Auto merge of #128699 - RalfJung:miri-sync, r=RalfJung

Miri subtree update

r? `@ghost`

Author: bors

Cargo.lock

@@ -2282,6 +2282,7 @@ dependencies = [
  "smallvec",
  "tempfile",
  "ui_test 0.21.2",
+ "windows-sys 0.52.0",
 ]
 
 [[package]]
@@ -3156,9 +3157,9 @@ dependencies = [
 
 [[package]]
 name = "rustc-build-sysroot"
-version = "0.5.2"
+version = "0.5.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "fa3ca63cc537c1cb69e4c2c0afc5fda2ccd36ac84c97d5a4ae05e69b1c834afb"
+checksum = "2471f8f296262437d7e848e527b4210b44a96e53a3b4435b890227ce3e6da106"
 dependencies = [
  "anyhow",
  "rustc_version",

src/tools/miri/Cargo.lock

@@ -9,12 +9,12 @@ default-run = "miri"
 edition = "2021"
 
 [lib]
-test = true # we have unit tests
+test = true     # we have unit tests
 doctest = false # but no doc tests
 
 [[bin]]
 name = "miri"
-test = false # we have no unit tests
+test = false    # we have no unit tests
 doctest = false # and no doc tests
 
 [dependencies]
@@ -42,6 +42,13 @@ libc = "0.2"
 libffi = "3.2.0"
 libloading = "0.8"
 
+[target.'cfg(target_family = "windows")'.dependencies]
+windows-sys = { version = "0.52", features = [
+    "Win32_Foundation",
+    "Win32_System_IO",
+    "Win32_Storage_FileSystem",
+] }
+
 [dev-dependencies]
 colored = "2"
 ui_test = "0.21.1"

src/tools/miri/Cargo.toml

@@ -476,6 +476,19 @@ Miri provides some `extern` functions that programs can import to access
 Miri-specific functionality. They are declared in
 [/tests/utils/miri\_extern.rs](/tests/utils/miri_extern.rs).
 
+## Entry point for no-std binaries
+
+Binaries that do not use the standard library are expected to declare a function like this so that
+Miri knows where it is supposed to start execution:
+
+```rust
+#[cfg(miri)]
+#[no_mangle]
+fn miri_start(argc: isize, argv: *const *const u8) -> isize {
+    // Call the actual start function that your project implements, based on your target's conventions.
+}
+```
+
 ## Contributing and getting help
 
 If you want to contribute to Miri, great!  Please check out our

src/tools/miri/cargo-miri/Cargo.lock

@@ -18,7 +18,7 @@ directories = "5"
 rustc_version = "0.4"
 serde_json = "1.0.40"
 cargo_metadata = "0.18.0"
-rustc-build-sysroot = "0.5.2"
+rustc-build-sysroot = "0.5.3"
 
 # Enable some feature flags that dev-dependencies need but dependencies
 # do not.  This makes `./miri install` after `./miri build` faster.

src/tools/miri/cargo-miri/Cargo.toml

@@ -355,7 +355,10 @@ impl Command {
         let head = cmd!(sh, "git rev-parse HEAD").read()?;
         let fetch_head = cmd!(sh, "git rev-parse FETCH_HEAD").read()?;
         if head != fetch_head {
-            bail!("Josh created a non-roundtrip push! Do NOT merge this into rustc!");
+            bail!(
+                "Josh created a non-roundtrip push! Do NOT merge this into rustc!\n\
+                Expected {head}, got {fetch_head}."
+            );
         }
         println!(
             "Confirmed that the push round-trips back to Miri properly. Please create a rustc PR:"

src/tools/miri/miri-script/src/commands.rs

@@ -1 +1 @@
-a526d7ce45fd2284e0e7c7556ccba2425b9d25e5
+29e924841f06bb181d87494eba2783761bc1ddec

src/tools/miri/rust-version

@@ -14,11 +14,14 @@ extern crate tracing;
 extern crate rustc_data_structures;
 extern crate rustc_driver;
 extern crate rustc_hir;
+extern crate rustc_hir_analysis;
 extern crate rustc_interface;
 extern crate rustc_log;
 extern crate rustc_metadata;
 extern crate rustc_middle;
 extern crate rustc_session;
+extern crate rustc_span;
+extern crate rustc_target;
 
 use std::env::{self, VarError};
 use std::num::NonZero;
@@ -29,20 +32,25 @@ use tracing::debug;
 
 use rustc_data_structures::sync::Lrc;
 use rustc_driver::Compilation;
+use rustc_hir::def_id::LOCAL_CRATE;
 use rustc_hir::{self as hir, Node};
+use rustc_hir_analysis::check::check_function_signature;
 use rustc_interface::interface::Config;
 use rustc_middle::{
     middle::{
         codegen_fn_attrs::CodegenFnAttrFlags,
         exported_symbols::{ExportedSymbol, SymbolExportInfo, SymbolExportKind, SymbolExportLevel},
     },
     query::LocalCrate,
-    ty::TyCtxt,
+    traits::{ObligationCause, ObligationCauseCode},
+    ty::{self, Ty, TyCtxt},
     util::Providers,
 };
-use rustc_session::config::{CrateType, ErrorOutputType, OptLevel};
+use rustc_session::config::{CrateType, EntryFnType, ErrorOutputType, OptLevel};
 use rustc_session::search_paths::PathKind;
 use rustc_session::{CtfeBacktrace, EarlyDiagCtxt};
+use rustc_span::def_id::DefId;
+use rustc_target::spec::abi::Abi;
 
 use miri::{BacktraceStyle, BorrowTrackerMethod, ProvenanceMode, RetagFields, ValidationMode};
 
