Commit 533c20b0 authored by Sven Schnelle's avatar Sven Schnelle Committed by Steven Rostedt (Google)
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ftrace: Add print_function_args() 

Add a function to decode argument types with the help of BTF. Will
be used to display arguments in the function and function graph
tracer.

It can only handle simply arguments and up to FTRACE_REGS_MAX_ARGS number
of arguments. When it hits a max, it will print ", ...":

   page_to_skb(vi=0xffff8d53842dc980, rq=0xffff8d53843a0800, page=0xfffffc2e04337c00, offset=6160, len=64, truesize=1536, ...)

And if it hits an argument that is not recognized, it will print the raw
value and the type of argument it is:

   make_vfsuid(idmap=0xffffffff87f99db8, fs_userns=0xffffffff87e543c0, kuid=0x0 (STRUCT))
   __pti_set_user_pgtbl(pgdp=0xffff8d5384ab47f8, pgd=0x110e74067 (STRUCT))

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Guo Ren <guoren@kernel.org>
Cc: Donglin Peng <dolinux.peng@gmail.com>
Cc: Zheng Yejian <zhengyejian@huaweicloud.com>
Link: https://lore.kernel.org/20250227185822.639418500@goodmis.org


Reviewed-by: default avatarMasami Hiramatsu (Google) <mhiramat@kernel.org>
Co-developed-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: default avatarSven Schnelle <svens@linux.ibm.com>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 0c667775

include/linux/ftrace_regs.h

+5 −0
Original line number Diff line number Diff line
@@ -35,4 +35,9 @@ struct ftrace_regs; 


#endif /* HAVE_ARCH_FTRACE_REGS */



/* This can be overridden by the architectures */

#ifndef FTRACE_REGS_MAX_ARGS

# define FTRACE_REGS_MAX_ARGS	6

#endif



#endif /* _LINUX_FTRACE_REGS_H */

kernel/trace/Kconfig

+6 −0
Original line number Diff line number Diff line
@@ -263,6 +263,12 @@ config FUNCTION_GRAPH_RETADDR 
	  the function is called. This feature is off by default, and you can

	  enable it via the trace option funcgraph-retaddr.



config FUNCTION_TRACE_ARGS

       bool

	depends on HAVE_FUNCTION_ARG_ACCESS_API

	depends on DEBUG_INFO_BTF

	default y



config DYNAMIC_FTRACE

	bool "enable/disable function tracing dynamically"

	depends on FUNCTION_TRACER

kernel/trace/trace_output.c

+85 −0
Original line number Diff line number Diff line
@@ -12,8 +12,11 @@ 
#include <linux/sched/clock.h>

#include <linux/sched/mm.h>

#include <linux/idr.h>

#include <linux/btf.h>

#include <linux/bpf.h>



#include "trace_output.h"

#include "trace_btf.h"



/* must be a power of 2 */

#define EVENT_HASHSIZE	128
@@ -684,6 +687,88 @@ int trace_print_lat_context(struct trace_iterator *iter) 
	return !trace_seq_has_overflowed(s);

}



#ifdef CONFIG_FUNCTION_TRACE_ARGS

void print_function_args(struct trace_seq *s, unsigned long *args,

			 unsigned long func)

{

	const struct btf_param *param;

	const struct btf_type *t;

	const char *param_name;

	char name[KSYM_NAME_LEN];

	unsigned long arg;

	struct btf *btf;

	s32 tid, nr = 0;

	int a, p, x;



	trace_seq_printf(s, "(");



	if (!args)

		goto out;

	if (lookup_symbol_name(func, name))

		goto out;



	/* TODO: Pass module name here too */

	t = btf_find_func_proto(name, &btf);

	if (IS_ERR_OR_NULL(t))

		goto out;



	param = btf_get_func_param(t, &nr);

	if (!param)

		goto out_put;



	for (a = 0, p = 0; p < nr; a++, p++) {

		if (p)

			trace_seq_puts(s, ", ");



		/* This only prints what the arch allows (6 args by default) */

		if (a == FTRACE_REGS_MAX_ARGS) {

			trace_seq_puts(s, "...");

			break;

		}



		arg = args[a];



		param_name = btf_name_by_offset(btf, param[p].name_off);

		if (param_name)

			trace_seq_printf(s, "%s=", param_name);

		t = btf_type_skip_modifiers(btf, param[p].type, &tid);



		switch (t ? BTF_INFO_KIND(t->info) : BTF_KIND_UNKN) {

		case BTF_KIND_UNKN:

			trace_seq_putc(s, '?');

			/* Still print unknown type values */

			fallthrough;

		case BTF_KIND_PTR:

			trace_seq_printf(s, "0x%lx", arg);

			break;

		case BTF_KIND_INT:

			trace_seq_printf(s, "%ld", arg);

			break;

		case BTF_KIND_ENUM:

			trace_seq_printf(s, "%ld", arg);

			break;

		default:

			/* This does not handle complex arguments */

			trace_seq_printf(s, "(%s)[0x%lx", btf_type_str(t), arg);

			for (x = sizeof(long); x < t->size; x += sizeof(long)) {

				trace_seq_putc(s, ':');

				if (++a == FTRACE_REGS_MAX_ARGS) {

					trace_seq_puts(s, "...]");

					goto out_put;

				}

				trace_seq_printf(s, "0x%lx", args[a]);

			}

			trace_seq_putc(s, ']');

			break;

		}

	}

out_put:

	btf_put(btf);

out:

	trace_seq_printf(s, ")");

}

#endif



/**

 * ftrace_find_event - find a registered event

 * @type: the type of event to look for

kernel/trace/trace_output.h

+9 −0
Original line number Diff line number Diff line
@@ -41,5 +41,14 @@ extern struct rw_semaphore trace_event_sem; 
#define SEQ_PUT_HEX_FIELD(s, x)				\

	trace_seq_putmem_hex(s, &(x), sizeof(x))



#ifdef CONFIG_FUNCTION_TRACE_ARGS

void print_function_args(struct trace_seq *s, unsigned long *args,

			 unsigned long func);

#else

static inline void print_function_args(struct trace_seq *s, unsigned long *args,

				       unsigned long func) {

	trace_seq_puts(s, "()");

}

#endif

#endif