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ftrace: Add print_function_args()

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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: 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>
This commit is contained in:
Sven Schnelle 2025-02-27 13:58:05 -05:00 • committed by Steven Rostedt (Google)
parent 0c667775fe
commit 533c20b062
4 changed files with 105 additions and 0 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

5
include/linux/ftrace_regs.h
View file

@ -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 */

6
kernel/trace/Kconfig
View file

@ -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

85
kernel/trace/trace_output.c
View file

@ -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

9
kernel/trace/trace_output.h
View file

@ -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