@@ -82,11 +90,7 @@ impl rustc_driver::Callbacks for MiriCompilerCalls {
                 tcx.dcx().fatal("miri only makes sense on bin crates");
             }
 
-            let (entry_def_id, entry_type) = if let Some(entry_def) = tcx.entry_fn(()) {
-                entry_def
-            } else {
-                tcx.dcx().fatal("miri can only run programs that have a main function");
-            };
+            let (entry_def_id, entry_type) = entry_fn(tcx);
             let mut config = self.miri_config.clone();
 
             // Add filename to `miri` arguments.
@@ -351,6 +355,56 @@ fn jemalloc_magic() {
     }
 }
 
+fn entry_fn(tcx: TyCtxt<'_>) -> (DefId, EntryFnType) {
+    if let Some(entry_def) = tcx.entry_fn(()) {
+        return entry_def;
+    }
+    // Look for a symbol in the local crate named `miri_start`, and treat that as the entry point.
+    let sym = tcx.exported_symbols(LOCAL_CRATE).iter().find_map(|(sym, _)| {
+        if sym.symbol_name_for_local_instance(tcx).name == "miri_start" { Some(sym) } else { None }
+    });
+    if let Some(ExportedSymbol::NonGeneric(id)) = sym {
+        let start_def_id = id.expect_local();
+        let start_span = tcx.def_span(start_def_id);
+
+        let expected_sig = ty::Binder::dummy(tcx.mk_fn_sig(
+            [tcx.types.isize, Ty::new_imm_ptr(tcx, Ty::new_imm_ptr(tcx, tcx.types.u8))],
+            tcx.types.isize,
+            false,
+            hir::Safety::Safe,
+            Abi::Rust,
+        ));
+
+        let correct_func_sig = check_function_signature(
+            tcx,
+            ObligationCause::new(start_span, start_def_id, ObligationCauseCode::Misc),
+            *id,
+            expected_sig,
+        )
+        .is_ok();
+
+        if correct_func_sig {
+            (*id, EntryFnType::Start)
+        } else {
+            tcx.dcx().fatal(
+                "`miri_start` must have the following signature:\n\
+                        fn miri_start(argc: isize, argv: *const *const u8) -> isize",
+            );
+        }
+    } else {
+        tcx.dcx().fatal(
+            "Miri can only run programs that have a main function.\n\
+            Alternatively, you can export a `miri_start` function:\n\
+            \n\
+            #[cfg(miri)]\n\
+            #[no_mangle]\n\
+            fn miri_start(argc: isize, argv: *const *const u8) -> isize {\
+            \n    // Call the actual start function that your project implements, based on your target's conventions.\n\
+            }"
+        );
+    }
+}
+
 fn main() {
     #[cfg(any(target_os = "linux", target_os = "macos"))]
     jemalloc_magic();

src/tools/miri/src/bin/miri.rs

@@ -673,7 +673,8 @@ trait EvalContextPrivExt<'tcx, 'ecx>: crate::MiriInterpCxExt<'tcx> {
             // attempt to use it for a non-zero-sized access.
             // Dangling slices are a common case here; it's valid to get their length but with raw
             // pointer tagging for example all calls to get_unchecked on them are invalid.
-            if let Ok((alloc_id, base_offset, orig_tag)) = this.ptr_try_get_alloc_id(place.ptr(), 0) {
+            if let Ok((alloc_id, base_offset, orig_tag)) = this.ptr_try_get_alloc_id(place.ptr(), 0)
+            {
                 log_creation(this, Some((alloc_id, base_offset, orig_tag)))?;
                 // Still give it the new provenance, it got retagged after all.
                 return Ok(Some(Provenance::Concrete { alloc_id, tag: new_tag }));

src/tools/miri/src/borrow_tracker/stacked_borrows/mod.rs

@@ -932,7 +932,10 @@ impl<'tcx> Machine<'tcx> for MiriMachine<'tcx> {
         ecx.machine.validation != ValidationMode::No
     }
     #[inline(always)]
-    fn enforce_validity_recursively(ecx: &InterpCx<'tcx, Self>, _layout: TyAndLayout<'tcx>) -> bool {
+    fn enforce_validity_recursively(
+        ecx: &InterpCx<'tcx, Self>,
+        _layout: TyAndLayout<'tcx>,
+    ) -> bool {
         ecx.machine.validation == ValidationMode::Deep
     }
 

src/tools/miri/src/machine.rs

@@ -93,7 +93,11 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         Ok(Scalar::from_i32(0))
     }
 
-    fn gettimeofday(&mut self, tv_op: &OpTy<'tcx>, tz_op: &OpTy<'tcx>) -> InterpResult<'tcx, i32> {
+    fn gettimeofday(
+        &mut self,
+        tv_op: &OpTy<'tcx>,
+        tz_op: &OpTy<'tcx>,
+    ) -> InterpResult<'tcx, Scalar> {
         let this = self.eval_context_mut();
 
         this.assert_target_os_is_unix("gettimeofday");
@@ -106,7 +110,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         if !this.ptr_is_null(tz)? {
             let einval = this.eval_libc("EINVAL");
             this.set_last_error(einval)?;
-            return Ok(-1);
+            return Ok(Scalar::from_i32(-1));
         }
 
         let duration = system_time_to_duration(&SystemTime::now())?;
@@ -115,7 +119,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 
         this.write_int_fields(&[tv_sec.into(), tv_usec.into()], &tv)?;
 
