use std::ffi::OsStr;
use std::str;

use rustc_middle::ty::layout::LayoutOf;
use rustc_span::Symbol;
use rustc_target::abi::{Align, Size};
use rustc_target::spec::abi::Abi;

use crate::shims::alloc::EvalContextExt as _;
use crate::shims::unix::*;
use crate::*;
use shims::foreign_items::EmulateForeignItemResult;

use shims::unix::freebsd::foreign_items as freebsd;
use shims::unix::linux::foreign_items as linux;
use shims::unix::macos::foreign_items as macos;

fn is_dyn_sym(name: &str, target_os: &str) -> bool {
    match name {
        // Used for tests.
        "isatty" => true,
        // `signal` is set up as a weak symbol in `init_extern_statics` (on Android) so we might as
        // well allow it in `dlsym`.
        "signal" => true,
        // needed at least on macOS to avoid file-based fallback in getrandom
        "getentropy" => true,
        // Give specific OSes a chance to allow their symbols.
        _ =>
            match target_os {
                "freebsd" => freebsd::is_dyn_sym(name),
                "linux" => linux::is_dyn_sym(name),
                "macos" => macos::is_dyn_sym(name),
                _ => false,
            },
    }
}

impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriInterpCx<'mir, 'tcx> {}
pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
    fn emulate_foreign_item_inner(
        &mut self,
        link_name: Symbol,
        abi: Abi,
        args: &[OpTy<'tcx, Provenance>],
        dest: &MPlaceTy<'tcx, Provenance>,
    ) -> InterpResult<'tcx, EmulateForeignItemResult> {
        let this = self.eval_context_mut();

        // See `fn emulate_foreign_item_inner` in `shims/foreign_items.rs` for the general pattern.
        #[rustfmt::skip]
        match link_name.as_str() {
            // Environment variables
            "getenv" => {
                let [name] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.getenv(name)?;
                this.write_pointer(result, dest)?;
            }
            "unsetenv" => {
                let [name] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.unsetenv(name)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "setenv" => {
                let [name, value, overwrite] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                this.read_scalar(overwrite)?.to_i32()?;
                let result = this.setenv(name, value)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "getcwd" => {
                let [buf, size] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.getcwd(buf, size)?;
                this.write_pointer(result, dest)?;
            }
            "chdir" => {
                let [path] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.chdir(path)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }

            // File descriptors
            "read" => {
                let [fd, buf, count] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let fd = this.read_scalar(fd)?.to_i32()?;
                let buf = this.read_pointer(buf)?;
                let count = this.read_target_usize(count)?;
                let result = this.read(fd, buf, count)?;
                this.write_scalar(Scalar::from_target_isize(result, this), dest)?;
            }
            "write" => {
                let [fd, buf, n] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let fd = this.read_scalar(fd)?.to_i32()?;
                let buf = this.read_pointer(buf)?;
                let count = this.read_target_usize(n)?;
                trace!("Called write({:?}, {:?}, {:?})", fd, buf, count);
                let result = this.write(fd, buf, count)?;
                // Now, `result` is the value we return back to the program.
                this.write_scalar(Scalar::from_target_isize(result, this), dest)?;
            }
            "close" => {
                let [fd] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.close(fd)?;
                this.write_scalar(result, dest)?;
            }
            "fcntl" => {
                // `fcntl` is variadic. The argument count is checked based on the first argument
                // in `this.fcntl()`, so we do not use `check_shim` here.
                this.check_abi_and_shim_symbol_clash(abi, Abi::C { unwind: false }, link_name)?;
                let result = this.fcntl(args)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }

