man pages section 3: Extended Library Functions, Volume 1

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Updated: July 2014
 
 

elf_flagshdr(3ELF)

Name

elf_flagdata, elf_flagehdr, elf_flagelf, elf_flagphdr, elf_flagscn, elf_flagshdr - manipulate flags

Synopsis

cc [ flag ... ] file ... –lelf [ library ... ]
#include <libelf.h>

unsigned elf_flagdata(Elf_Data *data, Elf_Cmd cmd, unsigned flags);
unsigned elf_flagehdr(Elf *elf, Elf_Cmd cmd, unsigned flags);
unsigned elf_flagelf(Elf *elf, Elf_Cmd cmd, unsigned flags);
unsigned elf_flagphdr(Elf *elf, Elf_Cmd cmd, unsigned flags);
unsigned elf_flagscn(Elf_Scn *scn, Elf_Cmd cmd, unsigned flags);
unsigned elf_flagshdr(Elf_Scn *scn, Elf_Cmd cmd, unsigned flags);

Description

These functions manipulate the flags associated with various structures of an ELF file. Given an ELF descriptor (elf), a data descriptor (data), or a section descriptor (scn), the functions may set or clear the associated status bits, returning the updated bits. A null descriptor is allowed, to simplify error handling; all functions return 0 for this degenerate case.

cmd may have the following values:

ELF_C_CLR

The functions clear the bits that are asserted in flags. Only the non-zero bits in flags are cleared; zero bits do not change the status of the descriptor.

ELF_C_SET

The functions set the bits that are asserted in flags. Only the non-zero bits in flags are set; zero bits do not change the status of the descriptor.

Descriptions of the defined flags bits appear below:

ELF_F_DIRTY

When the program intends to write an ELF file, this flag asserts the associated information needs to be written to the file. Thus, for example, a program that wished to update the ELF header of an existing file would call elf_flagehdr() with this bit set in flags and cmd equal to ELF_C_SET. A later call to elf_update() would write the marked header to the file.

ELF_F_LAYOUT

Normally, the library decides how to arrange an output file. That is, it automatically decides where to place sections, how to align them in the file, etc. If this bit is set for an ELF descriptor, the program assumes responsibility for determining all file positions. This bit is meaningful only for elf_flagelf() and applies to the entire file associated with the descriptor.

When a flag bit is set for an item, it affects all the subitems as well. Thus, for example, if the program sets the ELF_F_DIRTY bit with elf_flagelf(), the entire logical file is ``dirty.''

Examples

Example 1 A sample display of calling the elf_flagdata() function.

The following fragment shows how one might mark the ELF header to be written to the output file:

/* dirty ehdr  . . . */
ehdr = elf32_getehdr(elf);
elf_flagehdr(elf, ELF_C_SET, ELF_F_DIRTY);

Attributes

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Interface Stability
Committed
MT-Level
MT-Safe

See Also

elf(3ELF), elf32_getehdr(3ELF), elf_getdata(3ELF), elf_update(3ELF), attributes(5)