elf_cntl(3elf)

elf_cntl -- control a file descriptor

Synopsis

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

   int elf_cntl(Elf elf, Elf_Cmd cmd);

Description

elf_cntl instructs the library to modify its behavior with respect to an ELF descriptor, elf. As elf_begin(3elf) describes, an ELF descriptor can have multiple activations, and multiple ELF descriptors may share a single file descriptor. Generally, elf_cntl commands apply to all activations of elf. Moreover, if the ELF descriptor is associated with an archive file, descriptors for members within the archive will also be affected as described below. Unless stated otherwise, operations on archive members do not affect the descriptor for the containing archive.

The cmd argument tells what actions to take and may have the following values.

ELF_C_FDDONE: This value tells the library not to use the file descriptor associated with elf. A program should use this command when it has requested all the information it cares to use and wishes to avoid the overhead of reading the rest of the file. The memory for all completed operations remains valid, but later file operations, such as the initial elf_getdata for a section, will fail if the data is not in memory already.
ELF_C_FDREAD: This command is similar to ELF_C_FDDONE, except it forces the library to read the rest of the file. A program should use this command when it must close the file descriptor but has not yet read everything it needs from the file. After elf_cntl completes the ELF_C_FDREAD command, future operations, such as elf_getdata, will use the memory version of the file without needing to use the file descriptor.

If elf_cntl succeeds, it returns zero. Otherwise elf was null or an error occurred, and the function returns -1.

References

Intro(3elf), elf_begin(3elf), elf_getdata(3elf), elf_rawfile(3elf)

Notices

If the program wishes to use the ``raw'' operations [see elf_rawdata, which elf_getdata(3elf) describes, and elf_rawfile(3elf)] after disabling the file descriptor with ELF_C_FDDONE or ELF_C_FDREAD, it must execute the raw operations explicitly beforehand. Otherwise, the raw file operations will fail. Calling elf_rawfile makes the entire image available, thus supporting subsequent elf_rawdata calls.