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 /* See feature_test_macros(7) */
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, and the order in
20 which they were loaded.
21 The dl_iterate_phdr() function walks through the list of an applica‐
23 tion's shared objects and calls the function callback once for each ob‐
24 ject, until either all shared objects have been processed or callback
25 returns a nonzero value.
26 Each call to callback receives three arguments: info, which is a
28 pointer to a structure containing information about the shared object;
29 size, which is the size of the structure pointed to by info; and data,
30 which is a copy of whatever value was passed by the calling program as
31 the second argument (also named data) in the call to dl_iterate_phdr().
32 The info argument is a structure of the following type:
34 struct dl_phdr_info {
36 ElfW(Addr) dlpi_addr; /* Base address of object */
37 const char *dlpi_name; /* (Null-terminated) name of
38 object */
39 const ElfW(Phdr) *dlpi_phdr; /* Pointer to array of
40 ELF program headers
41 for this object */
42 ElfW(Half) dlpi_phnum; /* # of items in dlpi_phdr */
43 /* The following fields were added in glibc 2.4, after the first
45 version of this structure was available. Check the size
46 argument passed to the dl_iterate_phdr callback to determine
47 whether or not each later member is available. */
48 unsigned long long dlpi_adds;
50 /* Incremented when a new object may
51 have been added */
52 unsigned long long dlpi_subs;
53 /* Incremented when an object may
54 have been removed */
55 size_t dlpi_tls_modid;
56 /* If there is a PT_TLS segment, its module
57 ID as used in TLS relocations, else zero */
58 void *dlpi_tls_data;
59 /* The address of the calling thread's instance
60 of this module's PT_TLS segment, if it has
61 one and it has been allocated in the calling
62 thread, otherwise a null pointer */
63 };
64 (The ElfW() macro definition turns its argument into the name of an ELF
66 data type suitable for the hardware architecture. For example, on a
67 32-bit platform, ElfW(Addr) yields the data type name Elf32_Addr. Fur‐
68 ther information on these types can be found in the <elf.h> and
69 <link.h> header files.)
70 The dlpi_addr field indicates the base address of the shared object
72 (i.e., the difference between the virtual memory address of the shared
73 object and the offset of that object in the file from which it was
74 loaded). The dlpi_name field is a null-terminated string giving the
75 pathname from which the shared object was loaded.
76 To understand the meaning of the dlpi_phdr and dlpi_phnum fields, we
78 need to be aware that an ELF shared object consists of a number of seg‐
79 ments, each of which has a corresponding program header describing the
80 segment. The dlpi_phdr field is a pointer to an array of the program
81 headers for this shared object. The dlpi_phnum field indicates the
82 size of this array.
83 These program headers are structures of the following form:
85 typedef struct {
87 Elf32_Word p_type; /* Segment type */
88 Elf32_Off p_offset; /* Segment file offset */
89 Elf32_Addr p_vaddr; /* Segment virtual address */
90 Elf32_Addr p_paddr; /* Segment physical address */
91 Elf32_Word p_filesz; /* Segment size in file */
92 Elf32_Word p_memsz; /* Segment size in memory */
93 Elf32_Word p_flags; /* Segment flags */
94 Elf32_Word p_align; /* Segment alignment */
95 } Elf32_Phdr;
96 Note that we can calculate the location of a particular program header,
98 x, in virtual memory using the formula:
99 addr == info->dlpi_addr + info->dlpi_phdr[x].p_vaddr;
101 Possible values for p_type include the following (see <elf.h> for fur‐
103 ther details):
104 #define PT_LOAD 1 /* Loadable program segment */
106 #define PT_DYNAMIC 2 /* Dynamic linking information */
107 #define PT_INTERP 3 /* Program interpreter */
108 #define PT_NOTE 4 /* Auxiliary information */
109 #define PT_SHLIB 5 /* Reserved */
110 #define PT_PHDR 6 /* Entry for header table itself */
111 #define PT_TLS 7 /* Thread-local storage segment */
112 #define PT_GNU_EH_FRAME 0x6474e550 /* GCC .eh_frame_hdr segment */
113 #define PT_GNU_STACK 0x6474e551 /* Indicates stack executability */
114 #define PT_GNU_RELRO 0x6474e552 /* Read-only after relocation */
115
117 The dl_iterate_phdr() function returns whatever value was returned by
118 the last call to callback.
