifdef CONFIG_FUNCTION_GRAPH_RETADDR
diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index d0e4f412c298..c8eda9bebdf4 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -12,6 +12,8 @@
#include <linux/interrupt.h>
#include <linux/slab.h>
#include <linux/fs.h>
+#include <linux/btf.h>
+#include <linux/bpf.h>

#include "trace.h"
#include "trace_output.h"
@@ -70,6 +72,10 @@ static struct tracer_opt trace_opts[] = {
#ifdef CONFIG_FUNCTION_GRAPH_RETADDR
/* Display function return address ? */
{ TRACER_OPT(funcgraph-retaddr, TRACE_GRAPH_PRINT_RETADDR) },
+#endif
+#ifdef CONFIG_FUNCTION_TRACE_ARGS
+ /* Display function arguments ? */
+ { TRACER_OPT(funcgraph-args, TRACE_GRAPH_ARGS) },
#endif
/* Include sleep time (scheduled out) between entry and return */
{ TRACER_OPT(sleep-time, TRACE_GRAPH_SLEEP_TIME) },
@@ -110,25 +116,41 @@ static void
print_graph_duration(struct trace_array *tr, unsigned long long duration,
struct trace_seq *s, u32 flags);

-int __trace_graph_entry(struct trace_array *tr,
- struct ftrace_graph_ent *trace,
- unsigned int trace_ctx)
+static int __graph_entry(struct trace_array *tr, struct ftrace_graph_ent *trace,
+ unsigned int trace_ctx, struct ftrace_regs *fregs)
{
struct ring_buffer_event *event;
struct trace_buffer *buffer = tr->array_buffer.buffer;
struct ftrace_graph_ent_entry *entry;
+ int size;

- event = trace_buffer_lock_reserve(buffer, TRACE_GRAPH_ENT,
- sizeof(*entry), trace_ctx);
+ /* If fregs is defined, add FTRACE_REGS_MAX_ARGS long size words */
+ size = sizeof(*entry) + (FTRACE_REGS_MAX_ARGS * !!fregs * sizeof(long));
+
+ event = trace_buffer_lock_reserve(buffer, TRACE_GRAPH_ENT, size, trace_ctx);
if (!event)
return 0;
- entry = ring_buffer_event_data(event);
- entry->graph_ent = *trace;
+
+ entry = ring_buffer_event_data(event);
+ entry->graph_ent = *trace;
+
+ if (fregs) {
+ for (int i = 0; i < FTRACE_REGS_MAX_ARGS; i++)
+ entry->args[i] = ftrace_regs_get_argument(fregs, i);
+ }
+
trace_buffer_unlock_commit_nostack(buffer, event);

return 1;
}

+int __trace_graph_entry(struct trace_array *tr,
+ struct ftrace_graph_ent *trace,
+ unsigned int trace_ctx)
+{
+ return __graph_entry(tr, trace, trace_ctx, NULL);
+}
+
#ifdef CONFIG_FUNCTION_GRAPH_RETADDR
int __trace_graph_retaddr_entry(struct trace_array *tr,
struct ftrace_graph_ent *trace,
@@ -174,9 +196,9 @@ struct fgraph_times {
unsigned long long sleeptime; /* may be optional! */
};

-int trace_graph_entry(struct ftrace_graph_ent *trace,
- struct fgraph_ops *gops,
- struct ftrace_regs *fregs)
+static int graph_entry(struct ftrace_graph_ent *trace,
+ struct fgraph_ops *gops,
+ struct ftrace_regs *fregs)
{
unsigned long *task_var = fgraph_get_task_var(gops);
struct trace_array *tr = gops->private;
@@ -248,7 +270,7 @@ int trace_graph_entry(struct ftrace_graph_ent *trace,

ret = __trace_graph_retaddr_entry(tr, trace, trace_ctx, retaddr);
} else
- ret = __trace_graph_entry(tr, trace, trace_ctx);
+ ret = __graph_entry(tr, trace, trace_ctx, fregs);
} else {
ret = 0;
}
@@ -259,6 +281,20 @@ int trace_graph_entry(struct ftrace_graph_ent *trace,
return ret;
}