-        Ok(0)
+        Ok(Scalar::from_i32(0))
     }
 
     // The localtime() function shall convert the time in seconds since the Epoch pointed to by
@@ -308,7 +312,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         &mut self,
         req_op: &OpTy<'tcx>,
         _rem: &OpTy<'tcx>, // Signal handlers are not supported, so rem will never be written to.
-    ) -> InterpResult<'tcx, i32> {
+    ) -> InterpResult<'tcx, Scalar> {
         let this = self.eval_context_mut();
 
         this.assert_target_os_is_unix("nanosleep");
@@ -320,7 +324,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             None => {
                 let einval = this.eval_libc("EINVAL");
                 this.set_last_error(einval)?;
-                return Ok(-1);
+                return Ok(Scalar::from_i32(-1));
             }
         };
 
@@ -333,7 +337,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 @timeout = |_this| { Ok(()) }
             ),
         );
-        Ok(0)
+        Ok(Scalar::from_i32(0))
     }
 
     #[allow(non_snake_case)]

src/tools/miri/src/shims/time.rs

@@ -81,8 +81,10 @@ impl<'tcx> UnixEnvVars<'tcx> {
             return Ok(None);
         };
         // The offset is used to strip the "{name}=" part of the string.
-        let var_ptr = var_ptr
-            .wrapping_offset(Size::from_bytes(u64::try_from(name.len()).unwrap().strict_add(1)), ecx);
+        let var_ptr = var_ptr.wrapping_offset(
+            Size::from_bytes(u64::try_from(name.len()).unwrap().strict_add(1)),
+            ecx,
+        );
         Ok(Some(var_ptr))
     }
 
@@ -148,7 +150,11 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         Ok(var_ptr.unwrap_or_else(Pointer::null))
     }
 
-    fn setenv(&mut self, name_op: &OpTy<'tcx>, value_op: &OpTy<'tcx>) -> InterpResult<'tcx, i32> {
+    fn setenv(
+        &mut self,
+        name_op: &OpTy<'tcx>,
+        value_op: &OpTy<'tcx>,
+    ) -> InterpResult<'tcx, Scalar> {
         let this = self.eval_context_mut();
         this.assert_target_os_is_unix("setenv");
 
@@ -169,16 +175,16 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 this.deallocate_ptr(var, None, MiriMemoryKind::Runtime.into())?;
             }
             this.update_environ()?;
-            Ok(0) // return zero on success
+            Ok(Scalar::from_i32(0)) // return zero on success
         } else {
             // name argument is a null pointer, points to an empty string, or points to a string containing an '=' character.
             let einval = this.eval_libc("EINVAL");
             this.set_last_error(einval)?;
-            Ok(-1)
+            Ok(Scalar::from_i32(-1))
         }
     }
 
-    fn unsetenv(&mut self, name_op: &OpTy<'tcx>) -> InterpResult<'tcx, i32> {
+    fn unsetenv(&mut self, name_op: &OpTy<'tcx>) -> InterpResult<'tcx, Scalar> {
         let this = self.eval_context_mut();
         this.assert_target_os_is_unix("unsetenv");
 
@@ -195,12 +201,12 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 this.deallocate_ptr(var, None, MiriMemoryKind::Runtime.into())?;
             }
             this.update_environ()?;
-            Ok(0)
+            Ok(Scalar::from_i32(0))
         } else {
             // name argument is a null pointer, points to an empty string, or points to a string containing an '=' character.
             let einval = this.eval_libc("EINVAL");
             this.set_last_error(einval)?;
-            Ok(-1)
+            Ok(Scalar::from_i32(-1))
         }
     }
 
@@ -232,7 +238,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         Ok(Pointer::null())
     }
 
-    fn chdir(&mut self, path_op: &OpTy<'tcx>) -> InterpResult<'tcx, i32> {
+    fn chdir(&mut self, path_op: &OpTy<'tcx>) -> InterpResult<'tcx, Scalar> {
         let this = self.eval_context_mut();
         this.assert_target_os_is_unix("chdir");
 
@@ -242,16 +248,11 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             this.reject_in_isolation("`chdir`", reject_with)?;
             this.set_last_error_from_io_error(ErrorKind::PermissionDenied.into())?;
 
-            return Ok(-1);
+            return Ok(Scalar::from_i32(-1));
         }
 
-        match env::set_current_dir(path) {
-            Ok(()) => Ok(0),
-            Err(e) => {
-                this.set_last_error_from_io_error(e)?;
-                Ok(-1)
-            }
-        }
+        let result = env::set_current_dir(path).map(|()| 0);
+        Ok(Scalar::from_i32(this.try_unwrap_io_result(result)?))
     }
 
     /// Updates the `environ` static.
@@ -270,18 +271,18 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         Ok(())
     }
 
-    fn getpid(&mut self) -> InterpResult<'tcx, i32> {
+    fn getpid(&mut self) -> InterpResult<'tcx, Scalar> {
         let this = self.eval_context_mut();
         this.assert_target_os_is_unix("getpid");
 