119
121 dl_iterate_phdr() has been supported in glibc since version 2.2.4.
122
124 For an explanation of the terms used in this section, see at‐
125 tributes(7).
126 ┌────────────────────────────────────────────┬───────────────┬─────────┐
128 │Interface │ Attribute │ Value │
129 ├────────────────────────────────────────────┼───────────────┼─────────┤
130 │dl_iterate_phdr() │ Thread safety │ MT-Safe │
131 └────────────────────────────────────────────┴───────────────┴─────────┘
132
134 The dl_iterate_phdr() function is not specified in any standard. Vari‐
135 ous other systems provide a version of this function, although details
136 of the returned dl_phdr_info structure differ. On the BSDs and So‐
137 laris, the structure includes the fields dlpi_addr, dlpi_name, dlpi_ph‐
138 dr, and dlpi_phnum in addition to other implementation-specific fields.
139
141 Future versions of the C library may add further fields to the dl_ph‐
142 dr_info structure; in that event, the size argument provides a mecha‐
143 nism for the callback function to discover whether it is running on a
144 system with added fields.
145 The first object visited by callback is the main program. For the main
147 program, the dlpi_name field will be an empty string.
148
150 The following program displays a list of pathnames of the shared ob‐
151 jects it has loaded. For each shared object, the program lists some
152 information (virtual address, size, flags, and type) for each of the
153 objects ELF segments.
154 The following shell session demonstrates the output produced by the
156 program on an x86-64 system. The first shared object for which output
157 is displayed (where the name is an empty string) is the main program.
158 $ ./a.out
160 Name: "" (9 segments)
161 0: [ 0x400040; memsz: 1f8] flags: 0x5; PT_PHDR
162 1: [ 0x400238; memsz: 1c] flags: 0x4; PT_INTERP
163 2: [ 0x400000; memsz: ac4] flags: 0x5; PT_LOAD
164 3: [ 0x600e10; memsz: 240] flags: 0x6; PT_LOAD
165 4: [ 0x600e28; memsz: 1d0] flags: 0x6; PT_DYNAMIC
166 5: [ 0x400254; memsz: 44] flags: 0x4; PT_NOTE
167 6: [ 0x400970; memsz: 3c] flags: 0x4; PT_GNU_EH_FRAME
168 7: [ (nil); memsz: 0] flags: 0x6; PT_GNU_STACK
169 8: [ 0x600e10; memsz: 1f0] flags: 0x4; PT_GNU_RELRO
170 Name: "linux-vdso.so.1" (4 segments)
171 0: [0x7ffc6edd1000; memsz: e89] flags: 0x5; PT_LOAD
172 1: [0x7ffc6edd1360; memsz: 110] flags: 0x4; PT_DYNAMIC
173 2: [0x7ffc6edd17b0; memsz: 3c] flags: 0x4; PT_NOTE
174 3: [0x7ffc6edd17ec; memsz: 3c] flags: 0x4; PT_GNU_EH_FRAME
175 Name: "/lib64/libc.so.6" (10 segments)
176 0: [0x7f55712ce040; memsz: 230] flags: 0x5; PT_PHDR
177 1: [0x7f557145b980; memsz: 1c] flags: 0x4; PT_INTERP
