Re: [PATCH v2 2/4] ftrace: Add support for function argument to graph tracer

Masami Hiramatsu
2024-12-25T15:41:58Z

On Mon, 23 Dec 2024 15:13:49 -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 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>

Do we need these headers? I think it is wrapped by print_function_args().

>
> #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, " */");

Do we need this change?

Thank you,

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