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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 are 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 0. Otherwise elf was NULL or an error occurred, and the function returns -1.
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