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Diffstat (limited to 'include/linux/trace_printk.h')
| -rw-r--r-- | include/linux/trace_printk.h | 203 |
1 files changed, 203 insertions, 0 deletions
diff --git a/include/linux/trace_printk.h b/include/linux/trace_printk.h new file mode 100644 index 000000000000..2670ec7f4262 --- /dev/null +++ b/include/linux/trace_printk.h @@ -0,0 +1,203 @@ +/* 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 |