man pages section 3: Extended Library Functions, Volume 1

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Updated: July 2014
 
 

elf_nextscn(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 */
}

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), elf32_getshdr(3ELF), elf_begin(3ELF), elf_flagdata(3ELF), elf_getdata(3ELF), libelf(3LIB), attributes(5)