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dl_iterate_phdr(3c)
dl_iterate_phdr(3C) Standard C Library Functions dl_iterate_phdr(3C)
NAME
dl_iterate_phdr - walk through a list of objects
SYNOPSIS
#include <link.h>
int dl_iterate_phdr(int (*callback)(struct dl_phdr_info *info,
size_t size, void *data), void *data);
DESCRIPTION
The dl_iterate_phdr() function returns information regarding each ELF
object currently resident in the process address space.
The dl_iterate_phdr() function calls the function callback once for
each object, until either all objects have been processed or callback
returns a non-zero value.
Each call to callback receives three arguments: info, which is a
pointer to a structure containing information about the object; size,
which is the size of the structure pointed to by info; and the data ar‐
gument passed to dl_iterate_phdr() by the caller.
The info argument is a pointer to a structure of the following type:
struct dl_phdr_info {
/* Fields present in all implementations */
ElfW(Addr) dlpi_addr;
const char *dlpi_name;
const ElfW(Phdr) *dlpi_phdr;
ElfW(Half) dlpi_phnum;
/* Additional fields present in this implementation */
u_longlong_t dlpi_adds;
u_longlong_t dlpi_subs;
size_t dlpi_tls_modid;
void *dlpi_tls_data;
};
The ElfW() macro definition turns its argument into the name of an ELF
data type suitable for the hardware architecture, by adding the Elf32_
prefix for 32-bit code, or Elf64_ for 64-bit code.
The first four fields (dlpi_addr, dlpi_name, dlpi_phdr, dlpi_phnum) are
present in all implementations of dl_iterate_phdr(), and can be ac‐
cessed on any system that provides this function. The callback function
must use the size argument to determine if the remaining fields
(dlpi_adds, dlpi_subs, dlpi_tls_modid, dlpi_tls_data) are present. See
EXAMPLES.
The dlpi_addr field is 0 for executable objects (ET_EXEC), and is the
base address at which the object is mapped otherwise. Therefore, the
address of any loadable segment in the program header array can be cal‐
culated as:
addr = info->dlpi_addr + info->dlpi_phdr[x].p_vaddr
dlpi_name gives the pathname of the object.
dlpi_phdr provides a pointer to the program header array for the ob‐
ject, and dlpi_phnum specifies the number of program headers found in
the array.
dlpi_adds provides the number of objects that have been mapped into the
current process since it started, and dlpi_subs provides the number of
objects that have been unmapped. See NOTES.
dlpi_tls_modid provides the module ID of the object PT_TLS segment if
one is present, and 0 otherwise.
dlpi_tls_data provides the address of the calling thread's instance of
this module's PT_TLS segment, if it has one, and it has been allocated
in the calling thread, and is 0 otherwise.
See the Oracle Solaris 11.4 Linkers and Libraries Guide for more infor‐
mation about ELF objects, and the information contained in program
headers.
EXAMPLES
Example 1 Display all currently mapped objects
The following program displays the pathnames of currently mapped ob‐
jects. For each object, the virtual address of each loadable segment is
shown.
#include <link.h>
#include <stdlib.h>
#include <stdio.h>
static int
callback(struct dl_phdr_info *info, size_t size,
void *data)
{
int j;
(void) printf("name=%s (%d program headers)\n",
info->dlpi_name, info->dlpi_phnum);
for (j = 0; j < info->dlpi_phnum; j++) {
if (info->dlpi_phdr[j].p_type == PT_LOAD) {
(void) printf("\t[%d] 0x%p\n", j,
(void *) (info->dlpi_addr +
info->dlpi_phdr[j].p_vaddr));
}
}
return 0;
}
int
main(int argc, char *argv[])
{
dl_iterate_phdr(callback, NULL);
return(0);
}
Example 2 Testing for optional dl_phdr_info fields
Every implementation of dl_iterate_phdr is required to supply the first
four fields in struct dl_phdr_info described above. The callback is al‐
lowed to assume that they are present and to access them without first
testing for their presence. Additional fields may be present. The call‐
back must use the size argument to test for their presence before ac‐
cessing them. This example demonstrates how a callback function can de‐
tect the presence of the dlpi_adds and dlpi_subs fields described
above:
static int
callback(struct dl_phdr_info *info, size_t size,
void *data)
{
/*
* This must match the definition of dl_phdr_info,
* as defined in <link.h>. It is used to determine
* whether the info structure contains optional
* fields.
