Linker and Libraries Guide

Scanning Loadable Objects

You can obtain information for each object maintained on the runtime linkers link-map is achieved by using the following structure, defined in rtld_db.h.

typedef struct rd_loadobj {
        psaddr_t        rl_nameaddr;
        unsigned        rl_flags;
        psaddr_t        rl_base;
        psaddr_t        rl_data_base;
        unsigned        rl_lmident;
        psaddr_t        rl_refnameaddr;
        psaddr_t        rl_plt_base;
        unsigned        rl_plt_size;
        psaddr_t        rl_bend;
        psaddr_t        rl_padstart;
        psaddr_t        rl_padend;
        psaddt_t        rl_dynamic;
} rd_loadobj_t;

Notice that all addresses given in this structure, including string pointers, are addresses in the target process and not in the address space of the controlling process itself.


A pointer to a string that contains the name of the dynamic object.


With revision RD_VERSION2, dynamically loaded relocatable objects are identified with RD_FLG_MEM_OBJECT.


The base address of the dynamic object.


The base address of the data segment of the dynamic object.


The link-map identifier (see Establishing a Namespace).


If the dynamic object is a standard filter, then this points to the name of the filtees.

rl_plt_base, rl_plt_size

These elements are present for backward compatibility and are currently unused.


The end address of the object (text + data + bss). With revision RD_VERSION2, a dynamically loaded relocatable object will cause this element to point to the end of the created object, which will include its section headers.


The base address of the padding before the dynamic object (refer to Dynamic Object Padding).


The base address of the padding after the dynamic object (refer to Dynamic Object Padding).


This field, added with RD_VERSION2, provides the base address of the object's dynamic section, which allows reference to such entries as DT_CHECKSUM (see Table 7–32).

The rd_loadobj_iter() routine uses this object data structure to access information from the runtime linker's link-map lists.


This function iterates over all dynamic objects currently loaded in the target process.

typedef int rl_iter_f(const rd_loadobj_t *, void *);
rd_err_e rd_loadobj_iter(rd_agent_t * rap, rl_iter_f * cb,
        void * clnt_data);

On each iteration the imported function specified by cb is called. clnt_data can be used to pass data to the cb call. Information about each object is returned by means of a pointer to a volatile (stack allocated) rd_loadobj_t structure.

Return codes from the cb routine are examined by rd_loadobj_iter() and have the following meaning.

  • 1 – continue processing link-maps.

  • 0 – stop processing link-maps and return control to the controlling process.

rd_loadobj_iter() returns RD_OK on success. A return of RD_NOMAPS indicates the runtime linker has not yet loaded the initial link-maps.