--- name: "tep_register_print_string" section: "3" platform: "linux" package: "libtraceevent-doc" version: "1:1.8.4-2" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/tep_set_function_resolver" --- # tep\_register\_print\_string(3) function related tep APIs Part of [tep\_set\_function\_resolver(3)](/tep_set_function_resolver/3.md). ## NAME tep\_set\_function\_resolver, tep\_reset\_function\_resolver, tep\_register\_function, tep\_register\_print\_string, tep\_get\_function\_count - function related tep APIs ## SYNOPSIS ``` #include typedef char *(tep_func_resolver_t)(void *priv, unsigned long long *addrp, char **modp); int tep_set_function_resolver(struct tep_handle *tep, tep_func_resolver_t *func, void *priv); void tep_reset_function_resolver(struct tep_handle *tep); int tep_register_function(struct tep_handle *tep, char *name, unsigned long long addr, char *mod); int tep_register_print_string(struct tep_handle *tep, const char *fmt, unsigned long long addr); int tep_get_function_count(struct tep_handle *tep) ``` ## DESCRIPTION Some tools may have already a way to resolve the kernel functions. These APIs allow them to keep using it instead of duplicating all the entries inside. The *tep\_func\_resolver\_t* type is the prototype of the alternative kernel functions resolver. This function receives a pointer to its custom context (set with the **tep\_set\_function\_resolver()** call ) and the address of a kernel function, which has to be resolved. In case of success, it should return the name of the function and its module (if any) in *modp*. The **tep\_set\_function\_resolver()** function registers *func* as an alternative kernel functions resolver. The *tep* argument is trace event parser context. The *priv* argument is a custom context of the *func* function. The function resolver is used by the APIs [**tep\_find\_function**(3)](/tep_find_function/3.md), [**tep\_find\_function\_address**(3)](/tep_find_function_address/3.md), and **tep\_print\_func\_field()** to resolve a function address to a function name. The **tep\_reset\_function\_resolver()** function resets the kernel functions resolver to the default function. The *tep* argument is trace event parser context. These APIs can be used to find function name and start address, by given address. The given address does not have to be exact, it will select the function that would contain it. The **tep\_register\_function()** function registers a function name mapped to an address and (optional) module. This mapping is used in case the function tracer or events have "%pS" parameter in its format string. It is common to pass in the kallsyms function names with their corresponding addresses with this function. The *tep* argument is the trace event parser context. The *name* is the name of the function, the string is copied internally. The *addr* is the start address of the function. The *mod* is the kernel module the function may be in (NULL for none). The **tep\_register\_print\_string()** function registers a string by the address it was stored in the kernel. Some strings internal to the kernel with static address are passed to certain events. The "%s" in the event’s format field which has an address needs to know what string would be at that address. The tep\_register\_print\_string() supplies the parsing with the mapping between kernel addresses and those strings. The *tep* argument is the trace event parser context. The *fmt* is the string to register, it is copied internally. The *addr* is the address the string was located at. **tep\_get\_function\_count**() returns the number of registered functions in a tep handler. ## RETURN VALUE The **tep\_set\_function\_resolver()** function returns 0 in case of success, or -1 in case of an error. The **tep\_register\_function()** function returns 0 in case of success. In case of an error -1 is returned, and errno is set to the appropriate error number. The **tep\_register\_print\_string()** function returns 0 in case of success. In case of an error -1 is returned, and errno is set to the appropriate error number. ## EXAMPLE ``` #include ... struct tep_handle *tep = tep_alloc(); ... char *my_resolve_kernel_addr(void *context, unsigned long long *addrp, char **modp) { struct db *function_database = context; struct symbol *sym = sql_lookup(function_database, *addrp); if (!sym) return NULL; *modp = sym->module_name; return sym->name; } void show_function( unsigned long long addr) { unsigned long long fstart; const char *fname; if (tep_set_function_resolver(tep, my_resolve_kernel_addr, function_database) != 0) { /* failed to register my_resolve_kernel_addr */ } /* These APIs use my_resolve_kernel_addr() to resolve the addr */ fname = tep_find_function(tep, addr); fstart = tep_find_function_address(tep, addr); /* addr is in function named fname, starting at fstart address, at offset (addr - fstart) */ tep_reset_function_resolver(tep); } ... if (tep_register_function(tep, "kvm_exit", (unsigned long long) 0x12345678, "kvm") != 0) { /* Failed to register kvm_exit address mapping */ } ... if (tep_register_print_string(tep, "print string", (unsigned long long) 0x87654321, NULL) != 0) { /* Failed to register "print string" address mapping */ } ... ``` ## 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) ## AUTHOR ``` Steven Rostedt , author of libtraceevent. Tzvetomir Stoyanov , author of this man page. ``` ## 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