diff options
Diffstat (limited to 'include')
| -rw-r--r-- | include/asm-generic/vmlinux.lds.h | 7 | ||||
| -rw-r--r-- | include/linux/ftrace_event.h | 34 |
2 files changed, 40 insertions, 1 deletions
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 69732d2..83e2c31 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -122,8 +122,12 @@ #define TRACE_PRINTKS() VMLINUX_SYMBOL(__start___trace_bprintk_fmt) = .; \ *(__trace_printk_fmt) /* Trace_printk fmt' pointer */ \ VMLINUX_SYMBOL(__stop___trace_bprintk_fmt) = .; +#define TRACEPOINT_STR() VMLINUX_SYMBOL(__start___tracepoint_str) = .; \ + *(__tracepoint_str) /* Trace_printk fmt' pointer */ \ + VMLINUX_SYMBOL(__stop___tracepoint_str) = .; #else #define TRACE_PRINTKS() +#define TRACEPOINT_STR() #endif #ifdef CONFIG_FTRACE_SYSCALLS @@ -190,7 +194,8 @@ VMLINUX_SYMBOL(__stop___verbose) = .; \ LIKELY_PROFILE() \ BRANCH_PROFILE() \ - TRACE_PRINTKS() + TRACE_PRINTKS() \ + TRACEPOINT_STR() /* * Data section helpers diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h index 4372658..81af18a 100644 --- a/include/linux/ftrace_event.h +++ b/include/linux/ftrace_event.h @@ -357,6 +357,40 @@ do { \ __trace_printk(ip, fmt, ##args); \ } while (0) +/** + * tracepoint_string - register constant persistent string to trace system + * @str - a constant persistent string that will be referenced in tracepoints + * + * If constant strings are being used in tracepoints, it is faster and + * more efficient to just save the pointer to the string and reference + * that with a printf "%s" instead of saving the string in the ring buffer + * and wasting space and time. + * + * The problem with the above approach is that userspace tools that read + * the binary output of the trace buffers do not have access to the string. + * Instead they just show the address of the string which is not very + * useful to users. + * + * With tracepoint_string(), the string will be registered to the tracing + * system and exported to userspace via the debugfs/tracing/printk_formats + * file that maps the string address to the string text. This way userspace + * tools that read the binary buffers have a way to map the pointers to + * the ASCII strings they represent. + * + * The @str used must be a constant string and persistent as it would not + * make sense to show a string that no longer exists. But it is still fine + * to be used with modules, because when modules are unloaded, if they + * had tracepoints, the ring buffers are cleared too. As long as the string + * does not change during the life of the module, it is fine to use + * tracepoint_string() within a module. + */ +#define tracepoint_string(str) \ + ({ \ + static const char *___tp_str __tracepoint_string = str; \ + ___tp_str; \ + }) +#define __tracepoint_string __attribute__((section("__tracepoint_str"))) + #ifdef CONFIG_PERF_EVENTS struct perf_event; |