elf_getscn, elf_ndxscn, elf_newscn, elf_nextscn - get section information
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);
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.
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 */
}
See attributes(7) for descriptions of the following attributes:
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elf(3ELF), elf32_getehdr(3ELF), elf32_getshdr(3ELF), elf_begin(3ELF), elf_flagdata(3ELF), elf_getdata(3ELF), libelf(3LIB), attributes(7)