Tribblix: manual page: elf

ELF_GETSCN(3ELF) ELF Library Functions ELF_GETSCN(3ELF)

NAME

elf_getscn, elf_ndxscn, elf_newscn, elf_nextscn - get section
information

SYNOPSIS

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

Elf_Scn *elf_getscn(Elf *elf, size_t index);

size_t elf_ndxscn(Elf_Scn *scn);

Elf_Scn *elf_newscn(Elf *elf);

Elf_Scn *elf_nextscn(Elf *elf, Elf_Scn *scn);

DESCRIPTION

These functions provide indexed and sequential access to the sections
associated with the ELF descriptor elf. If the program is building a
new file, it is responsible for creating the file's ELF header before
creating sections; see elf32_getehdr(3ELF).

The elf_getscn() function returns a section descriptor, given an
index into the file's section header table. Note that the first
``real'' section has an index of 1. Although a program can get a
section descriptor for the section whose index is 0 (SHN_UNDEF, the
undefined section), the section has no data and the section header is
``empty'' (though present). If the specified section does not exist,
an error occurs, or elf is NULL, elf_getscn() returns a null pointer.

The elf_newscn() function creates a new section and appends it to the
list for elf. Because the SHN_UNDEF section is required and not
``interesting'' to applications, the library creates it
automatically. Thus the first call to elf_newscn() for an ELF
descriptor with no existing sections returns a descriptor for section
1. If an error occurs or elf is NULL, elf_newscn() returns a null
pointer.

After creating a new section descriptor, the program can use
elf32_getshdr() to retrieve the newly created, ``clean'' section
header. The new section descriptor will have no associated data (see
elf_getdata(3ELF)). When creating a new section in this way, the
library updates the e_shnum member of the ELF header and sets the
ELF_F_DIRTY bit for the section (see elf_flagdata(3ELF)). If the
program is building a new file, it is responsible for creating the
file's ELF header (see elf32_getehdr(3ELF)) before creating new
sections.

The elf_nextscn() function takes an existing section descriptor, scn,
and returns a section descriptor for the next higher section. One may
use a null scn to obtain a section descriptor for the section whose
index is 1 (skipping the section whose index is SHN_UNDEF). If no
further sections are present or an error occurs, elf_nextscn()
returns a null pointer.

The elf_ndxscn() function takes an existing section descriptor, scn,
and returns its section table index. If scn is null or an error
occurs, elf_ndxscn() returns SHN_UNDEF.

EXAMPLES

Example 1: A sample of calling elf_getscn() function.

An example of sequential access appears below. Each pass through the
loop processes the next section in the file; the loop terminates when
all sections have been processed.

scn = 0;
while ((scn = elf_nextscn(elf, scn)) != 0)
{
/* process section */
}