            // File and file system access
            "open" | "open64" => {
                // `open` is variadic, the third argument is only present when the second argument has O_CREAT (or on linux O_TMPFILE, but miri doesn't support that) set
                this.check_abi_and_shim_symbol_clash(abi, Abi::C { unwind: false }, link_name)?;
                let result = this.open(args)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "unlink" => {
                let [path] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.unlink(path)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "symlink" => {
                let [target, linkpath] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.symlink(target, linkpath)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "rename" => {
                let [oldpath, newpath] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.rename(oldpath, newpath)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "mkdir" => {
                let [path, mode] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.mkdir(path, mode)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "rmdir" => {
                let [path] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.rmdir(path)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "opendir" => {
                let [name] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.opendir(name)?;
                this.write_scalar(result, dest)?;
            }
            "closedir" => {
                let [dirp] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.closedir(dirp)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "lseek64" => {
                let [fd, offset, whence] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let fd = this.read_scalar(fd)?.to_i32()?;
                let offset = this.read_scalar(offset)?.to_i64()?;
                let whence = this.read_scalar(whence)?.to_i32()?;
                let result = this.lseek64(fd, offset.into(), whence)?;
                this.write_scalar(result, dest)?;
            }
            "lseek" => {
                let [fd, offset, whence] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let fd = this.read_scalar(fd)?.to_i32()?;
                let offset = this.read_scalar(offset)?.to_int(this.libc_ty_layout("off_t").size)?;
                let whence = this.read_scalar(whence)?.to_i32()?;
                let result = this.lseek64(fd, offset, whence)?;
                this.write_scalar(result, dest)?;
            }
            "ftruncate64" => {
                let [fd, length] =
                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let fd = this.read_scalar(fd)?.to_i32()?;
                let length = this.read_scalar(length)?.to_i64()?;
                let result = this.ftruncate64(fd, length.into())?;
                this.write_scalar(result, dest)?;
            }
            "ftruncate" => {
                let [fd, length] =
                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let fd = this.read_scalar(fd)?.to_i32()?;
                let length = this.read_scalar(length)?.to_int(this.libc_ty_layout("off_t").size)?;
                let result = this.ftruncate64(fd, length)?;
                this.write_scalar(result, dest)?;
            }
            "fsync" => {
                let [fd] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.fsync(fd)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "fdatasync" => {
                let [fd] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.fdatasync(fd)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "readlink" => {
                let [pathname, buf, bufsize] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.readlink(pathname, buf, bufsize)?;
                this.write_scalar(Scalar::from_target_isize(result, this), dest)?;
            }
            "posix_fadvise" => {
                let [fd, offset, len, advice] =
                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                this.read_scalar(fd)?.to_i32()?;
                this.read_target_isize(offset)?;
                this.read_target_isize(len)?;
                this.read_scalar(advice)?.to_i32()?;
                // fadvise is only informational, we can ignore it.
                this.write_null(dest)?;
            }
            "realpath" => {
                let [path, resolved_path] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.realpath(path, resolved_path)?;
                this.write_scalar(result, dest)?;
            }
            "mkstemp" => {
                let [template] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.mkstemp(template)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }

            // Sockets
            "socketpair" => {
                let [domain, type_, protocol, sv] =
                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;

                let result = this.socketpair(domain, type_, protocol, sv)?;
                this.write_scalar(result, dest)?;
            }

            // Time
            "gettimeofday" => {
                let [tv, tz] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.gettimeofday(tv, tz)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "clock_gettime" => {
                let [clk_id, tp] =
                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.clock_gettime(clk_id, tp)?;
                this.write_scalar(result, dest)?;
            }

            // Allocation
            "posix_memalign" => {
                let [ret, align, size] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let ret = this.deref_pointer(ret)?;
                let align = this.read_target_usize(align)?;
                let size = this.read_target_usize(size)?;
                // Align must be power of 2, and also at least ptr-sized (POSIX rules).
                // But failure to adhere to this is not UB, it's an error condition.
                if !align.is_power_of_two() || align < this.pointer_size().bytes() {
                    let einval = this.eval_libc_i32("EINVAL");
                    this.write_int(einval, dest)?;
                } else {
                    if size == 0 {
                        this.write_null(&ret)?;
                    } else {
                        let ptr = this.allocate_ptr(
                            Size::from_bytes(size),
                            Align::from_bytes(align).unwrap(),
                            MiriMemoryKind::C.into(),
                        )?;
                        this.write_pointer(ptr, &ret)?;
                    }
                    this.write_null(dest)?;
                }
            }