         // The reason we need to do this wacky of a conversion is because
         // `libc::getpid` returns an i32, however, `std::process::id()` return an u32.
         // So we un-do the conversion that stdlib does and turn it back into an i32.
-        #[allow(clippy::cast_possible_wrap)]
-        Ok(this.get_pid() as i32)
+        // In `Scalar` representation, these are the same, so we don't need to anything else.
+        Ok(Scalar::from_u32(this.get_pid()))
     }
 
-    fn linux_gettid(&mut self) -> InterpResult<'tcx, i32> {
+    fn linux_gettid(&mut self) -> InterpResult<'tcx, Scalar> {
         let this = self.eval_context_ref();
         this.assert_target_os("linux", "gettid");
 
@@ -290,7 +291,6 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         // Compute a TID for this thread, ensuring that the main thread has PID == TID.
         let tid = this.get_pid().strict_add(index);
 
-        #[allow(clippy::cast_possible_wrap)]
-        Ok(tid as i32)
+        Ok(Scalar::from_u32(tid))
     }
 }

src/tools/miri/src/shims/unix/env.rs

@@ -12,6 +12,13 @@ use rustc_target::abi::Size;
 use crate::shims::unix::*;
 use crate::*;
 
+#[derive(Debug, Clone, Copy, Eq, PartialEq)]
+pub(crate) enum FlockOp {
+    SharedLock { nonblocking: bool },
+    ExclusiveLock { nonblocking: bool },
+    Unlock,
+}
+
 /// Represents an open file descriptor.
 pub trait FileDescription: std::fmt::Debug + Any {
     fn name(&self) -> &'static str;
@@ -77,6 +84,14 @@ pub trait FileDescription: std::fmt::Debug + Any {
         throw_unsup_format!("cannot close {}", self.name());
     }
 
+    fn flock<'tcx>(
+        &self,
+        _communicate_allowed: bool,
+        _op: FlockOp,
+    ) -> InterpResult<'tcx, io::Result<()>> {
+        throw_unsup_format!("cannot flock {}", self.name());
+    }
+
     fn is_tty(&self, _communicate_allowed: bool) -> bool {
         // Most FDs are not tty's and the consequence of a wrong `false` are minor,
         // so we use a default impl here.
@@ -189,9 +204,13 @@ impl FileDescription for NullOutput {
 }
 
 #[derive(Clone, Debug)]
-pub struct FileDescriptor(Rc<RefCell<Box<dyn FileDescription>>>);
+pub struct FileDescriptionRef(Rc<RefCell<Box<dyn FileDescription>>>);
+
+impl FileDescriptionRef {
+    fn new(fd: impl FileDescription) -> Self {
+        FileDescriptionRef(Rc::new(RefCell::new(Box::new(fd))))
+    }
 
-impl FileDescriptor {
     pub fn borrow(&self) -> Ref<'_, dyn FileDescription> {
         Ref::map(self.0.borrow(), |fd| fd.as_ref())
     }
@@ -213,7 +232,7 @@ impl FileDescriptor {
 /// The file descriptor table
 #[derive(Debug)]
 pub struct FdTable {
-    pub fds: BTreeMap<i32, FileDescriptor>,
+    fds: BTreeMap<i32, FileDescriptionRef>,
 }
 
 impl VisitProvenance for FdTable {
@@ -228,25 +247,25 @@ impl FdTable {
     }
     pub(crate) fn init(mute_stdout_stderr: bool) -> FdTable {
         let mut fds = FdTable::new();
-        fds.insert_fd(io::stdin());
+        fds.insert_new(io::stdin());
         if mute_stdout_stderr {
-            assert_eq!(fds.insert_fd(NullOutput), 1);
-            assert_eq!(fds.insert_fd(NullOutput), 2);
+            assert_eq!(fds.insert_new(NullOutput), 1);
+            assert_eq!(fds.insert_new(NullOutput), 2);
         } else {
-            assert_eq!(fds.insert_fd(io::stdout()), 1);
-            assert_eq!(fds.insert_fd(io::stderr()), 2);
+            assert_eq!(fds.insert_new(io::stdout()), 1);
+            assert_eq!(fds.insert_new(io::stderr()), 2);
         }
         fds
     }
 
-    /// Insert a file descriptor to the FdTable.
-    pub fn insert_fd<T: FileDescription>(&mut self, fd: T) -> i32 {
-        let file_handle = FileDescriptor(Rc::new(RefCell::new(Box::new(fd))));
-        self.insert_fd_with_min_fd(file_handle, 0)
+    /// Insert a new file description to the FdTable.
+    pub fn insert_new(&mut self, fd: impl FileDescription) -> i32 {
+        let file_handle = FileDescriptionRef::new(fd);
+        self.insert_ref_with_min_fd(file_handle, 0)
     }
 
-    /// Insert a new FD that is at least `min_fd`.
-    pub fn insert_fd_with_min_fd(&mut self, file_handle: FileDescriptor, min_fd: i32) -> i32 {
+    /// Insert a file description, giving it a file descriptor that is at least `min_fd`.
+    fn insert_ref_with_min_fd(&mut self, file_handle: FileDescriptionRef, min_fd: i32) -> i32 {
         // Find the lowest unused FD, starting from min_fd. If the first such unused FD is in
         // between used FDs, the find_map combinator will return it. If the first such unused FD
         // is after all other used FDs, the find_map combinator will return None, and we will use
@@ -282,12 +301,12 @@ impl FdTable {
         Some(fd.borrow_mut())
     }
 