+int trace_graph_entry(struct ftrace_graph_ent *trace,
+ struct fgraph_ops *gops,
+ struct ftrace_regs *fregs)
+{
+ return graph_entry(trace, gops, NULL);
+}
+
+static int trace_graph_entry_args(struct ftrace_graph_ent *trace,
+ struct fgraph_ops *gops,
+ struct ftrace_regs *fregs)
+{
+ return graph_entry(trace, gops, fregs);
+}
+
static void
__trace_graph_function(struct trace_array *tr,
unsigned long ip, unsigned int trace_ctx)
@@ -423,7 +459,10 @@ static int graph_trace_init(struct trace_array *tr)
{
int ret;

- tr->gops->entryfunc = trace_graph_entry;
+ if (tracer_flags_is_set(TRACE_GRAPH_ARGS))
+ tr->gops->entryfunc = trace_graph_entry_args;
+ else
+ tr->gops->entryfunc = trace_graph_entry;

if (tracing_thresh)
tr->gops->retfunc = trace_graph_thresh_return;
@@ -780,7 +819,7 @@ static void print_graph_retaddr(struct trace_seq *s, struct fgraph_retaddr_ent_e

static void print_graph_retval(struct trace_seq *s, struct ftrace_graph_ent_entry *entry,
struct ftrace_graph_ret *graph_ret, void *func,
- u32 opt_flags, u32 trace_flags)
+ u32 opt_flags, u32 trace_flags, int args_size)
{
unsigned long err_code = 0;
unsigned long retval = 0;
@@ -814,7 +853,14 @@ static void print_graph_retval(struct trace_seq *s, struct ftrace_graph_ent_entr
if (entry->ent.type != TRACE_GRAPH_RETADDR_ENT)
print_retaddr = false;

- trace_seq_printf(s, "%ps();", func);
+ trace_seq_printf(s, "%ps", func);
+
+ if (args_size >= FTRACE_REGS_MAX_ARGS * sizeof(long)) {
+ print_function_args(s, entry->args, (unsigned long)func);
+ trace_seq_putc(s, ';');
+ } else
+ trace_seq_puts(s, "();");
+
if (print_retval || print_retaddr)
trace_seq_puts(s, " /*");
else
@@ -836,12 +882,13 @@ static void print_graph_retval(struct trace_seq *s, struct ftrace_graph_ent_entr
}

if (!entry || print_retval || print_retaddr)
- trace_seq_puts(s, " */\n");
+ trace_seq_puts(s, " */");
}

#else

-#define print_graph_retval(_seq, _ent, _ret, _func, _opt_flags, _trace_flags) do {} while (0)
+#define print_graph_retval(_seq, _ent, _ret, _func, _opt_flags, _trace_flags, args_size) \
+ do {} while (0)

#endif

@@ -857,10 +904,14 @@ print_graph_entry_leaf(struct trace_iterator *iter,
struct ftrace_graph_ret *graph_ret;
struct ftrace_graph_ent *call;
unsigned long long duration;
+ unsigned long ret_func;
unsigned long func;
+ int args_size;
int cpu = iter->cpu;
int i;

+ args_size = iter->ent_size - offsetof(struct ftrace_graph_ent_entry, args);
+
graph_ret = &ret_entry->ret;
call = &entry->graph_ent;
duration = graph_ret->rettime - graph_ret->calltime;
@@ -892,16 +943,25 @@ print_graph_entry_leaf(struct trace_iterator *iter,
for (i = 0; i < call->depth * TRACE_GRAPH_INDENT; i++)
trace_seq_putc(s, ' ');

+ ret_func = graph_ret->func + iter->tr->text_delta;
+
/*
* Write out the function return value or return address
*/
if (flags & (__TRACE_GRAPH_PRINT_RETVAL | __TRACE_GRAPH_PRINT_RETADDR)) {
print_graph_retval(s, entry, graph_ret,
(void *)graph_ret->func + iter->tr->text_delta,
- flags, tr->trace_flags);
+ flags, tr->trace_flags, args_size);
} else {
- trace_seq_printf(s, "%ps();\n", (void *)func);
+ trace_seq_printf(s, "%ps", (void *)ret_func);
+
+ if (args_size >= FTRACE_REGS_MAX_ARGS * sizeof(long)) {
+ print_function_args(s, entry->args, ret_func);
+ trace_seq_putc(s, ';');
+ } else
+ trace_seq_puts(s, "();");
}
+ trace_seq_printf(s, "\n");

print_graph_irq(iter, graph_ret->func, TRACE_GRAPH_RET,
cpu, iter->ent->pid, flags);
@@ -918,6 +978,7 @@ print_graph_entry_nested(struct trace_iterator *iter,
struct fgraph_data *data = iter->private;
struct trace_array *tr = iter->tr;
unsigned long func;
+ int args_size;
int i;

if (data) {
@@ -942,7 +1003,17 @@ print_graph_entry_nested(struct trace_iterator *iter,

func = call->func + iter->tr->text_delta;