            "mmap" => {
                let [addr, length, prot, flags, fd, offset] = this.check_shim(abi, Abi::C {unwind: false}, link_name, args)?;
                let offset = this.read_scalar(offset)?.to_int(this.libc_ty_layout("off_t").size)?;
                let ptr = this.mmap(addr, length, prot, flags, fd, offset)?;
                this.write_scalar(ptr, dest)?;
            }
            "munmap" => {
                let [addr, length] = this.check_shim(abi, Abi::C {unwind: false}, link_name, args)?;
                let result = this.munmap(addr, length)?;
                this.write_scalar(result, dest)?;
            }

            "reallocarray" => {
                // Currently this function does not exist on all Unixes, e.g. on macOS.
                if !matches!(&*this.tcx.sess.target.os, "linux" | "freebsd") {
                    throw_unsup_format!(
                        "`reallocarray` is not supported on {}",
                        this.tcx.sess.target.os
                    );
                }
                let [ptr, nmemb, size] =
                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let ptr = this.read_pointer(ptr)?;
                let nmemb = this.read_target_usize(nmemb)?;
                let size = this.read_target_usize(size)?;
                // reallocarray checks a possible overflow and returns ENOMEM
                // if that happens.
                //
                // Linux: https://www.unix.com/man-page/linux/3/reallocarray/
                // FreeBSD: https://man.freebsd.org/cgi/man.cgi?query=reallocarray
                match nmemb.checked_mul(size) {
                    None => {
                        let einval = this.eval_libc("ENOMEM");
                        this.set_last_error(einval)?;
                        this.write_null(dest)?;
                    }
                    Some(len) => {
                        let res = this.realloc(ptr, len, MiriMemoryKind::C)?;
                        this.write_pointer(res, dest)?;
                    }
                }
            }

            // Dynamic symbol loading
            "dlsym" => {
                let [handle, symbol] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                this.read_target_usize(handle)?;
                let symbol = this.read_pointer(symbol)?;
                let name = this.read_c_str(symbol)?;
                if let Ok(name) = str::from_utf8(name) && is_dyn_sym(name, &this.tcx.sess.target.os) {
                    let ptr = this.fn_ptr(FnVal::Other(DynSym::from_str(name)));
                    this.write_pointer(ptr, dest)?;
                } else {
                    this.write_null(dest)?;
                }
            }

            // Querying system information
            "sysconf" => {
                let [name] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let name = this.read_scalar(name)?.to_i32()?;
                // FIXME: Which of these are POSIX, and which are GNU/Linux?
                // At least the names seem to all also exist on macOS.
                let sysconfs: &[(&str, fn(&MiriInterpCx<'_, '_>) -> Scalar<Provenance>)] = &[
                    ("_SC_PAGESIZE", |this| Scalar::from_int(this.machine.page_size, this.pointer_size())),
                    ("_SC_NPROCESSORS_CONF", |this| Scalar::from_int(this.machine.num_cpus, this.pointer_size())),
                    ("_SC_NPROCESSORS_ONLN", |this| Scalar::from_int(this.machine.num_cpus, this.pointer_size())),
                    // 512 seems to be a reasonable default. The value is not critical, in
                    // the sense that getpwuid_r takes and checks the buffer length.
                    ("_SC_GETPW_R_SIZE_MAX", |this| Scalar::from_int(512, this.pointer_size()))
                ];
                let mut result = None;
                for &(sysconf_name, value) in sysconfs {
                    let sysconf_name = this.eval_libc_i32(sysconf_name);
                    if sysconf_name == name {
                        result = Some(value(this));
                        break;
                    }
                }
                if let Some(result) = result {
                    this.write_scalar(result, dest)?;
                } else {
                    throw_unsup_format!("unimplemented sysconf name: {}", name)
                }
            }

            // Thread-local storage
            "pthread_key_create" => {
                let [key, dtor] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let key_place = this.deref_pointer_as(key, this.libc_ty_layout("pthread_key_t"))?;
                let dtor = this.read_pointer(dtor)?;

