mirror of https://github.com/mkerrisk/man-pages
365 lines
12 KiB
Groff
365 lines
12 KiB
Groff
.\" Copyright (c) 2003, 2017 by Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.TH DL_ITERATE_PHDR 3 2020-11-01 "GNU" "Linux Programmer's Manual"
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.SH NAME
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dl_iterate_phdr \- walk through list of shared objects
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.SH SYNOPSIS
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.nf
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.BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */"
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.B #include <link.h>
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.PP
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.BI "int dl_iterate_phdr("
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.BI " int (*" callback ")(struct dl_phdr_info *" info ,
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.BI " size_t " size ", void *" data "),"
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.BI " void *" data ");"
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.fi
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.SH DESCRIPTION
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The
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.BR dl_iterate_phdr ()
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function allows an application to inquire at run time to find
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out which shared objects it has loaded,
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and the order in which they were loaded.
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.PP
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The
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.BR dl_iterate_phdr ()
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function walks through the list of an
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application's shared objects and calls the function
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.I callback
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once for each object,
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until either all shared objects have been processed or
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.I callback
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returns a nonzero value.
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.PP
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Each call to
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.I callback
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receives three arguments:
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.IR info ,
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which is a pointer to a structure containing information
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about the shared object;
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.IR size ,
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which is the size of the structure pointed to by
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.IR info ;
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and
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.IR data ,
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which is a copy of whatever value was passed by the calling
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program as the second argument (also named
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.IR data )
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in the call to
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.BR dl_iterate_phdr ().
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.PP
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The
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.I info
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argument is a structure of the following type:
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.PP
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.in +4n
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.EX
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struct dl_phdr_info {
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ElfW(Addr) dlpi_addr; /* Base address of object */
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const char *dlpi_name; /* (Null-terminated) name of
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object */
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const ElfW(Phdr) *dlpi_phdr; /* Pointer to array of
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ELF program headers
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for this object */
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ElfW(Half) dlpi_phnum; /* # of items in \fIdlpi_phdr\fP */
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/* The following fields were added in glibc 2.4, after the first
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version of this structure was available. Check the \fIsize\fP
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argument passed to the dl_iterate_phdr callback to determine
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whether or not each later member is available. */
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unsigned long long dlpi_adds;
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/* Incremented when a new object may
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have been added */
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unsigned long long dlpi_subs;
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/* Incremented when an object may
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have been removed */
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size_t dlpi_tls_modid;
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/* If there is a PT_TLS segment, its module
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ID as used in TLS relocations, else zero */
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void *dlpi_tls_data;
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/* The address of the calling thread\(aqs instance
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of this module\(aqs PT_TLS segment, if it has
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one and it has been allocated in the calling
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thread, otherwise a null pointer */
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};
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.EE
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.in
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.PP
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(The
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.IR ElfW ()
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macro definition turns its argument into the name of an ELF data
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type suitable for the hardware architecture.
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For example, on a 32-bit platform,
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.I ElfW(Addr)
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yields the data type name
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.IR Elf32_Addr .
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Further information on these types can be found in the
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.IR <elf.h> " and " <link.h>
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header files.)
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.PP
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The
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.I dlpi_addr
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field indicates the base address of the shared object
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(i.e., the difference between the virtual memory address of
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the shared object and the offset of that object in the file
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from which it was loaded).
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The
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.I dlpi_name
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field is a null-terminated string giving the pathname
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from which the shared object was loaded.
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.PP
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To understand the meaning of the
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.I dlpi_phdr
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and
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.I dlpi_phnum
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fields, we need to be aware that an ELF shared object consists
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of a number of segments, each of which has a corresponding
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program header describing the segment.
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The
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.I dlpi_phdr
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field is a pointer to an array of the program headers for this
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shared object.
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The
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.I dlpi_phnum
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field indicates the size of this array.
