elf_flag.3e (2010 09)

elf_ﬂag(3E) elf_ﬂag(3E)

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 asso-

ciated status bits, returning the updated bits. A null descriptor is allowed, to simplify error handling; all

functions return zero 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 infor-

mation 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 posi-

tions. 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

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

ehdr = elf32_getehdr(elf);

/* dirty ehdr...*/

elf_flagehdr(elf, ELF_C_SET, ELF_F_DIRTY);