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Diffstat (limited to 'man3/dl_iterate_phdr.3')
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diff --git a/man3/dl_iterate_phdr.3 b/man3/dl_iterate_phdr.3 new file mode 100644 index 0000000..dc15758 --- /dev/null +++ b/man3/dl_iterate_phdr.3 @@ -0,0 +1,346 @@ +'\" t +.\" Copyright (c) 2003, 2017 by Michael Kerrisk <mtk.manpages@gmail.com> +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.TH dl_iterate_phdr 3 2023-07-20 "Linux man-pages 6.05.01" +.SH NAME +dl_iterate_phdr \- walk through list of shared objects +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */" +.B #include <link.h> +.PP +.B int dl_iterate_phdr( +.BI " int (*" callback ")(struct dl_phdr_info *" info , +.BI " size_t " size ", void *" data ), +.BI " void *" data ); +.fi +.SH DESCRIPTION +The +.BR dl_iterate_phdr () +function allows an application to inquire at run time to find +out which shared objects it has loaded, +and the order in which they were loaded. +.PP +The +.BR dl_iterate_phdr () +function walks through the list of an +application's shared objects and calls the function +.I callback +once for each object, +until either all shared objects have been processed or +.I callback +returns a nonzero value. +.PP +Each call to +.I callback +receives three arguments: +.IR info , +which is a pointer to a structure containing information +about the shared object; +.IR size , +which is the size of the structure pointed to by +.IR info ; +and +.IR data , +which is a copy of whatever value was passed by the calling +program as the second argument (also named +.IR data ) +in the call to +.BR dl_iterate_phdr (). +.PP +The +.I info +argument is a structure of the following type: +.PP +.in +4n +.EX +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 \fIdlpi_phdr\fP */ +\& + /* The following fields were added in glibc 2.4, after the first + version of this structure was available. Check the \fIsize\fP + argument passed to the dl_iterate_phdr callback to determine + whether or not each later member is available. */ +\& + unsigned long long dlpi_adds; + /* Incremented when a new object may + have been added */ + unsigned long long dlpi_subs; + /* Incremented when an object may + have been removed */ + size_t dlpi_tls_modid; + /* If there is a PT_TLS segment, its module + ID as used in TLS relocations, else zero */ + void *dlpi_tls_data; + /* The address of the calling thread\[aq]s instance + of this module\[aq]s PT_TLS segment, if it has + one and it has been allocated in the calling + thread, otherwise a null pointer */ +}; +.EE +.in +.PP +(The +.IR 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, +.I ElfW(Addr) +yields the data type name +.IR Elf32_Addr . +Further information on these types can be found in the +.IR <elf.h> " and " <link.h> +header files.) +.PP +The +.I 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 +.I dlpi_name +field is a null-terminated string giving the pathname +from which the shared object was loaded. +.PP +To understand the meaning of the +.I dlpi_phdr +and +.I 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 +.I dlpi_phdr +field is a pointer to an array of the program headers for this +shared object. +The +.I dlpi_phnum +field indicates the size of this array. +.PP +These program headers are structures of the following form: +.PP +.in +4n +.EX +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; +.EE +.in +.PP +Note that we can calculate the location of a particular program header, +.IR x , +in virtual memory using the formula: +.PP +.in +4n +.EX +addr == info\->dlpi_addr + info\->dlpi_phdr[x].p_vaddr; +.EE +.in +.PP +Possible values for +.I p_type +include the following (see +.I <elf.h> +for further details): +.PP +.in +4n +.EX +#define PT_LOAD 1 /* Loadable program segment */ +#define PT_DYNAMIC 2 /* Dynamic linking information */ +#define PT_INTERP 3 /* Program interpreter */ +#define PT_NOTE 4 /* Auxiliary information */ +#define PT_SHLIB 5 /* Reserved */ +#define PT_PHDR 6 /* Entry for header table itself */ +#define PT_TLS 7 /* Thread\-local storage segment */ +#define PT_GNU_EH_FRAME 0x6474e550 /* GCC .eh_frame_hdr segment */ +#define PT_GNU_STACK 0x6474e551 /* Indicates stack executability */ +.