//! Implement syscalls using the vDSO.
//!
//! <https://man7.org/linux/man-pages/man7/vdso.7.html>
//!
//! # Safety
//!
//! Similar to syscalls.rs, this file performs raw system calls, and sometimes
//! passes them uninitialized memory buffers. This file also calls vDSO
//! functions.
#![allow(unsafe_code)]
#![allow(clippy::missing_transmute_annotations)]

#[cfg(target_arch = "x86")]
use super::reg::{ArgReg, RetReg, SyscallNumber, A0, A1, A2, A3, A4, A5, R0};
use super::vdso;
#[cfg(target_arch = "x86")]
use core::arch::global_asm;
#[cfg(feature = "process")]
#[cfg(any(
    target_arch = "x86_64",
    target_arch = "x86",
    target_arch = "riscv64",
    target_arch = "powerpc64"
))]
use core::ffi::c_void;
use core::mem::transmute;
use core::ptr::null_mut;
use core::sync::atomic::AtomicPtr;
use core::sync::atomic::Ordering::Relaxed;
#[cfg(target_pointer_width = "32")]
#[cfg(feature = "time")]
use linux_raw_sys::general::timespec as __kernel_old_timespec;
#[cfg(any(
    all(
        feature = "process",
        any(
            target_arch = "x86_64",
            target_arch = "x86",
            target_arch = "riscv64",
            target_arch = "powerpc64"
        )
    ),
    feature = "time"
))]
use {super::c, super::conv::ret, core::mem::MaybeUninit};
#[cfg(feature = "time")]
use {
    super::conv::c_int,
    crate::clockid::{ClockId, DynamicClockId},
    crate::io,
    crate::timespec::Timespec,
    linux_raw_sys::general::{__kernel_clockid_t, __kernel_timespec},
};

#[cfg(feature = "time")]
#[inline]
pub(crate) fn clock_gettime(which_clock: ClockId) -> __kernel_timespec {
    // SAFETY: `CLOCK_GETTIME` contains either null or the address of a
    // function with an ABI like libc `clock_gettime`, and calling it has the
    // side effect of writing to the result buffer, and no others.
    unsafe {
        let mut result = MaybeUninit::<__kernel_timespec>::uninit();
        let callee = match transmute(CLOCK_GETTIME.load(Relaxed)) {
            Some(callee) => callee,
            None => init_clock_gettime(),
        };
        let r0 = callee(which_clock as c::c_int, result.as_mut_ptr());
        // The `ClockId` enum only contains clocks which never fail. It may be
        // tempting to change this to `debug_assert_eq`, however they can still
        // fail on uncommon kernel configs, so we leave this in place to ensure
        // that we don't execute undefined behavior if they ever do fail.
        assert_eq!(r0, 0);
        result.assume_init()
    }
}

#[cfg(feature = "time")]
#[inline]
pub(crate) fn clock_gettime_dynamic(which_clock: DynamicClockId<'_>) -> io::Result<Timespec> {
    let id = match which_clock {
        DynamicClockId::Known(id) => id as __kernel_clockid_t,

        DynamicClockId::Dynamic(fd) => {
            // See `FD_TO_CLOCKID` in Linux's `clock_gettime` documentation.
            use crate::backend::fd::AsRawFd;
            const CLOCKFD: i32 = 3;
            ((!fd.as_raw_fd() << 3) | CLOCKFD) as __kernel_clockid_t
        }

        DynamicClockId::RealtimeAlarm => c::CLOCK_REALTIME_ALARM as __kernel_clockid_t,
        DynamicClockId::Tai => c::CLOCK_TAI as __kernel_clockid_t,
        DynamicClockId::Boottime => c::CLOCK_BOOTTIME as __kernel_clockid_t,
        DynamicClockId::BoottimeAlarm => c::CLOCK_BOOTTIME_ALARM as __kernel_clockid_t,
    };

    // SAFETY: `CLOCK_GETTIME` contains either null or the address of a
    // function with an ABI like libc `clock_gettime`, and calling it has the
    // side effect of writing to the result buffer, and no others.
    unsafe {
        const EINVAL: c::c_int = -(c::EINVAL as c::c_int);
        let mut timespec = MaybeUninit::<Timespec>::uninit();
        let callee = match transmute(CLOCK_GETTIME.load(Relaxed)) {
            Some(callee) => callee,
            None => init_clock_gettime(),
        };
        match callee(id, timespec.as_mut_ptr()) {
            0 => (),
            EINVAL => return Err(io::Errno::INVAL),
            _ => _rustix_clock_gettime_via_syscall(id, timespec.as_mut_ptr())?,
        }
        Ok(timespec.assume_init())
    }
}