178 2: [0x7f55712ce000; memsz: 1b6a5c] flags: 0x5; PT_LOAD
179 3: [0x7f55716857a0; memsz: 9240] flags: 0x6; PT_LOAD
180 4: [0x7f5571688b80; memsz: 1f0] flags: 0x6; PT_DYNAMIC
181 5: [0x7f55712ce270; memsz: 44] flags: 0x4; PT_NOTE
182 6: [0x7f55716857a0; memsz: 78] flags: 0x4; PT_TLS
183 7: [0x7f557145b99c; memsz: 544c] flags: 0x4; PT_GNU_EH_FRAME
184 8: [0x7f55712ce000; memsz: 0] flags: 0x6; PT_GNU_STACK
185 9: [0x7f55716857a0; memsz: 3860] flags: 0x4; PT_GNU_RELRO
186 Name: "/lib64/ld-linux-x86-64.so.2" (7 segments)
187 0: [0x7f557168f000; memsz: 20828] flags: 0x5; PT_LOAD
188 1: [0x7f55718afba0; memsz: 15a8] flags: 0x6; PT_LOAD
189 2: [0x7f55718afe10; memsz: 190] flags: 0x6; PT_DYNAMIC
190 3: [0x7f557168f1c8; memsz: 24] flags: 0x4; PT_NOTE
191 4: [0x7f55716acec4; memsz: 604] flags: 0x4; PT_GNU_EH_FRAME
192 5: [0x7f557168f000; memsz: 0] flags: 0x6; PT_GNU_STACK
193 6: [0x7f55718afba0; memsz: 460] flags: 0x4; PT_GNU_RELRO
194 Program source
196 #define _GNU_SOURCE
198 #include <link.h>
199 #include <stdlib.h>
200 #include <stdio.h>
201 #include <stdint.h>
202 static int
204 callback(struct dl_phdr_info *info, size_t size, void *data)
205 {
206 char *type;
207 int p_type;
208 printf("Name: \"%s\" (%d segments)\n", info->dlpi_name,
210 info->dlpi_phnum);
211 for (int j = 0; j < info->dlpi_phnum; j++) {
213 p_type = info->dlpi_phdr[j].p_type;
214 type = (p_type == PT_LOAD) ? "PT_LOAD" :
215 (p_type == PT_DYNAMIC) ? "PT_DYNAMIC" :
216 (p_type == PT_INTERP) ? "PT_INTERP" :
217 (p_type == PT_NOTE) ? "PT_NOTE" :
218 (p_type == PT_INTERP) ? "PT_INTERP" :
219 (p_type == PT_PHDR) ? "PT_PHDR" :
220 (p_type == PT_TLS) ? "PT_TLS" :
221 (p_type == PT_GNU_EH_FRAME) ? "PT_GNU_EH_FRAME" :
222 (p_type == PT_GNU_STACK) ? "PT_GNU_STACK" :
223 (p_type == PT_GNU_RELRO) ? "PT_GNU_RELRO" : NULL;
224 printf(" %2d: [%14p; memsz:%7jx] flags: %#jx; ", j,
226 (void *) (info->dlpi_addr + info->dlpi_phdr[j].p_vaddr),
227 (uintmax_t) info->dlpi_phdr[j].p_memsz,
228 (uintmax_t) info->dlpi_phdr[j].p_flags);
229 if (type != NULL)
230 printf("%s\n", type);
231 else
232 printf("[other (%#x)]\n", p_type);
233 }
234 return 0;
236 }
237 int
239 main(int argc, char *argv[])
240 {
241 dl_iterate_phdr(callback, NULL);
242 exit(EXIT_SUCCESS);
244 }
245
247 ldd(1), objdump(1), readelf(1), dladdr(3), dlopen(3), elf(5), ld.so(8)
248 Executable and Linking Format Specification, available at various loca‐
250 tions online.
251
253 This page is part of release 5.12 of the Linux man-pages project. A
254 description of the project, information about reporting bugs, and the
255 latest version of this page, can be found at
256 https://www.kernel.org/doc/man-pages/.
257GNU 2021-03-22 DL_ITERATE_PHDR(3)