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.PP
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These program headers are structures of the following form:
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.PP
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.in +4n
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.EX
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typedef struct {
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Elf32_Word p_type; /* Segment type */
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Elf32_Off p_offset; /* Segment file offset */
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Elf32_Addr p_vaddr; /* Segment virtual address */
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Elf32_Addr p_paddr; /* Segment physical address */
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Elf32_Word p_filesz; /* Segment size in file */
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Elf32_Word p_memsz; /* Segment size in memory */
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Elf32_Word p_flags; /* Segment flags */
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Elf32_Word p_align; /* Segment alignment */
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} Elf32_Phdr;
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.EE
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.in
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.PP
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Note that we can calculate the location of a particular program header,
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.IR x ,
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in virtual memory using the formula:
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.PP
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.in +4n
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.EX
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addr == info\->dlpi_addr + info\->dlpi_phdr[x].p_vaddr;
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.EE
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.in
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.PP
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Possible values for
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.I p_type
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include the following (see
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.IR <elf.h>
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for further details):
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.PP
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.in +4n
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.EX
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#define PT_LOAD 1 /* Loadable program segment */
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#define PT_DYNAMIC 2 /* Dynamic linking information */
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#define PT_INTERP 3 /* Program interpreter */
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#define PT_NOTE 4 /* Auxiliary information */
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#define PT_SHLIB 5 /* Reserved */
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#define PT_PHDR 6 /* Entry for header table itself */
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#define PT_TLS 7 /* Thread-local storage segment */
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#define PT_GNU_EH_FRAME 0x6474e550 /* GCC .eh_frame_hdr segment */
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#define PT_GNU_STACK 0x6474e551 /* Indicates stack executability */
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.\" For PT_GNU_STACK, see http://www.airs.com/blog/archives/518
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#define PT_GNU_RELRO 0x6474e552 /* Read-only after relocation */
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.EE
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.in
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.SH RETURN VALUE
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The
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.BR dl_iterate_phdr ()
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function returns whatever value was returned by the last call to
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.IR callback .
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.SH VERSIONS
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.BR dl_iterate_phdr ()
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has been supported in glibc since version 2.2.4.
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.SH ATTRIBUTES
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For an explanation of the terms used in this section, see
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.BR attributes (7).
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.ad l
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.nh
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.TS
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allbox;
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lbx lb lb
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l l l.
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Interface Attribute Value
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T{
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.BR dl_iterate_phdr ()
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T} Thread safety MT-Safe
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.TE
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.hy
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.ad
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.sp 1
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.SH CONFORMING TO
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The
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.BR dl_iterate_phdr ()
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function is not specified in any standard.
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Various other systems provide a version of this function,
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although details of the returned
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.I dl_phdr_info
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structure differ.
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On the BSDs and Solaris, the structure includes the fields
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.IR dlpi_addr ,
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.IR dlpi_name ,
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.IR dlpi_phdr ,
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and
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.IR dlpi_phnum
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in addition to other implementation-specific fields.
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.SH NOTES
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Future versions of the C library may add further fields to the
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.IR dl_phdr_info
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structure; in that event, the
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.I size
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argument provides a mechanism for the callback function to discover
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whether it is running on a system with added fields.
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.PP
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The first object visited by
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.IR callback
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is the main program.
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For the main program, the
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.I dlpi_name
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field will be an empty string.
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.SH EXAMPLES
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The following program displays a list of pathnames of the
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shared objects it has loaded.
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For each shared object, the program lists some information
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(virtual address, size, flags, and type)
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for each of the objects ELF segments.
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.PP
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The following shell session demonstrates the output
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produced by the program on an x86-64 system.
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The first shared object for which output is displayed
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(where the name is an empty string)
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is the main program.