#[cfg(feature = "process")]
#[cfg(any(
    target_arch = "x86_64",
    target_arch = "x86",
    target_arch = "riscv64",
    target_arch = "powerpc64"
))]
#[inline]
pub(crate) fn sched_getcpu() -> usize {
    // SAFETY: `GETCPU` contains either null or the address of a function with
    // an ABI like libc `getcpu`, and calling it has the side effect of writing
    // to the result buffers, and no others.
    unsafe {
        let mut cpu = MaybeUninit::<u32>::uninit();
        let callee = match transmute(GETCPU.load(Relaxed)) {
            Some(callee) => callee,
            None => init_getcpu(),
        };
        let r0 = callee(cpu.as_mut_ptr(), null_mut(), null_mut());
        debug_assert_eq!(r0, 0);
        cpu.assume_init() as usize
    }
}

#[cfg(target_arch = "x86")]
pub(super) mod x86_via_vdso {
    use super::{transmute, ArgReg, Relaxed, RetReg, SyscallNumber, A0, A1, A2, A3, A4, A5, R0};
    use crate::backend::arch::asm;

    #[inline]
    pub(in crate::backend) unsafe fn syscall0(nr: SyscallNumber<'_>) -> RetReg<R0> {
        let callee = match transmute(super::SYSCALL.load(Relaxed)) {
            Some(callee) => callee,
            None => super::init_syscall(),
        };
        asm::indirect_syscall0(callee, nr)
    }

    #[inline]
    pub(in crate::backend) unsafe fn syscall1<'a>(
        nr: SyscallNumber<'a>,
        a0: ArgReg<'a, A0>,
    ) -> RetReg<R0> {
        let callee = match transmute(super::SYSCALL.load(Relaxed)) {
            Some(callee) => callee,
            None => super::init_syscall(),
        };
        asm::indirect_syscall1(callee, nr, a0)
    }

    #[inline]
    pub(in crate::backend) unsafe fn syscall1_noreturn<'a>(
        nr: SyscallNumber<'a>,
        a0: ArgReg<'a, A0>,
    ) -> ! {
        let callee = match transmute(super::SYSCALL.load(Relaxed)) {
            Some(callee) => callee,
            None => super::init_syscall(),
        };
        asm::indirect_syscall1_noreturn(callee, nr, a0)
    }

    #[inline]
    pub(in crate::backend) unsafe fn syscall2<'a>(
        nr: SyscallNumber<'a>,
        a0: ArgReg<'a, A0>,
        a1: ArgReg<'a, A1>,
    ) -> RetReg<R0> {
        let callee = match transmute(super::SYSCALL.load(Relaxed)) {
            Some(callee) => callee,
            None => super::init_syscall(),
        };
        asm::indirect_syscall2(callee, nr, a0, a1)
    }

    #[inline]
    pub(in crate::backend) unsafe fn syscall3<'a>(
        nr: SyscallNumber<'a>,
        a0: ArgReg<'a, A0>,
        a1: ArgReg<'a, A1>,
        a2: ArgReg<'a, A2>,
    ) -> RetReg<R0> {
        let callee = match transmute(super::SYSCALL.load(Relaxed)) {
            Some(callee) => callee,
            None => super::init_syscall(),
        };
        asm::indirect_syscall3(callee, nr, a0, a1, a2)
    }

    #[inline]
    pub(in crate::backend) unsafe fn syscall4<'a>(
        nr: SyscallNumber<'a>,
        a0: ArgReg<'a, A0>,
        a1: ArgReg<'a, A1>,
        a2: ArgReg<'a, A2>,
        a3: ArgReg<'a, A3>,
    ) -> RetReg<R0> {
        let callee = match transmute(super::SYSCALL.load(Relaxed)) {
            Some(callee) => callee,
            None => super::init_syscall(),
        };
        asm::indirect_syscall4(callee, nr, a0, a1, a2, a3)
    }

