Scanning Loadable Objects

Information for each object maintained on the runtime linkers link-map can be obtained from 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;
        unsigned long   rl_tlsmodid;
} rd_loadobj_t;

All addresses provided in this structure, including string pointers, are addresses in the target process and not in the address space of the controlling process itself.

rl_nameaddr

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

rl_flags

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

rl_base

The base address of the dynamic object.

rl_data_base

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

rl_lmident

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

rl_refnameaddr

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.

rl_bend

The end address of the object (text + data + bss). With revision RD_VERSION2, the end address of a dynamically loaded relocatable object is the end of the created object, including the object section headers.

rl_padstart

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

rl_padend

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

rl_dynamic

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 ELF Dynamic Array Tags).

rl_tlsmodid

This field, added with RD_VERSION4, provides the module identifier for thread local storage, TLS, references. The module identifier is a small integer unique to the object. This identifier can be passed to the libc_db function td_thr_tlsbase() in order to obtain the base address of a thread's TLS block for the object in question. See td_thr_tlsbase(3C_DB).

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

rd_loadobj_iter()

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.