\" For PT_GNU_STACK, see http://www.airs.com/blog/archives/518 +#define PT_GNU_RELRO 0x6474e552 /* Read\-only after relocation */ +.EE +.in +.SH RETURN VALUE +The +.BR dl_iterate_phdr () +function returns whatever value was returned by the last call to +.IR callback . +.SH ATTRIBUTES +For an explanation of the terms used in this section, see +.BR attributes (7). +.TS +allbox; +lbx lb lb +l l l. +Interface Attribute Value +T{ +.na +.nh +.BR dl_iterate_phdr () +T} Thread safety MT-Safe +.TE +.sp 1 +.SH VERSIONS +Various other systems provide a version of this function, +although details of the returned +.I dl_phdr_info +structure differ. +On the BSDs and Solaris, the structure includes the fields +.IR dlpi_addr , +.IR dlpi_name , +.IR dlpi_phdr , +and +.I dlpi_phnum +in addition to other implementation-specific fields. +.PP +Future versions of the C library may add further fields to the +.I dl_phdr_info +structure; in that event, the +.I size +argument provides a mechanism for the callback function to discover +whether it is running on a system with added fields. +.SH STANDARDS +None. +.SH HISTORY +glibc 2.2.4. +.SH NOTES +The first object visited by +.I callback +is the main program. +For the main program, the +.I dlpi_name +field will be an empty string. +.SH EXAMPLES +The following program displays a list of pathnames of the +shared objects it has loaded. +For each shared object, the program lists some information +(virtual address, size, flags, and type) +for each of the objects ELF segments. +.PP +The following shell session demonstrates the output +produced by the program on an x86-64 system. +The first shared object for which output is displayed +(where the name is an empty string) +is the main program. +.PP +.in +4n +.EX +$ \fB./a.out\fP +Name: "" (9 segments) + 0: [ 0x400040; memsz: 1f8] flags: 0x5; PT_PHDR + 1: [ 0x400238; memsz: 1c] flags: 0x4; PT_INTERP + 2: [ 0x400000; memsz: ac4] flags: 0x5; PT_LOAD + 3: [ 0x600e10; memsz: 240] flags: 0x6; PT_LOAD + 4: [ 0x600e28; memsz: 1d0] flags: 0x6; PT_DYNAMIC + 5: [ 0x400254; memsz: 44] flags: 0x4; PT_NOTE + 6: [ 0x400970; memsz: 3c] flags: 0x4; PT_GNU_EH_FRAME + 7: [ (nil); memsz: 0] flags: 0x6; PT_GNU_STACK + 8: [ 0x600e10; memsz: 1f0] flags: 0x4; PT_GNU_RELRO +Name: "linux\-vdso.so.1" (4 segments) + 0: [0x7ffc6edd1000; memsz: e89] flags: 0x5; PT_LOAD + 1: [0x7ffc6edd1360; memsz: 110] flags: 0x4; PT_DYNAMIC + 2: [0x7ffc6edd17b0; memsz: 3c] flags: 0x4; PT_NOTE + 3: [0x7ffc6edd17ec; memsz: 3c] flags: 0x4; PT_GNU_EH_FRAME +Name: "/lib64/libc.so.6" (10 segments) + 0: [0x7f55712ce040; memsz: 230] flags: 0x5; PT_PHDR + 1: [0x7f557145b980; memsz: 1c] flags: 0x4; PT_INTERP + 2: [0x7f55712ce000; memsz: 1b6a5c] flags: 0x5; PT_LOAD + 3: [0x7f55716857a0; memsz: 9240] flags: 0x6; PT_LOAD + 4: [0x7f5571688b80; memsz: 1f0] flags: 0x6; PT_DYNAMIC + 5: [0x7f55712ce270; memsz: 44] flags: 0x4; PT_NOTE + 6: [0x7f55716857a0; memsz: 78] flags: 0x4; PT_TLS + 7: [0x7f557145b99c; memsz: 544c] flags: 0x4; PT_GNU_EH_FRAME + 8: [0x7f55712ce000; memsz: 0] flags: 0x6; PT_GNU_STACK + 9: [0x7f55716857a0; memsz: 3860] flags: 0x4; PT_GNU_RELRO +Name: "/lib64/ld\-linux\-x86\-64.so.2" (7 segments) + 0: [0x7f557168f000; memsz: 20828] flags: 0x5; PT_LOAD + 1: [0x7f55718afba0; memsz: 15a8] flags: 0x6; PT_LOAD + 2: [0x7f55718afe10; memsz: 190] flags: 0x6; PT_DYNAMIC + 3: [0x7f557168f1c8; memsz: 24] flags: 0x4; PT_NOTE + 4: [0x7f55716acec4; memsz: 604] flags: 0x4; PT_GNU_EH_FRAME + 5: [0x7f557168f000; memsz: 0] flags: 0x6; PT_GNU_STACK + 6: [0x7f55718afba0; memsz: 460] flags: 0x4; PT_GNU_RELRO +.EE +.in +.SS Program source +\& +.\" SRC BEGIN (dl_iterate_phdr.c) +.EX +#define _GNU_SOURCE +#include <link.h> +#include <stdint.h> +#include <stdio.h> +#include <stdlib.h> +\& +static int +callback(struct dl_phdr_info *info, size_t size, void *data) +{ + char *type; + int p_type; +\& + printf("Name: \e"%s\e" (%d segments)\en", info\->dlpi_name, + info\->dlpi_phnum); +\& + for (size_t j = 0; j < info\->dlpi_phnum; j++) { + p_type = info\->dlpi_phdr[j].p_type; + type = (p_type == PT_LOAD) ? "PT_LOAD" : + (p_type == PT_DYNAMIC) ? "PT_DYNAMIC" : + (p_type == PT_INTERP) ? "PT_INTERP" : + (p_type == PT_NOTE) ? "PT_NOTE" : + (p_type == PT_INTERP) ? "PT_INTERP" : + (p_type == PT_PHDR) ? "PT_PHDR" : + (p_type == PT_TLS) ? "PT_TLS" : + (p_type == PT_GNU_EH_FRAME) ? "PT_GNU_EH_FRAME" : + (p_type == PT_GNU_STACK) ? "PT_GNU_STACK" : + (p_type == PT_GNU_RELRO) ? "PT_GNU_RELRO" : NULL; +\& + printf(" %2zu: [%14p; memsz:%7jx] flags: %#jx; ", j, + (void *) (info\->dlpi_addr + info\->dlpi_phdr[j].p_vaddr), + (uintmax_t) info\->dlpi_phdr[j].p_memsz, + (uintmax_t) info\->dlpi_phdr[j].p_flags); + if (type != NULL) + printf("%s\en", type); + else + printf("[other (%#x)]\en", p_type); + } +\& + return 0; +} +\& +int +main(void) +{ + dl_iterate_phdr(callback, NULL); +\& + exit(EXIT_SUCCESS); +} +.EE +.\" SRC END +.SH SEE ALSO +.BR ldd (1), +.BR objdump (1), +.BR readelf (1), +.BR dladdr (3), +.BR dlopen (3), +.BR elf (5), +.BR ld.so (8) +.PP +.IR "Executable and Linking Format Specification" , +available at various locations online. |