include/linux/trace_printk.h

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_TRACE_PRINTK_H
#define _LINUX_TRACE_PRINTK_H

#include <linux/compiler_attributes.h>
#include <linux/instruction_pointer.h>
#include <linux/stddef.h>
#include <linux/stringify.h>

/*
 * General tracing related utility functions - trace_printk(),
 * tracing_on/tracing_off and tracing_start()/tracing_stop
 *
 * Use tracing_on/tracing_off when you want to quickly turn on or off
 * tracing. It simply enables or disables the recording of the trace events.
 * This also corresponds to the user space /sys/kernel/tracing/tracing_on
 * file, which gives a means for the kernel and userspace to interact.
 * Place a tracing_off() in the kernel where you want tracing to end.
 * From user space, examine the trace, and then echo 1 > tracing_on
 * to continue tracing.
 *
 * tracing_stop/tracing_start has slightly more overhead. It is used
 * by things like suspend to ram where disabling the recording of the
 * trace is not enough, but tracing must actually stop because things
 * like calling smp_processor_id() may crash the system.
 *
 * Most likely, you want to use tracing_on/tracing_off.
 */

enum ftrace_dump_mode {
	DUMP_NONE,
	DUMP_ALL,
	DUMP_ORIG,
	DUMP_PARAM,
};

#ifdef CONFIG_TRACING
void tracing_on(void);
void tracing_off(void);
int tracing_is_on(void);
void tracing_snapshot(void);
void tracing_snapshot_alloc(void);

extern void tracing_start(void);
extern void tracing_stop(void);

static inline __printf(1, 2)
void ____trace_printk_check_format(const char *fmt, ...)
{
}
#define __trace_printk_check_format(fmt, args...)			\
do {									\
	if (0)								\
		____trace_printk_check_format(fmt, ##args);		\
} while (0)

/**
 * trace_printk - printf formatting in the ftrace buffer
 * @fmt: the printf format for printing
 *
 * Note: __trace_printk is an internal function for trace_printk() and
 *       the @ip is passed in via the trace_printk() macro.
 *
 * This function allows a kernel developer to debug fast path sections
 * that printk is not appropriate for. By scattering in various
 * printk like tracing in the code, a developer can quickly see
 * where problems are occurring.
 *
 * This is intended as a debugging tool for the developer only.
 * Please refrain from leaving trace_printks scattered around in
 * your code. (Extra memory is used for special buffers that are
 * allocated when trace_printk() is used.)
 *
 * A little optimization trick is done here. If there's only one
 * argument, there's no need to scan the string for printf formats.
 * The trace_puts() will suffice. But how can we take advantage of
 * using trace_puts() when trace_printk() has only one argument?
 * By stringifying the args and checking the size we can tell
 * whether or not there are args. __stringify((__VA_ARGS__)) will
 * turn into "()\0" with a size of 3 when there are no args, anything
 * else will be bigger. All we need to do is define a string to this,
 * and then take its size and compare to 3. If it's bigger, use
 * do_trace_printk() otherwise, optimize it to trace_puts(). Then just
 * let gcc optimize the rest.
 */

#define trace_printk(fmt, ...)				\
do {							\
	char _______STR[] = __stringify((__VA_ARGS__));	\
	if (sizeof(_______STR) > 3)			\
		do_trace_printk(fmt, ##__VA_ARGS__);	\
	else						\
		trace_puts(fmt);			\
} while (0)

#define do_trace_printk(fmt, args...)					\
do {									\
	static const char *trace_printk_fmt __used			\
		__section("__trace_printk_fmt") =			\
		__builtin_constant_p(fmt) ? fmt : NULL;			\
									\
	__trace_printk_check_format(fmt, ##args);			\
									\
	if (__builtin_constant_p(fmt))					\
		__trace_bprintk(_THIS_IP_, trace_printk_fmt, ##args);	\
	else								\
		__trace_printk(_THIS_IP_, fmt, ##args);			\
} while (0)

int __trace_bprintk(unsigned long ip, const char *fmt, ...);

extern __printf(2, 3)
int __trace_printk(unsigned long ip, const char *fmt, ...);

/**
 * trace_puts - write a string into the ftrace buffer
 * @str: the string to record
 *
 * Note: __trace_bputs is an internal function for trace_puts and
 *       the @ip is passed in via the trace_puts macro.
 *
 * This is similar to trace_printk() but is made for those really fast
 * paths that a developer wants the least amount of "Heisenbug" effects,
 * where the processing of the print format is still too much.
 *
 * This function allows a kernel developer to debug fast path sections
 * that printk is not appropriate for. By scattering in various
 * printk like tracing in the code, a developer can quickly see
 * where problems are occurring.
 *
 * This is intended as a debugging tool for the developer only.
 * Please refrain from leaving trace_puts scattered around in
 * your code. (Extra memory is used for special buffers that are
 * allocated when trace_puts() is used.)
 *
 * Returns: 0 if nothing was written, positive # if string was.
 *  (1 when __trace_bputs is used, strlen(str) when __trace_puts is used)
 */

#define trace_puts(str) ({						\
	static const char *trace_printk_fmt __used			\
		__section("__trace_printk_fmt") =			\
		__builtin_constant_p(str) ? str : NULL;			\
									\
	if (__builtin_constant_p(str))					\
		__trace_bputs(_THIS_IP_, trace_printk_fmt);		\
	else								\
		__trace_puts(_THIS_IP_, str);				\
})
extern int __trace_bputs(unsigned long ip, const char *str);
extern int __trace_puts(unsigned long ip, const char *str);

extern void trace_dump_stack(int skip);

/*
 * The double __builtin_constant_p is because gcc will give us an error
 * if we try to allocate the static variable to fmt if it is not a
 * constant. Even with the outer if statement.
 */
#define ftrace_vprintk(fmt, vargs)					\
do {									\
	if (__builtin_constant_p(fmt)) {				\
		static const char *trace_printk_fmt __used		\
		  __section("__trace_printk_fmt") =			\
			__builtin_constant_p(fmt) ? fmt : NULL;		\
									\
		__ftrace_vbprintk(_THIS_IP_, trace_printk_fmt, vargs);	\
	} else								\
		__ftrace_vprintk(_THIS_IP_, fmt, vargs);		\
} while (0)

extern __printf(2, 0) int
__ftrace_vbprintk(unsigned long ip, const char *fmt, va_list ap);

extern __printf(2, 0) int
__ftrace_vprintk(unsigned long ip, const char *fmt, va_list ap);

extern void ftrace_dump(enum ftrace_dump_mode oops_dump_mode);
#else
static inline void tracing_start(void) { }
static inline void tracing_stop(void) { }
static inline void trace_dump_stack(int skip) { }

static inline void tracing_on(void) { }
static inline void tracing_off(void) { }
static inline int tracing_is_on(void) { return 0; }
static inline void tracing_snapshot(void) { }
static inline void tracing_snapshot_alloc(void) { }

static inline __printf(1, 2)
int trace_printk(const char *fmt, ...)
{
	return 0;
}
static __printf(1, 0) inline int
ftrace_vprintk(const char *fmt, va_list ap)
{
	return 0;
}
static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
#endif /* CONFIG_TRACING */

#endif