- trace_seq_printf(s, "%ps() {", (void *)func);
+ trace_seq_printf(s, "%ps", (void *)func);
+
+ args_size = iter->ent_size - offsetof(struct ftrace_graph_ent_entry, args);
+
+ if (args_size >= FTRACE_REGS_MAX_ARGS * sizeof(long))
+ print_function_args(s, entry->args, func);
+ else
+ trace_seq_puts(s, "()");
+
+ trace_seq_puts(s, " {");
+
if (flags & __TRACE_GRAPH_PRINT_RETADDR &&
entry->ent.type == TRACE_GRAPH_RETADDR_ENT)
print_graph_retaddr(s, (struct fgraph_retaddr_ent_entry *)entry,
@@ -1112,21 +1183,38 @@ print_graph_entry(struct ftrace_graph_ent_entry *field, struct trace_seq *s,
struct trace_iterator *iter, u32 flags)
{
struct fgraph_data *data = iter->private;
- struct ftrace_graph_ent *call = &field->graph_ent;
+ struct ftrace_graph_ent *call;
struct ftrace_graph_ret_entry *leaf_ret;
static enum print_line_t ret;
int cpu = iter->cpu;
+ /*
+ * print_graph_entry() may consume the current event,
+ * thus @field may become invalid, so we need to save it.
+ * sizeof(struct ftrace_graph_ent_entry) is very small,
+ * it can be safely saved at the stack.
+ */
+ struct ftrace_graph_ent_entry *entry;
+ u8 save_buf[sizeof(*entry) + FTRACE_REGS_MAX_ARGS * sizeof(long)];
+
+ /* The ent_size is expected to be as big as the entry */
+ if (iter->ent_size > sizeof(save_buf))
+ iter->ent_size = sizeof(save_buf);
+
+ entry = (void *)save_buf;
+ memcpy(entry, field, iter->ent_size);
+
+ call = &entry->graph_ent;

if (check_irq_entry(iter, flags, call->func, call->depth))
return TRACE_TYPE_HANDLED;

print_graph_prologue(iter, s, TRACE_GRAPH_ENT, call->func, flags);

- leaf_ret = get_return_for_leaf(iter, field);
+ leaf_ret = get_return_for_leaf(iter, entry);
if (leaf_ret)
- ret = print_graph_entry_leaf(iter, field, leaf_ret, s, flags);
+ ret = print_graph_entry_leaf(iter, entry, leaf_ret, s, flags);
else
- ret = print_graph_entry_nested(iter, field, s, cpu, flags);
+ ret = print_graph_entry_nested(iter, entry, s, cpu, flags);

if (data) {
/*
@@ -1197,7 +1285,8 @@ print_graph_return(struct ftrace_graph_ret *trace, struct trace_seq *s,
* funcgraph-retval option is enabled.
*/
if (flags & __TRACE_GRAPH_PRINT_RETVAL) {
- print_graph_retval(s, NULL, trace, (void *)func, flags, tr->trace_flags);
+ print_graph_retval(s, NULL, trace, (void *)func, flags,
+ tr->trace_flags, 0);
} else {
/*
* If the return function does not have a matching entry,
@@ -1325,16 +1414,8 @@ print_graph_function_flags(struct trace_iterator *iter, u32 flags)

switch (entry->type) {
case TRACE_GRAPH_ENT: {
- /*
- * print_graph_entry() may consume the current event,
- * thus @field may become invalid, so we need to save it.
- * sizeof(struct ftrace_graph_ent_entry) is very small,
- * it can be safely saved at the stack.
- */
- struct ftrace_graph_ent_entry saved;
trace_assign_type(field, entry);
- saved = *field;
- return print_graph_entry(&saved, s, iter, flags);
+ return print_graph_entry(field, s, iter, flags);
}
#ifdef CONFIG_FUNCTION_GRAPH_RETADDR
case TRACE_GRAPH_RETADDR_ENT: {
--
2.45.2