                // Extract the function type out of the signature (that seems easier than constructing it ourselves).
                let dtor = if !this.ptr_is_null(dtor)? {
                    Some(this.get_ptr_fn(dtor)?.as_instance()?)
                } else {
                    None
                };

                // Figure out how large a pthread TLS key actually is.
                // To this end, deref the argument type. This is `libc::pthread_key_t`.
                let key_type = key.layout.ty
                    .builtin_deref(true)
                    .ok_or_else(|| err_ub_format!(
                        "wrong signature used for `pthread_key_create`: first argument must be a raw pointer."
                    ))?
                    .ty;
                let key_layout = this.layout_of(key_type)?;

                // Create key and write it into the memory where `key_ptr` wants it.
                let key = this.machine.tls.create_tls_key(dtor, key_layout.size)?;
                this.write_scalar(Scalar::from_uint(key, key_layout.size), &key_place)?;

                // Return success (`0`).
                this.write_null(dest)?;
            }
            "pthread_key_delete" => {
                let [key] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let key = this.read_scalar(key)?.to_bits(key.layout.size)?;
                this.machine.tls.delete_tls_key(key)?;
                // Return success (0)
                this.write_null(dest)?;
            }
            "pthread_getspecific" => {
                let [key] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let key = this.read_scalar(key)?.to_bits(key.layout.size)?;
                let active_thread = this.get_active_thread();
                let ptr = this.machine.tls.load_tls(key, active_thread, this)?;
                this.write_scalar(ptr, dest)?;
            }
            "pthread_setspecific" => {
                let [key, new_ptr] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let key = this.read_scalar(key)?.to_bits(key.layout.size)?;
                let active_thread = this.get_active_thread();
                let new_data = this.read_scalar(new_ptr)?;
                this.machine.tls.store_tls(key, active_thread, new_data, &*this.tcx)?;

                // Return success (`0`).
                this.write_null(dest)?;
            }

            // Synchronization primitives
            "pthread_mutexattr_init" => {
                let [attr] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_mutexattr_init(attr)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_mutexattr_settype" => {
                let [attr, kind] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_mutexattr_settype(attr, kind)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_mutexattr_destroy" => {
                let [attr] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_mutexattr_destroy(attr)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_mutex_init" => {
                let [mutex, attr] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_mutex_init(mutex, attr)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_mutex_lock" => {
                let [mutex] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_mutex_lock(mutex)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_mutex_trylock" => {
                let [mutex] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_mutex_trylock(mutex)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_mutex_unlock" => {
                let [mutex] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_mutex_unlock(mutex)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_mutex_destroy" => {
                let [mutex] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_mutex_destroy(mutex)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_rwlock_rdlock" => {
                let [rwlock] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_rwlock_rdlock(rwlock)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_rwlock_tryrdlock" => {
                let [rwlock] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_rwlock_tryrdlock(rwlock)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_rwlock_wrlock" => {
                let [rwlock] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_rwlock_wrlock(rwlock)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_rwlock_trywrlock" => {
                let [rwlock] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_rwlock_trywrlock(rwlock)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_rwlock_unlock" => {
                let [rwlock] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_rwlock_unlock(rwlock)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_rwlock_destroy" => {
                let [rwlock] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_rwlock_destroy(rwlock)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_condattr_init" => {
                let [attr] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_condattr_init(attr)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_condattr_destroy" => {
                let [attr] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_condattr_destroy(attr)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_cond_init" => {
                let [cond, attr] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_cond_init(cond, attr)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_cond_signal" => {
                let [cond] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_cond_signal(cond)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_cond_broadcast" => {
                let [cond] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_cond_broadcast(cond)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_cond_wait" => {
                let [cond, mutex] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_cond_wait(cond, mutex)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_cond_timedwait" => {
                let [cond, mutex, abstime] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                this.pthread_cond_timedwait(cond, mutex, abstime, dest)?;
            }
            "pthread_cond_destroy" => {
                let [cond] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_cond_destroy(cond)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }

            // Threading
            "pthread_create" => {
                let [thread, attr, start, arg] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_create(thread, attr, start, arg)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_join" => {
                let [thread, retval] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_join(thread, retval)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_detach" => {
                let [thread] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.pthread_detach(thread)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "pthread_self" => {
                let [] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let res = this.pthread_self()?;
                this.write_scalar(res, dest)?;
            }
            "sched_yield" => {
                let [] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.sched_yield()?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "nanosleep" => {
                let [req, rem] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.nanosleep(req, rem)?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }

            // Miscellaneous
            "isatty" => {
                let [fd] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let result = this.isatty(fd)?;
                this.write_scalar(result, dest)?;
            }
            "pthread_atfork" => {
                let [prepare, parent, child] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                this.read_pointer(prepare)?;
                this.read_pointer(parent)?;
                this.read_pointer(child)?;
                // We do not support forking, so there is nothing to do here.
                this.write_null(dest)?;
            }
            "strerror_r" | "__xpg_strerror_r" => {
                let [errnum, buf, buflen] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let errnum = this.read_scalar(errnum)?;
                let buf = this.read_pointer(buf)?;
                let buflen = this.read_target_usize(buflen)?;

                let error = this.try_errnum_to_io_error(errnum)?;
                let formatted = match error {
                    Some(err) => format!("{err}"),
                    None => format!("<unknown errnum in strerror_r: {errnum}>"),
                };
                let (complete, _) = this.write_os_str_to_c_str(OsStr::new(&formatted), buf, buflen)?;
                let ret = if complete { 0 } else { this.eval_libc_i32("ERANGE") };
                this.write_int(ret, dest)?;
            }
            "getpid" => {
                let [] = this.check_shim(abi, Abi::C { unwind: false}, link_name, args)?;
                let result = this.getpid()?;
                this.write_scalar(Scalar::from_i32(result), dest)?;
            }
            "getentropy" => {
                // This function is non-standard but exists with the same signature and behavior on
                // Linux, macOS, and FreeBSD.
                if !matches!(&*this.tcx.sess.target.os, "linux" | "macos" | "freebsd") {
                    throw_unsup_format!(
                        "`getentropy` is not supported on {}",
                        this.tcx.sess.target.os
                    );
                }

                let [buf, bufsize] =
                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let buf = this.read_pointer(buf)?;
                let bufsize = this.read_target_usize(bufsize)?;

                // getentropy sets errno to EIO when the buffer size exceeds 256 bytes.
                // FreeBSD: https://man.freebsd.org/cgi/man.cgi?query=getentropy&sektion=3&format=html
                // Linux: https://man7.org/linux/man-pages/man3/getentropy.3.html
                // macOS: https://keith.github.io/xcode-man-pages/getentropy.2.html
                if bufsize > 256 {
                    let err = this.eval_libc("EIO");
                    this.set_last_error(err)?;
                    this.write_scalar(Scalar::from_i32(-1), dest)?;
                } else {
                    this.gen_random(buf, bufsize)?;
                    this.write_scalar(Scalar::from_i32(0), dest)?;
                }
            }

            // Incomplete shims that we "stub out" just to get pre-main initialization code to work.
            // These shims are enabled only when the caller is in the standard library.
            "pthread_attr_getguardsize"
            if this.frame_in_std() => {
                let [_attr, guard_size] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let guard_size = this.deref_pointer(guard_size)?;
                let guard_size_layout = this.libc_ty_layout("size_t");
                this.write_scalar(Scalar::from_uint(this.machine.page_size, guard_size_layout.size), &guard_size)?;

                // Return success (`0`).
                this.write_null(dest)?;
            }

            | "pthread_attr_init"
            | "pthread_attr_destroy"
            if this.frame_in_std() => {
                let [_] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                this.write_null(dest)?;
            }
            | "pthread_attr_setstacksize"
            if this.frame_in_std() => {
                let [_, _] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                this.write_null(dest)?;
            }