-    pub fn dup(&self, fd: i32) -> Option<FileDescriptor> {
+    pub fn get_ref(&self, fd: i32) -> Option<FileDescriptionRef> {
         let fd = self.fds.get(&fd)?;
         Some(fd.clone())
     }
 
-    pub fn remove(&mut self, fd: i32) -> Option<FileDescriptor> {
+    pub fn remove(&mut self, fd: i32) -> Option<FileDescriptionRef> {
         self.fds.remove(&fd)
     }
 
@@ -298,33 +317,67 @@ impl FdTable {
 
 impl<'tcx> EvalContextExt<'tcx> for crate::MiriInterpCx<'tcx> {}
 pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
-    fn dup(&mut self, old_fd: i32) -> InterpResult<'tcx, i32> {
+    fn dup(&mut self, old_fd: i32) -> InterpResult<'tcx, Scalar> {
         let this = self.eval_context_mut();
 
-        let Some(dup_fd) = this.machine.fds.dup(old_fd) else {
-            return this.fd_not_found();
+        let Some(dup_fd) = this.machine.fds.get_ref(old_fd) else {
+            return Ok(Scalar::from_i32(this.fd_not_found()?));
         };
-        Ok(this.machine.fds.insert_fd_with_min_fd(dup_fd, 0))
+        Ok(Scalar::from_i32(this.machine.fds.insert_ref_with_min_fd(dup_fd, 0)))
     }
 
-    fn dup2(&mut self, old_fd: i32, new_fd: i32) -> InterpResult<'tcx, i32> {
+    fn dup2(&mut self, old_fd: i32, new_fd: i32) -> InterpResult<'tcx, Scalar> {
         let this = self.eval_context_mut();
 
-        let Some(dup_fd) = this.machine.fds.dup(old_fd) else {
-            return this.fd_not_found();
+        let Some(dup_fd) = this.machine.fds.get_ref(old_fd) else {
+            return Ok(Scalar::from_i32(this.fd_not_found()?));
         };
         if new_fd != old_fd {
             // Close new_fd if it is previously opened.
             // If old_fd and new_fd point to the same description, then `dup_fd` ensures we keep the underlying file description alive.
-            if let Some(file_descriptor) = this.machine.fds.fds.insert(new_fd, dup_fd) {
+            if let Some(file_description) = this.machine.fds.fds.insert(new_fd, dup_fd) {
                 // Ignore close error (not interpreter's) according to dup2() doc.
-                file_descriptor.close(this.machine.communicate())?.ok();
+                file_description.close(this.machine.communicate())?.ok();
             }
         }
-        Ok(new_fd)
+        Ok(Scalar::from_i32(new_fd))
+    }
+
+    fn flock(&mut self, fd: i32, op: i32) -> InterpResult<'tcx, Scalar> {
+        let this = self.eval_context_mut();
+        let Some(file_descriptor) = this.machine.fds.get(fd) else {
+            return Ok(Scalar::from_i32(this.fd_not_found()?));
+        };
+
+        // We need to check that there aren't unsupported options in `op`.
+        let lock_sh = this.eval_libc_i32("LOCK_SH");
+        let lock_ex = this.eval_libc_i32("LOCK_EX");
+        let lock_nb = this.eval_libc_i32("LOCK_NB");
+        let lock_un = this.eval_libc_i32("LOCK_UN");
+
+        use FlockOp::*;
+        let parsed_op = if op == lock_sh {
+            SharedLock { nonblocking: false }
+        } else if op == lock_sh | lock_nb {
+            SharedLock { nonblocking: true }
+        } else if op == lock_ex {
+            ExclusiveLock { nonblocking: false }
+        } else if op == lock_ex | lock_nb {
+            ExclusiveLock { nonblocking: true }
+        } else if op == lock_un {
+            Unlock
+        } else {
+            throw_unsup_format!("unsupported flags {:#x}", op);
+        };
+
+        let result = file_descriptor.flock(this.machine.communicate(), parsed_op)?;
+        drop(file_descriptor);
+        // return `0` if flock is successful
+        let result = result.map(|()| 0i32);
+        Ok(Scalar::from_i32(this.try_unwrap_io_result(result)?))
     }
 
-    fn fcntl(&mut self, args: &[OpTy<'tcx>]) -> InterpResult<'tcx, i32> {
+    fn fcntl(&mut self, args: &[OpTy<'tcx>]) -> InterpResult<'tcx, Scalar> {
         let this = self.eval_context_mut();
 
         if args.len() < 2 {
@@ -342,11 +395,11 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             // `FD_CLOEXEC` value without checking if the flag is set for the file because `std`
             // always sets this flag when opening a file. However we still need to check that the
             // file itself is open.
-            if this.machine.fds.is_fd(fd) {
-                Ok(this.eval_libc_i32("FD_CLOEXEC"))
+            Ok(Scalar::from_i32(if this.machine.fds.is_fd(fd) {
+                this.eval_libc_i32("FD_CLOEXEC")
             } else {
-                this.fd_not_found()
-            }
+                this.fd_not_found()?
+            }))
         } else if cmd == this.eval_libc_i32("F_DUPFD")
             || cmd == this.eval_libc_i32("F_DUPFD_CLOEXEC")
         {
@@ -362,16 +415,17 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             }
             let start = this.read_scalar(&args[2])?.to_i32()?;
 
