@node Dynamic Linker @c @node Dynamic Linker, Internal Probes, Threads, Top @c %MENU% Loading programs and shared objects. @chapter Dynamic Linker @cindex dynamic linker @cindex dynamic loader The @dfn{dynamic linker} is responsible for loading dynamically linked programs and their dependencies (in the form of shared objects). The dynamic linker in @theglibc{} also supports loading shared objects (such as plugins) later at run time. Dynamic linkers are sometimes called @dfn{dynamic loaders}. @menu * Dynamic Linker Introspection:: Interfaces for querying mapping information. @end menu @node Dynamic Linker Introspection @section Dynamic Linker Introspection @Theglibc{} provides various functions for querying information from the dynamic linker. @deftypefun {int} dlinfo (void *@var{handle}, int @var{request}, void *@var{arg}) @safety{@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}} @standards{GNU, dlfcn.h} This function returns information about @var{handle} in the memory location @var{arg}, based on @var{request}. The @var{handle} argument must be a pointer returned by @code{dlopen} or @code{dlmopen}; it must not have been closed by @code{dlclose}. On success, @code{dlinfo} returns 0. If there is an error, the function returns @math{-1}, and @code{dlerror} can be used to obtain a corresponding error message. The following operations are defined for use with @var{request}: @vtable @code @item RTLD_DI_LINKMAP The corresponding @code{struct link_map} pointer for @var{handle} is written to @code{*@var{arg}}. The @var{arg} argument must be the address of an object of type @code{struct link_map *}. @item RTLD_DI_LMID The namespace identifier of @var{handle} is written to @code{*@var{arg}}. The @var{arg} argument must be the address of an object of type @code{Lmid_t}. @item RTLD_DI_ORIGIN The value of the @code{$ORIGIN} dynamic string token for @var{handle} is written to the character array starting at @var{arg} as a null-terminated string. This request type should not be used because it is prone to buffer overflows. @item RTLD_DI_SERINFO @itemx RTLD_DI_SERINFOSIZE These requests can be used to obtain search path information for @var{handle}. For both requests, @var{arg} must point to a @code{Dl_serinfo} object. The @code{RTLD_DI_SERINFOSIZE} request must be made first; it updates the @code{dls_size} and @code{dls_cnt} members of the @code{Dl_serinfo} object. The caller should then allocate memory to store at least @code{dls_size} bytes and pass that buffer to a @code{RTLD_DI_SERINFO} request. This second request fills the @code{dls_serpath} array. The number of array elements was returned in the @code{dls_cnt} member in the initial @code{RTLD_DI_SERINFOSIZE} request. The caller is responsible for freeing the allocated buffer. This interface is prone to buffer overflows in multi-threaded processes because the required size can change between the @code{RTLD_DI_SERINFOSIZE} and @code{RTLD_DI_SERINFO} requests. @item RTLD_DI_TLS_DATA This request writes the address of the TLS block (in the current thread) for the shared object identified by @var{handle} to @code{*@var{arg}}. The argument @var{arg} must be the address of an object of type @code{void *}. A null pointer is written if the object does not have any associated TLS block. @item RTLD_DI_TLS_MODID This request writes the TLS module ID for the shared object @var{handle} to @code{*@var{arg}}. The argument @var{arg} must be the address of an object of type @code{size_t}. The module ID is zero if the object does not have an associated TLS block. @end vtable The @code{dlinfo} function is a GNU extension. @end deftypefun @c FIXME these are undocumented: @c dladdr @c dladdr1 @c dlclose @c dlerror @c dlmopen @c dlopen @c dlsym @c dlvsym