            "pthread_attr_getstack"
            if this.frame_in_std() => {
                // We don't support "pthread_attr_setstack", so we just pretend all stacks have the same values here.
                // Hence we can mostly ignore the input `attr_place`.
                let [attr_place, addr_place, size_place] =
                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                let _attr_place = this.deref_pointer_as(attr_place, this.libc_ty_layout("pthread_attr_t"))?;
                let addr_place = this.deref_pointer(addr_place)?;
                let size_place = this.deref_pointer(size_place)?;

                this.write_scalar(
                    Scalar::from_uint(this.machine.stack_addr, this.pointer_size()),
                    &addr_place,
                )?;
                this.write_scalar(
                    Scalar::from_uint(this.machine.stack_size, this.pointer_size()),
                    &size_place,
                )?;

                // Return success (`0`).
                this.write_null(dest)?;
            }

            | "signal"
            | "sigaltstack"
            if this.frame_in_std() => {
                let [_, _] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                this.write_null(dest)?;
            }
            | "sigaction"
            | "mprotect"
            if this.frame_in_std() => {
                let [_, _, _] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                this.write_null(dest)?;
            }

            "getuid"
            if this.frame_in_std() => {
                let [] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                // For now, just pretend we always have this fixed UID.
                this.write_int(super::UID, dest)?;
            }

            "getpwuid_r"
            if this.frame_in_std() => {
                let [uid, pwd, buf, buflen, result] =
                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                this.check_no_isolation("`getpwuid_r`")?;

                let uid = this.read_scalar(uid)?.to_u32()?;
                let pwd = this.deref_pointer_as(pwd, this.libc_ty_layout("passwd"))?;
                let buf = this.read_pointer(buf)?;
                let buflen = this.read_target_usize(buflen)?;
                let result = this.deref_pointer(result)?;

                // Must be for "us".
                if uid != crate::shims::unix::UID {
                    throw_unsup_format!("`getpwuid_r` on other users is not supported");
                }

                // Reset all fields to `uninit` to make sure nobody reads them.
                // (This is a std-only shim so we are okay with such hacks.)
                this.write_uninit(&pwd)?;

                // We only set the home_dir field.
                #[allow(deprecated)]
                let home_dir = std::env::home_dir().unwrap();
                let (written, _) = this.write_path_to_c_str(&home_dir, buf, buflen)?;
                let pw_dir = this.project_field_named(&pwd, "pw_dir")?;
                this.write_pointer(buf, &pw_dir)?;

                if written {
                    this.write_pointer(pwd.ptr(), &result)?;
                    this.write_null(dest)?;
                } else {
                    this.write_null(&result)?;
                    this.write_scalar(this.eval_libc("ERANGE"), dest)?;
                }
            }

            "sched_getaffinity" => {
                // FreeBSD supports it as well since 13.1 (as a wrapper of cpuset_getaffinity)
                if !matches!(&*this.tcx.sess.target.os, "linux" | "freebsd") {
                    throw_unsup_format!(
                        "`sched_getaffinity` is not supported on {}",
                        this.tcx.sess.target.os
                    );
                }
                let [pid, cpusetsize, mask] =
                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                this.read_scalar(pid)?.to_i32()?;
                this.read_target_usize(cpusetsize)?;
                this.deref_pointer_as(mask, this.libc_ty_layout("cpu_set_t"))?;
                // FIXME: we just return an error; `num_cpus` then falls back to `sysconf`.
                let einval = this.eval_libc("EINVAL");
                this.set_last_error(einval)?;
                this.write_scalar(Scalar::from_i32(-1), dest)?;
            }

            // Platform-specific shims
            _ => {
                let target_os = &*this.tcx.sess.target.os;
                return match target_os {
                    "freebsd" => freebsd::EvalContextExt::emulate_foreign_item_inner(this, link_name, abi, args, dest),
                    "linux" => linux::EvalContextExt::emulate_foreign_item_inner(this, link_name, abi, args, dest),
                    "macos" => macos::EvalContextExt::emulate_foreign_item_inner(this, link_name, abi, args, dest),
                    _ => Ok(EmulateForeignItemResult::NotSupported),
                };
            }
        };

        Ok(EmulateForeignItemResult::NeedsJumping)
    }
}