--- name: "tep_parse_saved_cmdlines" section: "3" platform: "linux" package: "libtraceevent" version: "1:1.9.1-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/tep_parse_saved_cmdlines" --- # tep\_parse\_saved\_cmdlines(3) Parsing functions to load mappings ## NAME tep\_parse\_saved\_cmdlines, tep\_parse\_printk\_formats, tep\_parse\_kallsyms, tep\_parse\_last\_boot\_info, tep\_load\_modules - Parsing functions to load mappings ## SYNOPSIS ``` #include int tep_parse_saved_cmdlines(struct tep_handle *tep, const char *buf); int tep_parse_printk_formats(struct tep_handle *tep, const char *buf); int tep_parse_kallsyms(struct tep_handle *tep, const char *buf); int tep_parse_last_boot_info(struct tep_handle *tep, const char *lbi); int tep_load_modules(struct tep_handle *tep, char *modules, size_t size); ``` ## DESCRIPTION **tep\_parse\_saved\_cmdlines()** is a helper function to parse content in the tracefs file system of the "saved\_cmdlines" file (stored in a string buffer passed in by *buf*) and loads the mapping of the process IDs (pid) to the comm names in the *tep* handler. The events store the pid and this is used to be able to show the process names associated to those process ids. It parses the string *buf* that holds the content of saved\_cmdlines and ends with a nul character (*\\0*). **tep\_parse\_printk\_formats()** is a helper function to parse content in the tracefs file system of the "printk\_formats" file (stored in a string buffer passed in by *buf*) and loads the mapping of addresses of strings that may be referenced by events. Events only store the address of constant strings in the kernel, and the mapping of their address to the string is exported to user space in the printk\_formats file. It parses the string *buf* that holds the content of printk\_formats and ends with a nul character (*\\0*). **tep\_parse\_kallsyms()** is a helper function to parse the Linux kernel /proc/kallsyms format (stored in a string buffer passed in by *buf*) and load the functions into the *tep* handler such that function IP addresses can be mapped to their name when parsing events with %pS in the print format field. It parses the string *buf* that holds the content of /proc/kallsyms and ends with a nul character (*\\0*). **tep\_parse\_last\_boot\_info()** loads information from the last\_boot\_info file of a persistent ring buffer instance. If a tracefs instance is declared as a persistent ring buffer and contains data from a previous boot, the last\_boot\_info file will have the addresses of the kernel as well as modules. It will use this information to base the function offsets in the binary buffer to match the function offsets in the kallsyms (loaded by **tep\_parse\_kallsyms()**) into the *tep* handler. The *lbi* is a nul terminated string that contains the content of the last\_boot\_info file from the persistent ring buffer instance. **tep\_load\_modules()** loads the contents of the file /proc/modules into the *tep* handler. This will be used to match the modules found in the last\_boot\_info (loaded by **tep\_parse\_last\_boot\_info()**) to match the offsets of the binary data in in a persistent ring buffer that matches the address of a module from the previous boot to a module address found in *modules*. The *modules* parameter does not need to be nul terminated, but *size* is used to denote the size of the *modules* string. This function is useless if **tep\_parse\_last\_boot\_info()** isnt used. ## RETURN VALUE The **tep\_parse\_saved\_cmdlines**() function returns 0 in case of success, or -1 in case of an error. The **tep\_parse\_printk\_formats**() function returns 0 in case of success, or -1 in case of an error. The **tep\_parse\_kallsyms**() function returns 0 in case of success, or -1 in case of an error. The **tep\_parse\_last\_boot\_info**() function retuns 0 in case of success, or -1 in case of error. The **tep\_load\_modules**() function returns 0 in case of success, or -1 in case of error. ## EXAMPLE ``` ... #include #include #include int load_cmdlines(struct tep_handle *tep) { char *buf = NULL; int r; buf = tracefs_instance_file_read(NULL, "saved_cmdlines", NULL); if (!buf) return -1; r = tep_parse_saved_cmdlines(tep, buf); free(buf); return r; } int load_print_strings(struct tep_handle *tep) { char *buf = NULL; int r; buf = tracefs_instance_file_read(NULL, "printk_formats", NULL); if (!buf) return -1; r = tep_parse_printk_formats(tep, buf); free(buf); return r; } static char *read_file(const char *file, size_t *size) { FILE *fp; char *line = NULL; char *buf = NULL; size_t sz = 0; size_t len = 0; int r; fp = fopen(file, "r"); while ((r = getline(&line, &sz, fp)) >= 0) { buf = realloc(buf, len + r + 1); memcpy(buf + len, line, r); len += r; } free(line); fclose(fp); if (!buf) return NULL; buf[len] = 0; *size = len; return buf; } int load_kallsyms(struct tep_handle *tep) { char *buf; size_t sz; int r; buf = read_file("/proc/kallsyms", &sz); if (!buf) return -1; r = tep_parse_kallsyms(tep, buf); free(buf); return r; } int load_last_boot(struct tep_handle *tep, struct tracefs_instance *instance) { char *buf; size_t sz; int r; buf = tracefs_instance_file_read(instance, "last_boot_info", NULL); if (!buf) return 0; r = tep_parse_last_boot_info(tep, buf); free(buf); if (r < 0) return r; buf = read_file("/proc/modules", &sz); if (!buf) return -1; r = tep_parse_kallsyms(tep, buf); free(buf); return r; } ... ``` ## FILES ``` event-parse.h Header file to include in order to have access to the library APIs. -ltraceevent Linker switch to add when building a program that uses the library. ``` ## SEE ALSO [**libtraceevent**(3)](/libtraceevent/3.md), [**trace-cmd**(1)](/trace-cmd/1.md), [**tep\_register\_comm**(3)](/tep_register_comm/3.md), [**tep\_register\_function**(3)](/tep_register_function/3.md), [**tep\_register\_print\_string**(3)](/tep_register_print_string/3.md) ## AUTHOR ``` Steven Rostedt , author of libtraceevent. Tzvetomir Stoyanov , coauthor of libtraceevent. ``` ## REPORTING BUGS Report bugs to \<**linux-trace-devel@vger.kernel.org**\[3\]\> ## LICENSE libtraceevent is Free Software licensed under the GNU LGPL 2.1 ## RESOURCES **https://git.kernel.org/pub/scm/libs/libtrace/libtraceevent.git/** ## NOTES - 1\. rostedt@goodmis.org mailto:rostedt@goodmis.org - 2\. tz.stoyanov@gmail.com mailto:tz.stoyanov@gmail.com - 3\. linux-trace-devel@vger.kernel.org mailto:linux-trace-devel@vger.kernel.org