    #[inline]
    pub(in crate::backend) unsafe fn syscall5<'a>(
        nr: SyscallNumber<'a>,
        a0: ArgReg<'a, A0>,
        a1: ArgReg<'a, A1>,
        a2: ArgReg<'a, A2>,
        a3: ArgReg<'a, A3>,
        a4: ArgReg<'a, A4>,
    ) -> RetReg<R0> {
        let callee = match transmute(super::SYSCALL.load(Relaxed)) {
            Some(callee) => callee,
            None => super::init_syscall(),
        };
        asm::indirect_syscall5(callee, nr, a0, a1, a2, a3, a4)
    }

    #[inline]
    pub(in crate::backend) unsafe fn syscall6<'a>(
        nr: SyscallNumber<'a>,
        a0: ArgReg<'a, A0>,
        a1: ArgReg<'a, A1>,
        a2: ArgReg<'a, A2>,
        a3: ArgReg<'a, A3>,
        a4: ArgReg<'a, A4>,
        a5: ArgReg<'a, A5>,
    ) -> RetReg<R0> {
        let callee = match transmute(super::SYSCALL.load(Relaxed)) {
            Some(callee) => callee,
            None => super::init_syscall(),
        };
        asm::indirect_syscall6(callee, nr, a0, a1, a2, a3, a4, a5)
    }

    // With the indirect call, it isn't meaningful to do a separate
    // `_readonly` optimization.
    #[allow(unused_imports)]
    pub(in crate::backend) use {
        syscall0 as syscall0_readonly, syscall1 as syscall1_readonly,
        syscall2 as syscall2_readonly, syscall3 as syscall3_readonly,
        syscall4 as syscall4_readonly, syscall5 as syscall5_readonly,
        syscall6 as syscall6_readonly,
    };
}

#[cfg(feature = "time")]
type ClockGettimeType = unsafe extern "C" fn(c::c_int, *mut Timespec) -> c::c_int;

#[cfg(feature = "process")]
#[cfg(any(
    target_arch = "x86_64",
    target_arch = "x86",
    target_arch = "riscv64",
    target_arch = "powerpc64"
))]
type GetcpuType = unsafe extern "C" fn(*mut u32, *mut u32, *mut c_void) -> c::c_int;

/// The underlying syscall functions are only called from asm, using the
/// special syscall calling convention to pass arguments and return values,
/// which the signature here doesn't reflect.
#[cfg(target_arch = "x86")]
pub(super) type SyscallType = unsafe extern "C" fn();

/// Initialize `CLOCK_GETTIME` and return its value.
#[cfg(feature = "time")]
#[cold]
fn init_clock_gettime() -> ClockGettimeType {
    init();
    // SAFETY: Load the function address from static storage that we just
    // initialized.
    unsafe { transmute(CLOCK_GETTIME.load(Relaxed)) }
}

/// Initialize `GETCPU` and return its value.
#[cfg(feature = "process")]
#[cfg(any(
    target_arch = "x86_64",
    target_arch = "x86",
    target_arch = "riscv64",
    target_arch = "powerpc64"
))]
#[cold]
fn init_getcpu() -> GetcpuType {
    init();
    // SAFETY: Load the function address from static storage that we just
    // initialized.
    unsafe { transmute(GETCPU.load(Relaxed)) }
}

/// Initialize `SYSCALL` and return its value.
#[cfg(target_arch = "x86")]
#[cold]
fn init_syscall() -> SyscallType {
    init();
    // SAFETY: Load the function address from static storage that we just
    // initialized.
    unsafe { transmute(SYSCALL.load(Relaxed)) }
}

/// `AtomicPtr` can't hold a `fn` pointer, so we use a `*` pointer to this
/// placeholder type, and cast it as needed.
struct Function;
#[cfg(feature = "time")]
static CLOCK_GETTIME: AtomicPtr<Function> = AtomicPtr::new(null_mut());
#[cfg(feature = "process")]
#[cfg(any(
    target_arch = "x86_64",
    target_arch = "x86",
    target_arch = "riscv64",
    target_arch = "powerpc64"
))]
static GETCPU: AtomicPtr<Function> = AtomicPtr::new(null_mut());
#[cfg(target_arch = "x86")]
static SYSCALL: AtomicPtr<Function> = AtomicPtr::new(null_mut());

#[cfg(feature = "time")]
unsafe extern "C" fn rustix_clock_gettime_via_syscall(
    clockid: c::c_int,
    res: *mut Timespec,
) -> c::c_int {
    match _rustix_clock_gettime_via_syscall(clockid, res) {
        Ok(()) => 0,
        Err(err) => err.raw_os_error().wrapping_neg(),
    }
}

