Daif

Daif is a term used in ARM architecture and Linux kernel development to refer to the processor state that controls masking of certain exceptions. The acronym DAIF stands for Debug, Asynchronous abort, IRQ (interrupt request), and FIQ (fast interrupt request). In ARMv8-A, these correspond to bits in the processor state that can be set to mask or cleared to unmask the associated exceptions.

In practice, a set bit in the DAIF field means that the corresponding class of interrupt or exception is currently masked and will not be handled until the bit is cleared. Conversely, clearing a bit allows that type of interrupt or exception to be serviced. The DAIF state can be read or modified through privileged instructions in assembly, such as setting or clearing the DAIF bits with dedicated operations (for example, msr or related instructions in ARM64).

The concept is mainly relevant to low-level programming, operating system kernels, and other software that runs with privileged access to the CPU. It is used to implement critical sections, interrupt handling, and context switching. In Linux on ARM architectures, saving and restoring the DAIF state is a common technique to protect critical regions from concurrent interrupts, ensuring atomicity of operations.

Daif is architecture-specific and not applicable in user-space software running on general-purpose processors. Its understanding requires familiarity with ARM processor state and privileged instruction semantics. The term may appear in kernel source code, documentation, and discussions about interrupt masking and exception handling on ARM platforms.