1DL_ITERATE_PHDR(3) Linux Programmer's Manual DL_ITERATE_PHDR(3)
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6 dl_iterate_phdr - walk through list of shared objects
7
9 #define _GNU_SOURCE
10 #include <link.h>
11 int dl_iterate_phdr(
13 int (*callback) (struct dl_phdr_info *info,
14 size_t size, void *data),
15 void *data);
16
18 The dl_iterate_phdr() function allows an application to inquire at run
19 time to find out which shared objects it has loaded.
20 The dl_iterate_phdr() function walks through the list of an applica‐
22 tion's shared objects and calls the function callback once for each
23 object, until either all shared objects have been processed or callback
24 returns a non-zero value.
25 Each call to callback receives three arguments: info, which is a
27 pointer to a structure containing information about the shared object;
28 size, which is the size of the structure pointed to by info; and data,
29 which is a copy of whatever value was passed by the calling program as
30 the second argument (also named data) in the call to dl_iterate_phdr().
31 The info argument is a structure of the following type:
33 struct dl_phdr_info {
35 ElfW(Addr) dlpi_addr; /* Base address of object */
36 const char *dlpi_name; /* (Null-terminated) name of
37 object */
38 const ElfW(Phdr) *dlpi_phdr; /* Pointer to array of
39 ELF program headers
40 for this object */
41 ElfW(Half) dlpi_phnum; /* # of items in dlpi_phdr */
42 };
43 (The ElfW() macro definition turns its argument into the name of an ELF
45 data type suitable for the hardware architecture. For example, on a
46 32-bit platform, ElfW(Addr) yields the data type name Elf32_Addr. Fur‐
47 ther information on these types can be found in the <elf.h> and
48 <link.h> header files.)
49 The dlpi_addr field indicates the base address of the shared object
51 (i.e., the difference between the virtual memory address of the shared
52 object and the offset of that object in the file from which it was
53 loaded). The dlpi_name field is a null-terminated string giving the
54 pathname from which the shared object was loaded.
55 To understand the meaning of the dlpi_phdr and dlpi_phnum fields, we
57 need to be aware that an ELF shared object consists of a number of seg‐
58 ments, each of which has a corresponding program header describing the
59 segment. The dlpi_phdr field is a pointer to an array of the program
60 headers for this shared object. The dlpi_phnum field indicates the
61 size of this array.
62 These program headers are structures of the following form:
64 typedef struct {
66 Elf32_Word p_type; /* Segment type */
67 Elf32_Off p_offset; /* Segment file offset */
68 Elf32_Addr p_vaddr; /* Segment virtual address */
69 Elf32_Addr p_paddr; /* Segment physical address */
70 Elf32_Word p_filesz; /* Segment size in file */
71 Elf32_Word p_memsz; /* Segment size in memory */
72 Elf32_Word p_flags; /* Segment flags */
73 Elf32_Word p_align; /* Segment alignment */
74 } Elf32_Phdr;
75 Note that we can calculate the location of a particular program header,
77 x, in virtual memory using the formula:
78 addr == info->dlpi_addr + info->dlpi_phdr[x].p_vaddr;
80
82 The dl_iterate_phdr() function returns whatever value was returned by
83 the last call to callback.
84
86 dl_iterate_phdr() has been supported in glibc since version 2.2.4.
87
89 The dl_iterate_phdr() function is Linux-specific and should be avoided
90 in portable applications.
91
93 The following program displays a list of pathnames of the shared
94 objects it has loaded. For each shared object, the program lists the
95 virtual addresses at which the object's ELF segments are loaded.
96 #define _GNU_SOURCE
98 #include <link.h>
99 #include <stdlib.h>
100 #include <stdio.h>
101 static int
103 callback(struct dl_phdr_info *info, size_t size, void *data)
104 {
105 int j;
106 printf("name=%s (%d segments)\n", info->dlpi_name,
108 info->dlpi_phnum);
109 for (j = 0; j < info->dlpi_phnum; j++)
111 printf("\t\t header %2d: address=%10p\n", j,
112 (void *) (info->dlpi_addr + info->dlpi_phdr[j].p_vaddr));
113 return 0;
114 }
115 int
117 main(int argc, char *argv[])
118 {
119 dl_iterate_phdr(callback, NULL);
120 exit(EXIT_SUCCESS);
122 }
123
125 ldd(1), objdump(1), readelf(1), dlopen(3), elf(5), fea‐
126 ture_test_macros(7), ld.so(8), and the Executable and Linking Format
127 Specification available at various locations online.
128
130 This page is part of release 3.22 of the Linux man-pages project. A
131 description of the project, and information about reporting bugs, can
132 be found at http://www.kernel.org/doc/man-pages/.
133GNU 2007-05-18 DL_ITERATE_PHDR(3)