#[cfg(feature = "time")]
#[cfg(target_pointer_width = "32")]
unsafe fn _rustix_clock_gettime_via_syscall(
    clockid: c::c_int,
    res: *mut Timespec,
) -> io::Result<()> {
    let r0 = syscall!(__NR_clock_gettime64, c_int(clockid), res);
    match ret(r0) {
        Err(io::Errno::NOSYS) => _rustix_clock_gettime_via_syscall_old(clockid, res),
        otherwise => otherwise,
    }
}

#[cfg(feature = "time")]
#[cfg(target_pointer_width = "32")]
unsafe fn _rustix_clock_gettime_via_syscall_old(
    clockid: c::c_int,
    res: *mut Timespec,
) -> io::Result<()> {
    // Ordinarily `rustix` doesn't like to emulate system calls, but in the
    // case of time APIs, it's specific to Linux, specific to 32-bit
    // architectures *and* specific to old kernel versions, and it's not that
    // hard to fix up here, so that no other code needs to worry about this.
    let mut old_result = MaybeUninit::<__kernel_old_timespec>::uninit();
    let r0 = syscall!(__NR_clock_gettime, c_int(clockid), &mut old_result);
    match ret(r0) {
        Ok(()) => {
            let old_result = old_result.assume_init();
            *res = Timespec {
                tv_sec: old_result.tv_sec.into(),
                tv_nsec: old_result.tv_nsec.into(),
            };
            Ok(())
        }
        otherwise => otherwise,
    }
}

#[cfg(feature = "time")]
#[cfg(target_pointer_width = "64")]
unsafe fn _rustix_clock_gettime_via_syscall(
    clockid: c::c_int,
    res: *mut Timespec,
) -> io::Result<()> {
    ret(syscall!(__NR_clock_gettime, c_int(clockid), res))
}

#[cfg(feature = "process")]
#[cfg(any(
    target_arch = "x86_64",
    target_arch = "x86",
    target_arch = "riscv64",
    target_arch = "powerpc64"
))]
unsafe extern "C" fn rustix_getcpu_via_syscall(
    cpu: *mut u32,
    node: *mut u32,
    unused: *mut c_void,
) -> c::c_int {
    match ret(syscall!(__NR_getcpu, cpu, node, unused)) {
        Ok(()) => 0,
        Err(err) => err.raw_os_error().wrapping_neg(),
    }
}

#[cfg(target_arch = "x86")]
extern "C" {
    /// A symbol pointing to an `int 0x80` instruction. This “function” is only
    /// called from assembly, and only with the x86 syscall calling convention,
    /// so its signature here is not its true signature.
    ///
    /// This extern block and the `global_asm!` below can be replaced with
    /// `#[naked]` if it's stabilized.
    fn rustix_int_0x80();
}

#[cfg(target_arch = "x86")]
global_asm!(
    r#"
    .section    .text.rustix_int_0x80,"ax",@progbits
    .p2align    4
    .weak       rustix_int_0x80
    .hidden     rustix_int_0x80
    .type       rustix_int_0x80, @function
rustix_int_0x80:
    .cfi_startproc
    int    0x80
    ret
    .cfi_endproc
    .size rustix_int_0x80, .-rustix_int_0x80
"#
);

fn minimal_init() {
    // Store default function addresses in static storage so that if we
    // end up making any system calls while we read the vDSO, they'll work. If
    // the memory happens to already be initialized, this is redundant, but not
    // harmful.
    #[cfg(feature = "time")]
    {
        CLOCK_GETTIME
            .compare_exchange(
                null_mut(),
                rustix_clock_gettime_via_syscall as *mut Function,
                Relaxed,
                Relaxed,
            )
            .ok();
    }

    #[cfg(feature = "process")]
    #[cfg(any(
        target_arch = "x86_64",
        target_arch = "x86",
        target_arch = "riscv64",
        target_arch = "powerpc64"
    ))]
    {
        GETCPU
            .compare_exchange(
                null_mut(),
                rustix_getcpu_via_syscall as *mut Function,
                Relaxed,
                Relaxed,
            )
            .ok();
    }