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.PP
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.in +4n
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.EX
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$ \fB./a.out\fP
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Name: "" (9 segments)
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0: [ 0x400040; memsz: 1f8] flags: 0x5; PT_PHDR
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1: [ 0x400238; memsz: 1c] flags: 0x4; PT_INTERP
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2: [ 0x400000; memsz: ac4] flags: 0x5; PT_LOAD
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3: [ 0x600e10; memsz: 240] flags: 0x6; PT_LOAD
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4: [ 0x600e28; memsz: 1d0] flags: 0x6; PT_DYNAMIC
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5: [ 0x400254; memsz: 44] flags: 0x4; PT_NOTE
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6: [ 0x400970; memsz: 3c] flags: 0x4; PT_GNU_EH_FRAME
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7: [ (nil); memsz: 0] flags: 0x6; PT_GNU_STACK
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8: [ 0x600e10; memsz: 1f0] flags: 0x4; PT_GNU_RELRO
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Name: "linux-vdso.so.1" (4 segments)
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0: [0x7ffc6edd1000; memsz: e89] flags: 0x5; PT_LOAD
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1: [0x7ffc6edd1360; memsz: 110] flags: 0x4; PT_DYNAMIC
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2: [0x7ffc6edd17b0; memsz: 3c] flags: 0x4; PT_NOTE
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3: [0x7ffc6edd17ec; memsz: 3c] flags: 0x4; PT_GNU_EH_FRAME
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Name: "/lib64/libc.so.6" (10 segments)
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0: [0x7f55712ce040; memsz: 230] flags: 0x5; PT_PHDR
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1: [0x7f557145b980; memsz: 1c] flags: 0x4; PT_INTERP
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2: [0x7f55712ce000; memsz: 1b6a5c] flags: 0x5; PT_LOAD
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3: [0x7f55716857a0; memsz: 9240] flags: 0x6; PT_LOAD
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4: [0x7f5571688b80; memsz: 1f0] flags: 0x6; PT_DYNAMIC
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5: [0x7f55712ce270; memsz: 44] flags: 0x4; PT_NOTE
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6: [0x7f55716857a0; memsz: 78] flags: 0x4; PT_TLS
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7: [0x7f557145b99c; memsz: 544c] flags: 0x4; PT_GNU_EH_FRAME
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8: [0x7f55712ce000; memsz: 0] flags: 0x6; PT_GNU_STACK
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9: [0x7f55716857a0; memsz: 3860] flags: 0x4; PT_GNU_RELRO
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Name: "/lib64/ld-linux-x86-64.so.2" (7 segments)
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0: [0x7f557168f000; memsz: 20828] flags: 0x5; PT_LOAD
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1: [0x7f55718afba0; memsz: 15a8] flags: 0x6; PT_LOAD
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2: [0x7f55718afe10; memsz: 190] flags: 0x6; PT_DYNAMIC
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3: [0x7f557168f1c8; memsz: 24] flags: 0x4; PT_NOTE
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4: [0x7f55716acec4; memsz: 604] flags: 0x4; PT_GNU_EH_FRAME
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5: [0x7f557168f000; memsz: 0] flags: 0x6; PT_GNU_STACK
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6: [0x7f55718afba0; memsz: 460] flags: 0x4; PT_GNU_RELRO
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.EE
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.in
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.SS Program source
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\&
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.EX
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#define _GNU_SOURCE
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#include <link.h>
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#include <stdlib.h>
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#include <stdio.h>
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#include <stdint.h>
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static int
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callback(struct dl_phdr_info *info, size_t size, void *data)
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{
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char *type;
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int p_type;
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printf("Name: \e"%s\e" (%d segments)\en", info\->dlpi_name,
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info\->dlpi_phnum);
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for (int j = 0; j < info\->dlpi_phnum; j++) {
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p_type = info\->dlpi_phdr[j].p_type;
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type = (p_type == PT_LOAD) ? "PT_LOAD" :
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(p_type == PT_DYNAMIC) ? "PT_DYNAMIC" :
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(p_type == PT_INTERP) ? "PT_INTERP" :
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(p_type == PT_NOTE) ? "PT_NOTE" :
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(p_type == PT_INTERP) ? "PT_INTERP" :
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(p_type == PT_PHDR) ? "PT_PHDR" :
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(p_type == PT_TLS) ? "PT_TLS" :
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(p_type == PT_GNU_EH_FRAME) ? "PT_GNU_EH_FRAME" :
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(p_type == PT_GNU_STACK) ? "PT_GNU_STACK" :
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(p_type == PT_GNU_RELRO) ? "PT_GNU_RELRO" : NULL;
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printf(" %2d: [%14p; memsz:%7jx] flags: %#jx; ", j,
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(void *) (info\->dlpi_addr + info\->dlpi_phdr[j].p_vaddr),
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(uintmax_t) info\->dlpi_phdr[j].p_memsz,
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(uintmax_t) info\->dlpi_phdr[j].p_flags);
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if (type != NULL)
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printf("%s\en", type);
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else
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printf("[other (%#x)]\en", p_type);
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}
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return 0;
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}
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int
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main(int argc, char *argv[])
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{
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dl_iterate_phdr(callback, NULL);
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exit(EXIT_SUCCESS);
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}
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.EE
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.SH SEE ALSO
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.BR ldd (1),
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.BR objdump (1),
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.BR readelf (1),
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.BR dladdr (3),
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.BR dlopen (3),
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.BR elf (5),
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.BR ld.so (8)
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.PP
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.IR "Executable and Linking Format Specification" ,
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available at various locations online.
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