-            match this.machine.fds.dup(fd) {
-                Some(dup_fd) => Ok(this.machine.fds.insert_fd_with_min_fd(dup_fd, start)),
-                None => this.fd_not_found(),
+            match this.machine.fds.get_ref(fd) {
+                Some(dup_fd) =>
+                    Ok(Scalar::from_i32(this.machine.fds.insert_ref_with_min_fd(dup_fd, start))),
+                None => Ok(Scalar::from_i32(this.fd_not_found()?)),
             }
         } else if this.tcx.sess.target.os == "macos" && cmd == this.eval_libc_i32("F_FULLFSYNC") {
             // Reject if isolation is enabled.
             if let IsolatedOp::Reject(reject_with) = this.machine.isolated_op {
                 this.reject_in_isolation("`fcntl`", reject_with)?;
                 this.set_last_error_from_io_error(ErrorKind::PermissionDenied.into())?;
-                return Ok(-1);
+                return Ok(Scalar::from_i32(-1));
             }
 
             this.ffullsync_fd(fd)
@@ -385,10 +439,10 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 
         let fd = this.read_scalar(fd_op)?.to_i32()?;
 
-        let Some(file_descriptor) = this.machine.fds.remove(fd) else {
+        let Some(file_description) = this.machine.fds.remove(fd) else {
             return Ok(Scalar::from_i32(this.fd_not_found()?));
         };
-        let result = file_descriptor.close(this.machine.communicate())?;
+        let result = file_description.close(this.machine.communicate())?;
         // return `0` if close is successful
         let result = result.map(|()| 0i32);
         Ok(Scalar::from_i32(this.try_unwrap_io_result(result)?))
@@ -416,7 +470,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         buf: Pointer,
         count: u64,
         offset: Option<i128>,
-    ) -> InterpResult<'tcx, i64> {
+    ) -> InterpResult<'tcx, Scalar> {
         let this = self.eval_context_mut();
 
         // Isolation check is done via `FileDescriptor` trait.
@@ -434,9 +488,9 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         let communicate = this.machine.communicate();
 
         // We temporarily dup the FD to be able to retain mutable access to `this`.
-        let Some(fd) = this.machine.fds.dup(fd) else {
+        let Some(fd) = this.machine.fds.get_ref(fd) else {
             trace!("read: FD not found");
-            return this.fd_not_found();
+            return Ok(Scalar::from_target_isize(this.fd_not_found()?, this));
         };
 
         trace!("read: FD mapped to {fd:?}");
@@ -450,7 +504,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 let Ok(offset) = u64::try_from(offset) else {
                     let einval = this.eval_libc("EINVAL");
                     this.set_last_error(einval)?;
-                    return Ok(-1);
+                    return Ok(Scalar::from_target_isize(-1, this));
                 };
                 fd.borrow_mut().pread(communicate, &mut bytes, offset, this)
             }
@@ -467,11 +521,11 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                     buf,
                     bytes[..usize::try_from(read_bytes).unwrap()].iter().copied(),
                 )?;
-                Ok(read_bytes)
+                Ok(Scalar::from_target_isize(read_bytes, this))
             }
             Err(e) => {
                 this.set_last_error_from_io_error(e)?;
-                Ok(-1)
+                Ok(Scalar::from_target_isize(-1, this))
             }
         }
     }
@@ -482,7 +536,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         buf: Pointer,
         count: u64,
         offset: Option<i128>,
-    ) -> InterpResult<'tcx, i64> {
+    ) -> InterpResult<'tcx, Scalar> {
         let this = self.eval_context_mut();
 
         // Isolation check is done via `FileDescriptor` trait.
@@ -499,8 +553,8 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 
         let bytes = this.read_bytes_ptr_strip_provenance(buf, Size::from_bytes(count))?.to_owned();
         // We temporarily dup the FD to be able to retain mutable access to `this`.
-        let Some(fd) = this.machine.fds.dup(fd) else {
-            return this.fd_not_found();
+        let Some(fd) = this.machine.fds.get_ref(fd) else {
+            return Ok(Scalar::from_target_isize(this.fd_not_found()?, this));
         };
 
         let result = match offset {
@@ -509,14 +563,14 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 let Ok(offset) = u64::try_from(offset) else {
                     let einval = this.eval_libc("EINVAL");
                     this.set_last_error(einval)?;
-                    return Ok(-1);
+                    return Ok(Scalar::from_target_isize(-1, this));
                 };
                 fd.borrow_mut().pwrite(communicate, &bytes, offset, this)
             }
         };
         drop(fd);
 
         let result = result?.map(|c| i64::try_from(c).unwrap());
-        this.try_unwrap_io_result(result)
+        Ok(Scalar::from_target_isize(this.try_unwrap_io_result(result)?, this))
     }
 }

src/tools/miri/src/shims/unix/fd.rs

@@ -64,7 +64,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             );
         }
 
-        let fd = this.machine.fds.insert_fd(Epoll::default());
+        let fd = this.machine.fds.insert_new(Epoll::default());
         Ok(Scalar::from_i32(fd))
     }
 

src/tools/miri/src/shims/unix/foreign_items.rs

@@ -178,7 +178,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             throw_unsup_format!("eventfd: encountered unknown unsupported flags {:#x}", flags);
         }
 