    #[cfg(target_arch = "x86")]
    {
        SYSCALL
            .compare_exchange(
                null_mut(),
                rustix_int_0x80 as *mut Function,
                Relaxed,
                Relaxed,
            )
            .ok();
    }
}

fn init() {
    minimal_init();

    if let Some(vdso) = vdso::Vdso::new() {
        #[cfg(feature = "time")]
        {
            // Look up the platform-specific `clock_gettime` symbol as
            // documented [here], except on 32-bit platforms where we look up
            // the `64`-suffixed variant and fail if we don't find it.
            //
            // [here]: https://man7.org/linux/man-pages/man7/vdso.7.html
            #[cfg(target_arch = "x86_64")]
            let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_clock_gettime"));
            #[cfg(target_arch = "arm")]
            let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_clock_gettime64"));
            #[cfg(target_arch = "aarch64")]
            let ptr = vdso.sym(cstr!("LINUX_2.6.39"), cstr!("__kernel_clock_gettime"));
            #[cfg(target_arch = "x86")]
            let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_clock_gettime64"));
            #[cfg(target_arch = "riscv64")]
            let ptr = vdso.sym(cstr!("LINUX_4.15"), cstr!("__vdso_clock_gettime"));
            #[cfg(target_arch = "powerpc64")]
            let ptr = vdso.sym(cstr!("LINUX_2.6.15"), cstr!("__kernel_clock_gettime"));
            #[cfg(target_arch = "s390x")]
            let ptr = vdso.sym(cstr!("LINUX_2.6.29"), cstr!("__kernel_clock_gettime"));
            #[cfg(any(target_arch = "mips", target_arch = "mips32r6"))]
            let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_clock_gettime64"));
            #[cfg(any(target_arch = "mips64", target_arch = "mips64r6"))]
            let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_clock_gettime"));

            // On all 64-bit platforms, the 64-bit `clock_gettime` symbols are
            // always available.
            #[cfg(target_pointer_width = "64")]
            let ok = true;

            // On some 32-bit platforms, the 64-bit `clock_gettime` symbols are
            // not available on older kernel versions.
            #[cfg(any(
                target_arch = "arm",
                target_arch = "mips",
                target_arch = "mips32r6",
                target_arch = "x86"
            ))]
            let ok = !ptr.is_null();

            if ok {
                assert!(!ptr.is_null());

                // Store the computed function addresses in static storage so
                // that we don't need to compute them again (but if we do, it
                // doesn't hurt anything).
                CLOCK_GETTIME.store(ptr.cast(), Relaxed);
            }
        }

        #[cfg(feature = "process")]
        #[cfg(any(
            target_arch = "x86_64",
            target_arch = "x86",
            target_arch = "riscv64",
            target_arch = "powerpc64"
        ))]
        {
            // Look up the platform-specific `getcpu` symbol as documented
            // [here].
            //
            // [here]: https://man7.org/linux/man-pages/man7/vdso.7.html
            #[cfg(target_arch = "x86_64")]
            let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_getcpu"));
            #[cfg(target_arch = "x86")]
            let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_getcpu"));
            #[cfg(target_arch = "riscv64")]
            let ptr = vdso.sym(cstr!("LINUX_4.15"), cstr!("__kernel_getcpu"));
            #[cfg(target_arch = "powerpc64")]
            let ptr = vdso.sym(cstr!("LINUX_2.6.15"), cstr!("__kernel_getcpu"));

            #[cfg(any(
                target_arch = "x86_64",
                target_arch = "riscv64",
                target_arch = "powerpc64"
            ))]
            let ok = true;

            // On 32-bit x86, the symbol doesn't appear present sometimes.
            #[cfg(target_arch = "x86")]
            let ok = !ptr.is_null();

            #[cfg(any(
                target_arch = "aarch64",
                target_arch = "arm",
                target_arch = "mips",
                target_arch = "mips32r6",
                target_arch = "mips64",
                target_arch = "mips64r6",
                target_arch = "s390x",
            ))]
            let ok = false;

            if ok {
                assert!(!ptr.is_null());

                // Store the computed function addresses in static storage so
                // that we don't need to compute them again (but if we do, it
                // doesn't hurt anything).
                GETCPU.store(ptr.cast(), Relaxed);
            }
        }

        // On x86, also look up the vsyscall entry point.
        #[cfg(target_arch = "x86")]
        {
            let ptr = vdso.sym(cstr!("LINUX_2.5"), cstr!("__kernel_vsyscall"));
            assert!(!ptr.is_null());

            // As above, store the computed function addresses in
            // static storage.
            SYSCALL.store(ptr.cast(), Relaxed);
        }
    }
}
