cpu-local 0.2.0

Architecture CPU-local register capability for TGOSKits
Documentation 
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use super::*;
use crate::{
    CPU_AREA_CURRENT_CONTEXT_OFFSET, CPU_AREA_PREEMPTION_STATE_OFFSET, CPU_AREA_SELF_BASE_OFFSET,
};

const IA32_GS_BASE: u32 = 0xc000_0101;
#[cfg(feature = "tls")]
const IA32_FS_BASE: u32 = 0xc000_0100;

pub(super) const CURRENT_MODEL: ArchitectureCurrentModel = ArchitectureCurrentModel {
    linux_current: CurrentContextSource::RuntimeAnchor,
    unikernel_tls: CurrentContextSource::RuntimeAnchor,
};

pub(super) fn validate_environment() -> Result<(), CpuLocalError> {
    Ok(())
}

pub(super) unsafe fn install_cpu_base(area_base: usize, _boot_context: usize) {
    let area_base = area_base as u64;
    unsafe {
        core::arch::asm!(
            "wrmsr",
            in("ecx") IA32_GS_BASE,
            in("eax") area_base as u32,
            in("edx") (area_base >> 32) as u32,
            options(nostack, preserves_flags),
        );
    }
}

pub(super) unsafe fn read_cpu_base() -> Result<usize, CpuLocalError> {
    let area_base: usize;
    unsafe {
        core::arch::asm!(
            "mov {base}, gs:[{offset}]",
            base = out(reg) area_base,
            offset = const CPU_AREA_SELF_BASE_OFFSET,
            options(nostack, preserves_flags),
        );
    }
    Ok(area_base)
}

pub(super) unsafe fn read_current_context(_area_base: usize) -> usize {
    let current_context: usize;
    unsafe {
        core::arch::asm!(
            "mov {current}, gs:[{offset}]",
            current = out(reg) current_context,
            offset = const CPU_AREA_CURRENT_CONTEXT_OFFSET,
            options(nostack, preserves_flags, readonly),
        );
    }
    current_context
}

#[inline(always)]
pub(super) unsafe fn enter_preemption() {
    unsafe {
        core::arch::asm!(
            "inc dword ptr gs:[{offset}]",
            offset = const CPU_AREA_PREEMPTION_STATE_OFFSET,
            options(nostack),
        );
    }
}

#[cfg(feature = "tls")]
pub(super) unsafe fn read_kernel_tls() -> usize {
    let low: u32;
    let high: u32;
    unsafe {
        core::arch::asm!(
            "rdmsr",
            in("ecx") IA32_FS_BASE,
            out("eax") low,
            out("edx") high,
            options(nostack, preserves_flags),
        )
    };
    ((high as usize) << 32) | low as usize
}

#[cfg(feature = "tls")]
pub(super) unsafe fn write_kernel_tls(value: usize) {
    let value = value as u64;
    unsafe {
        core::arch::asm!(
            "wrmsr",
            in("ecx") IA32_FS_BASE,
            in("eax") value as u32,
            in("edx") (value >> 32) as u32,
            options(nostack, preserves_flags),
        )
    };
}