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dl_iterate_phdr(3) [freebsd man page]

DL_ITERATE_PHDR(3)					   BSD Library Functions Manual 					DL_ITERATE_PHDR(3)

NAME
dl_iterate_phdr -- iterate over program headers LIBRARY
For the dynamically linked binaries, the service is provided by ld-elf.so.1(1) dynamic linker. Statically linked programs use an implementa- tion of dl_iterate_phdr() from libc. SYNOPSIS
#include <link.h> int dl_iterate_phdr(int (*callback)(struct dl_phdr_info *, size_t, void *), void *data); DESCRIPTION
The dl_iterate_phdr() function iterates over all ELF objects loaded into a process's address space, calling callback for each object, passing it information about the object's program headers and the data argument. The iteration is aborted when all objects are passed, or when the next callback call returns non-zero value. The information about the program headers is passed in a structure that is defined as: struct dl_phdr_info { Elf_Addr dlpi_addr; const char *dlpi_name; const Elf_Phdr *dlpi_phdr; Elf_Half dlpi_phnum; unsigned long long int dlpi_adds; unsigned long long int dlpi_subs; size_t dlpi_tls_modid; void *dlpi_tls_data; }; The members of struct dl_phdr_info have the following meaning: dlpi_addr The base address at which the object is mapped into the address space of the calling process. dlpi_name The pathname of the ELF object. dlpi_phdr A pointer to the object's program headers. dlpi_phnum The number of program headers in the object. dlpi_adds The counter of the object loads performed by the dynamic linker. dlpi_subs The counter of the object unloads performed by the dynamic linker. dlpi_tls_modid The TLS index of the object. dlpi_tls_data A pointer to the initialization data for the object TLS segment. Future versions of FreeBSD might add more members to this structure. To make it possible for programs to check whether any new members have been added, the size of the structure is passed as an second argument to callback. The third argument to callback is the data value passed to the call to dl_iterate_phdr(), allowing the callback to have a context. RETURN VALUES
The dl_iterate_phdr() returns the value returned by the last callback call executed. SEE ALSO
ld(1), ld-elf.so.1(1), dlopen(3), elf(5) HISTORY
The dl_iterate_phdr function first appeared in FreeBSD 7.0. BSD
October 9, 2014 BSD

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DL_ITERATE_PHDR(3)					     Linux Programmer's Manual						DL_ITERATE_PHDR(3)

NAME
dl_iterate_phdr - walk through list of shared objects SYNOPSIS
#define _GNU_SOURCE #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 allows an application to inquire at run time to find out which shared objects it has loaded. The dl_iterate_phdr() function walks through the list of an application's shared objects and calls the function callback once for each object, until either all shared objects have been processed or callback returns a nonzero value. Each call to callback receives three arguments: info, which is a pointer to a structure containing information about the shared object; size, which is the size of the structure pointed to by info; and data, which is a copy of whatever value was passed by the calling program as the second argument (also named data) in the call to dl_iterate_phdr(). The info argument is a structure of the following type: struct dl_phdr_info { ElfW(Addr) dlpi_addr; /* Base address of object */ const char *dlpi_name; /* (Null-terminated) name of object */ const ElfW(Phdr) *dlpi_phdr; /* Pointer to array of ELF program headers for this object */ ElfW(Half) dlpi_phnum; /* # of items in dlpi_phdr */ }; (The ElfW() macro definition turns its argument into the name of an ELF data type suitable for the hardware architecture. For example, on a 32-bit platform, ElfW(Addr) yields the data type name Elf32_Addr. Further information on these types can be found in the <elf.h> and <link.h> header files.) The dlpi_addr field indicates the base address of the shared object (i.e., the difference between the virtual memory address of the shared object and the offset of that object in the file from which it was loaded). The dlpi_name field is a null-terminated string giving the pathname from which the shared object was loaded. To understand the meaning of the dlpi_phdr and dlpi_phnum fields, we need to be aware that an ELF shared object consists of a number of segments, each of which has a corresponding program header describing the segment. The dlpi_phdr field is a pointer to an array of the program headers for this shared object. The dlpi_phnum field indicates the size of this array. These program headers are structures of the following form: typedef struct { Elf32_Word p_type; /* Segment type */ Elf32_Off p_offset; /* Segment file offset */ Elf32_Addr p_vaddr; /* Segment virtual address */ Elf32_Addr p_paddr; /* Segment physical address */ Elf32_Word p_filesz; /* Segment size in file */ Elf32_Word p_memsz; /* Segment size in memory */ Elf32_Word p_flags; /* Segment flags */ Elf32_Word p_align; /* Segment alignment */ } Elf32_Phdr; Note that we can calculate the location of a particular program header, x, in virtual memory using the formula: addr == info->dlpi_addr + info->dlpi_phdr[x].p_vaddr; RETURN VALUE
The dl_iterate_phdr() function returns whatever value was returned by the last call to callback. VERSIONS
dl_iterate_phdr() has been supported in glibc since version 2.2.4. CONFORMING TO
The dl_iterate_phdr() function is Linux-specific and should be avoided in portable applications. EXAMPLE
The following program displays a list of pathnames of the shared objects it has loaded. For each shared object, the program lists the vir- tual addresses at which the object's ELF segments are loaded. #define _GNU_SOURCE #include <link.h> #include <stdlib.h> #include <stdio.h> static int callback(struct dl_phdr_info *info, size_t size, void *data) { int j; printf("name=%s (%d segments) ", info->dlpi_name, info->dlpi_phnum); for (j = 0; j < info->dlpi_phnum; j++) printf(" header %2d: address=%10p ", j, (void *) (info->dlpi_addr + info->dlpi_phdr[j].p_vaddr)); return 0; } int main(int argc, char *argv[]) { dl_iterate_phdr(callback, NULL); exit(EXIT_SUCCESS); } SEE ALSO
ldd(1), objdump(1), readelf(1), dlopen(3), elf(5), feature_test_macros(7), ld.so(8), and the Executable and Linking Format Specification available at various locations online. COLOPHON
This page is part of release 3.27 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. GNU
2007-05-18 DL_ITERATE_PHDR(3)

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