semihosting 0.1.25

Semihosting for AArch64, Arm, RISC-V, LoongArch, MIPS32, MIPS64, and Xtensa.
Documentation 
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// SPDX-License-Identifier: Apache-2.0 OR MIT

use core::ffi::CStr;

use super::{OpenMode, sys_flen, sys_open, sys_seek};
pub(crate) use super::{sys_remove as unlink, sys_rename as rename};
use crate::{
    fd::{BorrowedFd, OwnedFd},
    fs, io,
};

pub(crate) struct Metadata {
    size: u64,
}

impl Metadata {
    #[inline]
    pub(crate) fn size(&self) -> u64 {
        self.size
    }
}

pub(crate) fn metadata(fd: BorrowedFd<'_>) -> io::Result<Metadata> {
    Ok(Metadata { size: sys_flen(fd)? as u64 })
}

pub(crate) fn open(path: &CStr, options: &fs::OpenOptions) -> io::Result<OwnedFd> {
    match (options.write, options.append) {
        (true, false) => {}
        (false, false) => {
            if options.truncate || options.create {
                return Err(io::Error::EINVAL);
            }
        }
        (_, true) => {
            if options.truncate {
                return Err(io::Error::EINVAL);
            }
        }
    }
    // Refs: https://github.com/openocd-org/openocd/blob/HEAD/src/target/semihosting_common.c
    let mode = match (options.read, options.write, options.append, options.create, options.truncate)
    {
        (true, false, false, false, false) => OpenMode::RDONLY_BINARY,
        (true, true, false, false, false) => OpenMode::RDWR_BINARY,
        (false, true, false, true, true) => OpenMode::WRONLY_TRUNC_BINARY,
        (true, true, false, true, true) => OpenMode::RDWR_TRUNC_BINARY,
        (false, true, true, true, false) => OpenMode::WRONLY_APPEND_BINARY,
        (true, true, true, true, false) => OpenMode::RDWR_APPEND_BINARY,
        _ => return Err(io::Error::UNSUPPORTED_PLATFORM),
    };
    sys_open(path, mode)
}

// TODO(arm_compat): Arm semihosting doesn't provide Large-file support (LFS).
#[allow(clippy::cast_possible_wrap, clippy::cast_sign_loss)]
pub(crate) fn seek(fd: BorrowedFd<'_>, pos: io::SeekFrom) -> io::Result<u64> {
    let abs_pos = match pos {
        io::SeekFrom::Start(pos) => pos,
        io::SeekFrom::End(offset) => {
            let len = sys_flen(fd)? as u64;
            let pos = (len as i64).saturating_add(offset);
            if pos.is_negative() {
                return Err(io::Error::EINVAL);
            }
            pos as u64
        } // io::SeekFrom::Current(_offset) => todo!(),
    };
    // sys_seek may succeed without this guard, but make the behavior consistent with other platforms.
    let abs_pos = isize::try_from(abs_pos).map_err(|_| io::Error::EINVAL)?;
    unsafe { sys_seek(fd, abs_pos as usize)? }
    Ok(abs_pos as u64)
}