-        let fd = this.machine.fds.insert_fd(Event {
+        let fd = this.machine.fds.insert_new(Event {
             counter: val.into(),
             is_nonblock,
             clock: VClock::default(),

src/tools/miri/src/shims/unix/fs.rs

@@ -44,7 +44,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 let [dirfd, pathname, flags, mask, statxbuf] =
                     this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                 let result = this.linux_statx(dirfd, pathname, flags, mask, statxbuf)?;
-                this.write_scalar(Scalar::from_i32(result), dest)?;
+                this.write_scalar(result, dest)?;
             }
 
             // epoll, eventfd
@@ -97,7 +97,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             "gettid" => {
                 let [] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                 let result = this.linux_gettid()?;
-                this.write_scalar(Scalar::from_i32(result), dest)?;
+                this.write_scalar(result, dest)?;
             }
 
             // Dynamically invoked syscalls
@@ -176,12 +176,12 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             "__libc_current_sigrtmin" => {
                 let [] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 
-                this.write_scalar(Scalar::from_i32(SIGRTMIN), dest)?;
+                this.write_int(SIGRTMIN, dest)?;
             }
             "__libc_current_sigrtmax" => {
                 let [] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 
-                this.write_scalar(Scalar::from_i32(SIGRTMAX), dest)?;
+                this.write_int(SIGRTMAX, dest)?;
             }
 
             // Incomplete shims that we "stub out" just to get pre-main initialization code to work.

src/tools/miri/src/shims/unix/linux/epoll.rs

@@ -219,8 +219,8 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         };
 
         let fds = &mut this.machine.fds;
-        let sv0 = fds.insert_fd(socketpair_0);
-        let sv1 = fds.insert_fd(socketpair_1);
+        let sv0 = fds.insert_new(socketpair_0);
+        let sv1 = fds.insert_new(socketpair_1);
         let sv0 = Scalar::from_int(sv0, sv.layout.size);
         let sv1 = Scalar::from_int(sv1, sv.layout.size);
 

src/tools/miri/src/shims/unix/linux/eventfd.rs

@@ -363,20 +363,20 @@ fn cond_set_clock_id<'tcx>(
 
 impl<'tcx> EvalContextExt<'tcx> for crate::MiriInterpCx<'tcx> {}
 pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
-    fn pthread_mutexattr_init(&mut self, attr_op: &OpTy<'tcx>) -> InterpResult<'tcx, i32> {
+    fn pthread_mutexattr_init(&mut self, attr_op: &OpTy<'tcx>) -> InterpResult<'tcx, ()> {
         let this = self.eval_context_mut();
 
         let default_kind = this.eval_libc_i32("PTHREAD_MUTEX_DEFAULT");
         mutexattr_set_kind(this, attr_op, default_kind)?;
 
-        Ok(0)
+        Ok(())
     }
 
     fn pthread_mutexattr_settype(
         &mut self,
         attr_op: &OpTy<'tcx>,
         kind_op: &OpTy<'tcx>,
-    ) -> InterpResult<'tcx, i32> {
+    ) -> InterpResult<'tcx, Scalar> {
         let this = self.eval_context_mut();
 
         let kind = this.read_scalar(kind_op)?.to_i32()?;
@@ -407,13 +407,13 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             mutexattr_set_kind(this, attr_op, kind)?;
         } else {
             let einval = this.eval_libc_i32("EINVAL");
-            return Ok(einval);
+            return Ok(Scalar::from_i32(einval));
         }
 
-        Ok(0)
+        Ok(Scalar::from_i32(0))
     }
 
-    fn pthread_mutexattr_destroy(&mut self, attr_op: &OpTy<'tcx>) -> InterpResult<'tcx, i32> {
+    fn pthread_mutexattr_destroy(&mut self, attr_op: &OpTy<'tcx>) -> InterpResult<'tcx, ()> {
         let this = self.eval_context_mut();
 
         // Destroying an uninit pthread_mutexattr is UB, so check to make sure it's not uninit.
@@ -435,14 +435,14 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             &this.deref_pointer_as(attr_op, this.libc_ty_layout("pthread_mutexattr_t"))?,
         )?;
 
-        Ok(0)
+        Ok(())
     }
 
     fn pthread_mutex_init(
         &mut self,
         mutex_op: &OpTy<'tcx>,
         attr_op: &OpTy<'tcx>,
-    ) -> InterpResult<'tcx, i32> {
+    ) -> InterpResult<'tcx, ()> {
         let this = self.eval_context_mut();
 
         let attr = this.read_pointer(attr_op)?;
@@ -457,7 +457,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 
         mutex_set_kind(this, mutex_op, kind)?;
 
-        Ok(0)
+        Ok(())
     }
 
     fn pthread_mutex_lock(
@@ -501,25 +501,25 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         Ok(())
     }
 
-    fn pthread_mutex_trylock(&mut self, mutex_op: &OpTy<'tcx>) -> InterpResult<'tcx, i32> {
+    fn pthread_mutex_trylock(&mut self, mutex_op: &OpTy<'tcx>) -> InterpResult<'tcx, Scalar> {
         let this = self.eval_context_mut();
 
         let kind = mutex_get_kind(this, mutex_op)?;
         let id = mutex_get_id(this, mutex_op)?;
 
