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DLINFO(3) Library Functions Manual DLINFO(3) NAME dlinfo -- information about dynamically loaded object LIBRARY Standard C Library (libc, -lc) SYNOPSIS #include <link.h> #include <dlfcn.h> int dlinfo(void * restrict handle, int request, void * restrict p); DESCRIPTION The dlinfo() function provides information about dynamically loaded ob- ject. The action taken by dlinfo() and exact meaning and type of p ar- gument depend on value of the request argument provided by caller. The handle argument is either the value returned from the dlopen(3) function call or special handle RTLD_SELF. If handle is the value re- turned from dlopen(3), the information returned by the dlinfo() func- tion pertains to the specified object. If handle is the special handle RTLD_SELF, the information returned pertains to the caller itself. Possible values for the request argument are: RTLD_DI_LINKMAP Retrieve the Link_map (struct link_map) structure pointer for the specified handle. On successful return, the p argument is filled with the pointer to the Link_map structure (Link_map **p) describing a shared object specified by the handle argu- ment. The Link_map structures are maintained as a doubly linked list by ld.so(1), in the same order as dlopen(3) and dlclose(3) are called. See "EXAMPLES", example 1. The Link_map structure is defined in <link.h> and has the fol- lowing members: caddr_t l_addr; /* Base Address of library */ const char *l_name; /* Absolute Path to Library */ const void *l_ld; /* Pointer to .dynamic in memory */ struct link_map *l_next, /* linked list of mapped libs */ *l_prev; l_addr The base address of the object loaded into memory. l_name The full name of the loaded shared object. l_ld The address of the dynamic linking information segment (PT_DYNAMIC) loaded into memory. l_next The next Link_map structure on the link-map list. l_prev The previous Link_map structure on the link-map list. RTLD_DI_SERINFO Retrieve the library search paths associated with the given handle argument. The p argument should point to Dl_serinfo structure buffer (Dl_serinfo *p). The Dl_serinfo structure must be initialized first with the RTLD_DI_SERINFOSIZE request. The returned Dl_serinfo structure contains dls_cnt Dl_serpath entries. Each entry's dlp_name field points to the search path. The corresponding dlp_info field contains one of more flags indicating the origin of the path (see the LA_SER_* flags defined in the <link.h> header file). See "EXAMPLES", example 2, for a usage example. RTLD_DI_SERINFOSIZE Initialize a Dl_serinfo structure for use in a RTLD_DI_SERINFO request. Both the dls_cnt and dls_size fields are returned to indicate the number of search paths applicable to the handle, and the total size of a Dl_serinfo buffer required to hold dls_cnt Dl_serpath entries and the associated search path strings. See "EXAMPLES", example 2, for a usage example. RTLD_DI_ORIGIN Retrieve the origin of the dynamic object associated with the handle. On successful return, p argument is filled with the char pointer (char *p). RETURN VALUES The dlinfo() function returns 0 on success, or -1 if an error occurred. Whenever an error has been detected, a message detailing it can be re- trieved via a call to dlerror(3). EXAMPLES Example 1: Using dlinfo() to retrieve Link_map structure. The following example shows how dynamic library can detect the list of shared libraries loaded after caller's one. For simplicity, error checking has been omitted. Link_map *map; dlinfo(RTLD_SELF, RTLD_DI_LINKMAP, &map); while (map != NULL) { printf("%p: %s\n", map->l_addr, map->l_name); map = map->l_next; } Example 2: Using dlinfo() to retrieve the library search paths. The following example shows how a dynamic object can inspect the li- brary search paths that would be used to locate a simple filename with dlopen(3). For simplicity, error checking has been omitted. Dl_serinfo _info, *info = &_info; Dl_serpath *path; unsigned int cnt; /* determine search path count and required buffer size */ dlinfo(RTLD_SELF, RTLD_DI_SERINFOSIZE, (void *)info); /* allocate new buffer and initialize */ info = malloc(_info.dls_size); info->dls_size = _info.dls_size; info->dls_cnt = _info.dls_cnt; /* obtain sarch path information */ dlinfo(RTLD_SELF, RTLD_DI_SERINFO, (void *)info); path = &info->dls_serpath[0]; for (cnt = 1; cnt <= info->dls_cnt; cnt++, path++) { (void) printf("%2d: %s\n", cnt, path->dls_name); } SEE ALSO rtld(1), dladdr(3), dlopen(3), dlsym(3) HISTORY The dlinfo() function first appeared in the Solaris operating system. In FreeBSD, it first appeared in FreeBSD 4.8. AUTHORS The FreeBSD implementation of the dlinfo() function was originally written by Alexey Zelkin <phantom@FreeBSD.org> and later extended and improved by Alexander Kabaev <kan@FreeBSD.org>. The manual page for this function was written by Alexey Zelkin <phantom@FreeBSD.org>. FreeBSD 12.1 February 14, 2003 DLINFO(3)
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | EXAMPLES | SEE ALSO | HISTORY | AUTHORS
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