*/
struct dl_phdr_info_test {
ElfW(Addr) dlpi_addr;
const char *dlpi_name;
const ElfW(Phdr) *dlpi_phdr;
ElfW(Half) dlpi_phnum;
u_longlong_t dlpi_adds;
u_longlong_t dlpi_subs;
size_t dlpi_tls_modid;
void *dlpi_tls_data;
};
(void) printf("object: %s\n", info->dlpi_name);
(void) printf(" addr: 0x%p\n",
(u_longlong_t)info->dlpi_addr);
(void) printf(" phdr: 0x%p\n",
(u_longlong_t)info->dlpi_phdr);
(void) printf(" phnum: %d\n",
(int)info->dlpi_phnum);
if (size >= offsetof(struct dl_phdr_info_test, dlpi_adds))
(void) printf(" adds: %llu\n",
info->dlpi_adds);
if (size >= offsetof(struct dl_phdr_info_test, dlpi_subs))
(void) printf(" subs: %llu\n",
info->dlpi_subs);
if (size >= offsetof(struct dl_phdr_info_test, dlpi_tls_modid))
(void) printf(" tls_modid: %zu\n",
info->dlpi_tls_modid);
if (size >= offsetof(struct dl_phdr_info_test, dlpi_tls_data))
(void) printf(" tls_data: %p\n",
info->dlpi_tls_data);
return (0);
}
RETURN VALUES
The dl_iterate_phdr() function returns whatever value was returned by
the last call to callback.
USAGE
The dl_iterate_phdr() function is a member of a family of functions
that give the user direct access to the dynamic linking facilities.
This family of functions is available only to dynamically-linked
processes. See the Oracle Solaris 11.4 Linkers and Libraries Guide.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted _ MT-LevelMT-Safe
SEE ALSO
ld(1), ld.so.1(1), dladdr(3C), dlclose(3C), dldump(3C), dlerror(3C),
dlinfo(3C), dlopen(3C), dlsym(3C), attributes(7), standards(7)
Oracle Solaris 11.4 Linkers and Libraries Guide
NOTES
dl_iterate_phdr() was originally defined by the Linux operating system,
and is contained in the Linux Standard Base (LSB).
The behavior of dl_iterate_phdr() when a callback function causes a new
object to be loaded, either via lazy loading or a call to dlopen(), is
undefined. The call to dl_iterate_phdr() that triggers the load may or
may not issue a callback for the new object. This depends on the cur‐
rent position of dl_iterate_phdr() in the list of known objects when
the new object is added. The caller must make no assumptions about this
case.
dl_iterate_phdr() callbacks must not unload objects. If a call to dl‐
close() is detected from within the callback function, dl_iter‐
ate_phdr() immediately terminates the iteration operation and returns a
value of -1.
If two separate calls to dl_iterate_phdr() provide the same two values
for dlpi_adds and dlpi_subs, the caller may safely assume that the
process object state has not changed between the two calls. An applica‐
tion can use this information to cache object data, and avoid unneces‐
sary iteration. In such a scenario, the first call to the callback
function would check to see if a cache exists, and that dlpi_adds and
dlpi_subs have not changed since the last call to dl_iterate_phdr(),
and if so, return a non-zero value to terminate the iteration operation
immediately.
HISTORY
The dlpi_tls_modid and dlpi_tls_data fields were added to the
dl_phdr_info structure in Oracle Solaris 11.4.10.
The dl_iterate_phdr() function and the dl_phdr_info structure were
added in Solaris 10 8/11 (Update 10).
Oracle Solaris 11.4 27 Aug 2025 dl_iterate_phdr(3C)