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//! Processor state stored in the RFLAGS register.
#[cfg(all(feature = "instructions", target_arch = "x86_64"))]
pub use self::x86_64::*;
use bitflags::bitflags;
bitflags! {
/// The RFLAGS register. All bit patterns are valid representations for this type.
#[repr(transparent)]
#[derive(PartialEq, Eq, PartialOrd, Ord, Hash, Debug, Clone, Copy)]
pub struct RFlags: u64 {
/// Processor feature identification flag.
///
/// If this flag is modifiable, the CPU supports CPUID.
const ID = 1 << 21;
/// Indicates that an external, maskable interrupt is pending.
///
/// Used when virtual-8086 mode extensions (CR4.VME) or protected-mode virtual
/// interrupts (CR4.PVI) are activated.
const VIRTUAL_INTERRUPT_PENDING = 1 << 20;
/// Virtual image of the INTERRUPT_FLAG bit.
///
/// Used when virtual-8086 mode extensions (CR4.VME) or protected-mode virtual
/// interrupts (CR4.PVI) are activated.
const VIRTUAL_INTERRUPT = 1 << 19;
/// Enable automatic alignment checking if CR0.AM is set. Only works if CPL is 3.
const ALIGNMENT_CHECK = 1 << 18;
/// Enable the virtual-8086 mode.
const VIRTUAL_8086_MODE = 1 << 17;
/// Allows to restart an instruction following an instruction breakpoint.
const RESUME_FLAG = 1 << 16;
/// Used by `iret` in hardware task switch mode to determine if current task is nested.
const NESTED_TASK = 1 << 14;
/// The high bit of the I/O Privilege Level field.
///
/// Specifies the privilege level required for executing I/O address-space instructions.
const IOPL_HIGH = 1 << 13;
/// The low bit of the I/O Privilege Level field.
///
/// Specifies the privilege level required for executing I/O address-space instructions.
const IOPL_LOW = 1 << 12;
/// Set by hardware to indicate that the sign bit of the result of the last signed integer
/// operation differs from the source operands.
const OVERFLOW_FLAG = 1 << 11;
/// Determines the order in which strings are processed.
const DIRECTION_FLAG = 1 << 10;
/// Enable interrupts.
const INTERRUPT_FLAG = 1 << 9;
/// Enable single-step mode for debugging.
const TRAP_FLAG = 1 << 8;
/// Set by hardware if last arithmetic operation resulted in a negative value.
const SIGN_FLAG = 1 << 7;
/// Set by hardware if last arithmetic operation resulted in a zero value.
const ZERO_FLAG = 1 << 6;
/// Set by hardware if last arithmetic operation generated a carry ouf of bit 3 of the
/// result.
const AUXILIARY_CARRY_FLAG = 1 << 4;
/// Set by hardware if last result has an even number of 1 bits (only for some operations).
const PARITY_FLAG = 1 << 2;
/// Set by hardware if last arithmetic operation generated a carry out of the
/// most-significant bit of the result.
const CARRY_FLAG = 1;
}
}
#[cfg(all(feature = "instructions", target_arch = "x86_64"))]
mod x86_64 {
use super::*;
use core::arch::asm;
/// Returns the current value of the RFLAGS register.
///
/// Drops any unknown bits.
#[inline]
pub fn read() -> RFlags {
RFlags::from_bits_truncate(read_raw())
}
/// Returns the raw current value of the RFLAGS register.
#[inline]
pub fn read_raw() -> u64 {
let r: u64;
unsafe {
asm!("pushfq; pop {}", out(reg) r, options(nomem, preserves_flags));
}
r
}
/// Writes the RFLAGS register, preserves reserved bits.
///
/// ## Safety
///
/// Unsafe because undefined becavior can occur if certain flags are modified. For example,
/// the `DF` flag must be unset in all Rust code. Also, modifying `CF`, `PF`, or any other
/// flags also used by Rust/LLVM can result in undefined behavior too.
#[inline]
pub unsafe fn write(flags: RFlags) {
let old_value = read_raw();
let reserved = old_value & !(RFlags::all().bits());
let new_value = reserved | flags.bits();
unsafe {
write_raw(new_value);
}
}
/// Writes the RFLAGS register.
///
/// Does not preserve any bits, including reserved bits.
///
///
/// ## Safety
///
/// Unsafe because undefined becavior can occur if certain flags are modified. For example,
/// the `DF` flag must be unset in all Rust code. Also, modifying `CF`, `PF`, or any other
/// flags also used by Rust/LLVM can result in undefined behavior too.
#[inline]
pub unsafe fn write_raw(val: u64) {
// HACK: we mark this function as preserves_flags to prevent Rust from restoring
// saved flags after the "popf" below. See above note on safety.
unsafe {
asm!("push {}; popfq", in(reg) val, options(nomem, preserves_flags));
}
}
/// Updates the RFLAGS register, preserves reserved bits.
///
/// ## Safety
///
/// Unsafe because undefined becavior can occur if certain flags are modified. For example,
/// the `DF` flag must be unset in all Rust code. Also, modifying `CF`, `PF`, or any other
/// flags also used by Rust/LLVM can result in undefined behavior too.
#[inline]
pub unsafe fn update<F>(f: F)
where
F: FnOnce(&mut RFlags),
{
let mut flags = self::read();
f(&mut flags);
unsafe {
self::write(flags);
}
}
#[cfg(test)]
mod test {
use crate::registers::rflags::read;
#[test]
fn rflags_read() {
let rflags = read();
println!("{:#?}", rflags);
}
}
}