# libtraceevent(3) Manual Page

## NAME

tep_find_function, tep_find_function_address, tep_set_function_resolver, tep_reset_function_resolver, tep_register_function, tep_register_print_string - function related tep APIs

## SYNOPSIS

    #include <event-parse.h>

    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);
    const char *tep_find_function(struct tep_handle *tep, unsigned long long addr);
    unsigned long long tep_find_function_address(struct tep_handle *tep, unsigned long long addr);
    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);

## 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(), tep_find_function_address(), 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_find_function() function returns the function name, which contains the given address addr. The tep argument is the trace event parser context.

The tep_find_function_address() function returns the function start address, by given address addr. The addr does not have to be exact, it will select the function that would contain it. The tep argument is the trace event parser context.

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.

## RETURN VALUE

The tep_set_function_resolver() function returns 0 in case of success, or -1 in case of an error.

The tep_find_function() function returns the function name, or NULL in case it cannot be found.

The tep_find_function_address() function returns the function start address, or 0 in case it cannot be found.

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 <event-parse.h>
    ...
    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), trace-cmd(1)

## AUTHOR

    Steven Rostedt <rostedt@goodmis.org>, author of libtraceevent.
    Tzvetomir Stoyanov <tz.stoyanov@gmail.com>, author of this man page.

## REPORTING BUGS

Report bugs to <linux-trace-devel@vger.kernel.org>

## LICENSE

libtraceevent is Free Software licensed under the GNU LGPL 2.1

## RESOURCES

https://git.kernel.org/pub/scm/libs/libtrace/libtraceevent.git/