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21 .TH DL_ITERATE_PHDR 3 "Linux 2.4.21" "Linux Programmer's Manual"
23 dl_iterate_phdr \- walk through list of shared objects
29 \fBint dl_iterate_phdr(\fP
30 \fBint (*\fPcallback\fB) \
31 (struct dl_phdr_info *\fPinfo\fB,\fP
32 \fBsize_t\fP size\fB, void *\fPdata\fB),\fP
33 \fBvoid *\fPdata\fB);\fP
37 .BR dl_iterate_phdr ()
38 function allows an application to inquire at run-time to find
39 out which shared objects it has loaded.
42 .BR dl_iterate_phdr ()
43 function walks through the list of an
44 application's shared objects and calls the function
47 until either all shared objects have been processed or
49 returns a non-zero value.
53 receives three arguments:
55 which is a pointer to a structure containing information
56 about the shared object;
58 which is the size of the structure pointed to by
62 which is a copy of whatever value was passed by the calling
63 program as the second argument (also named
66 .BR dl_iterate_phdr ().
70 argument is a structure of the following type:
74 ElfW(Addr) dlpi_addr; /* Base address of object */
75 const char *dlpi_name; /* (Null-terminated) name of
77 const ElfW(Phdr) *dlpi_phdr; /* Pointer to array of
80 ElfW(Half) dlpi_phnum; /* # of items in 'dlpi_phdr' */
86 macro definition turns its argument into the name of an ELF data
87 type suitable for the hardware architecture.
88 For example, on a 32-bit platform,
89 ElfW(Addr) yields the data type name Elf32_Addr.
90 Further information on these types can be found in the
91 .IR <elf.h> " and " <link.h>
96 field indicates the base address of the shared object
97 (i.e., the difference between the virtual memory address of
98 the shared object and the offset of that object in the file
99 from which it was loaded).
102 field is a null-terminated string giving the pathname
103 from which the shared object was loaded.
105 To understand the meaning of the
109 fields, we need to be aware that an ELF shared object consists
110 of a number of segments, each of which has a corresponding
111 program header describing the segment.
114 field is a pointer to an array of the program headers for this
118 field indicates the size of this array.
120 These program headers are structures of the following form:
125 Elf32_Word p_type; /* Segment type */
126 Elf32_Off p_offset; /* Segment file offset */
127 Elf32_Addr p_vaddr; /* Segment virtual address */
128 Elf32_Addr p_paddr; /* Segment physical address */
129 Elf32_Word p_filesz; /* Segment size in file */
130 Elf32_Word p_memsz; /* Segment size in memory */
131 Elf32_Word p_flags; /* Segment flags */
132 Elf32_Word p_align; /* Segment alignment */
136 Note that we can calculate the location of a particular program header,
138 in virtual memory using the formula:
141 addr == info->dlpi_addr + info->dlpi_phdr[x].p_vaddr;
144 The following program displays a list of pathnames of the
145 shared objects it has loaded.
146 For each shared object, the program lists the virtual addresses
147 at which the object's ELF segments are loaded.
156 callback(struct dl_phdr_info *info, size_t size, void *data)
160 printf("name=%s (%d segments)\\n", info->dlpi_name,
163 for (j = 0; j < info->dlpi_phnum; j++)
164 printf("\\t\\t header %2d: address=%10p\\n", j,
165 (void *) (info->dlpi_addr + info->dlpi_phdr[j].p_vaddr));
170 main(int argc, char *argv[])
172 dl_iterate_phdr(callback, NULL);
179 .BR dl_iterate_phdr ()
180 function returns whatever value was returned by the last call to
184 .BR dl_iterate_phdr ()
185 function is Linux specific and should be avoided in portable applications.
193 .I "Executable and Linking Format Specification"
194 available at various locations online.