-        if this.mutex_is_locked(id) {
+        Ok(Scalar::from_i32(if this.mutex_is_locked(id) {
             let owner_thread = this.mutex_get_owner(id);
             if owner_thread != this.active_thread() {
-                Ok(this.eval_libc_i32("EBUSY"))
+                this.eval_libc_i32("EBUSY")
             } else {
                 if is_mutex_kind_default(this, kind)?
                     || is_mutex_kind_normal(this, kind)?
                     || kind == this.eval_libc_i32("PTHREAD_MUTEX_ERRORCHECK")
                 {
-                    Ok(this.eval_libc_i32("EBUSY"))
+                    this.eval_libc_i32("EBUSY")
                 } else if kind == this.eval_libc_i32("PTHREAD_MUTEX_RECURSIVE") {
                     this.mutex_lock(id);
-                    Ok(0)
+                    0
                 } else {
                     throw_unsup_format!(
                         "called pthread_mutex_trylock on an unsupported type of mutex"
@@ -529,19 +529,19 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         } else {
             // The mutex is unlocked. Let's lock it.
             this.mutex_lock(id);
-            Ok(0)
-        }
+            0
+        }))
     }
 
-    fn pthread_mutex_unlock(&mut self, mutex_op: &OpTy<'tcx>) -> InterpResult<'tcx, i32> {
+    fn pthread_mutex_unlock(&mut self, mutex_op: &OpTy<'tcx>) -> InterpResult<'tcx, Scalar> {
         let this = self.eval_context_mut();
 
         let kind = mutex_get_kind(this, mutex_op)?;
         let id = mutex_get_id(this, mutex_op)?;
 
         if let Some(_old_locked_count) = this.mutex_unlock(id)? {
             // The mutex was locked by the current thread.
-            Ok(0)
+            Ok(Scalar::from_i32(0))
         } else {
             // The mutex was locked by another thread or not locked at all. See
             // the “Unlock When Not Owner” column in
@@ -557,14 +557,14 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             } else if kind == this.eval_libc_i32("PTHREAD_MUTEX_ERRORCHECK")
                 || kind == this.eval_libc_i32("PTHREAD_MUTEX_RECURSIVE")
             {
-                Ok(this.eval_libc_i32("EPERM"))
+                Ok(Scalar::from_i32(this.eval_libc_i32("EPERM")))
             } else {
                 throw_unsup_format!("called pthread_mutex_unlock on an unsupported type of mutex");
             }
         }
     }
 
-    fn pthread_mutex_destroy(&mut self, mutex_op: &OpTy<'tcx>) -> InterpResult<'tcx, i32> {
+    fn pthread_mutex_destroy(&mut self, mutex_op: &OpTy<'tcx>) -> InterpResult<'tcx, ()> {
         let this = self.eval_context_mut();
 
         let id = mutex_get_id(this, mutex_op)?;
@@ -583,7 +583,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         )?;
         // FIXME: delete interpreter state associated with this mutex.
 
-        Ok(0)
+        Ok(())
     }
 
     fn pthread_rwlock_rdlock(
@@ -605,16 +605,16 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         Ok(())
     }
 
-    fn pthread_rwlock_tryrdlock(&mut self, rwlock_op: &OpTy<'tcx>) -> InterpResult<'tcx, i32> {
+    fn pthread_rwlock_tryrdlock(&mut self, rwlock_op: &OpTy<'tcx>) -> InterpResult<'tcx, Scalar> {
         let this = self.eval_context_mut();
 
         let id = rwlock_get_id(this, rwlock_op)?;
 
         if this.rwlock_is_write_locked(id) {
-            Ok(this.eval_libc_i32("EBUSY"))
+            Ok(Scalar::from_i32(this.eval_libc_i32("EBUSY")))
         } else {
             this.rwlock_reader_lock(id);
-            Ok(0)
+            Ok(Scalar::from_i32(0))
         }
     }
 
@@ -649,35 +649,33 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         Ok(())
     }
 
-    fn pthread_rwlock_trywrlock(&mut self, rwlock_op: &OpTy<'tcx>) -> InterpResult<'tcx, i32> {
+    fn pthread_rwlock_trywrlock(&mut self, rwlock_op: &OpTy<'tcx>) -> InterpResult<'tcx, Scalar> {
         let this = self.eval_context_mut();
 
         let id = rwlock_get_id(this, rwlock_op)?;
 
         if this.rwlock_is_locked(id) {
-            Ok(this.eval_libc_i32("EBUSY"))
+            Ok(Scalar::from_i32(this.eval_libc_i32("EBUSY")))
         } else {
             this.rwlock_writer_lock(id);
-            Ok(0)
+            Ok(Scalar::from_i32(0))
         }
     }
 
-    fn pthread_rwlock_unlock(&mut self, rwlock_op: &OpTy<'tcx>) -> InterpResult<'tcx, i32> {
+    fn pthread_rwlock_unlock(&mut self, rwlock_op: &OpTy<'tcx>) -> InterpResult<'tcx, ()> {
         let this = self.eval_context_mut();
 
         let id = rwlock_get_id(this, rwlock_op)?;
 
         #[allow(clippy::if_same_then_else)]
-        if this.rwlock_reader_unlock(id)? {
-            Ok(0)
-        } else if this.rwlock_writer_unlock(id)? {
-            Ok(0)
+        if this.rwlock_reader_unlock(id)? || this.rwlock_writer_unlock(id)? {
+            Ok(())
         } else {
             throw_ub_format!("unlocked an rwlock that was not locked by the active thread");
         }
     }
 
-    fn pthread_rwlock_destroy(&mut self, rwlock_op: &OpTy<'tcx>) -> InterpResult<'tcx, i32> {
+    fn pthread_rwlock_destroy(&mut self, rwlock_op: &OpTy<'tcx>) -> InterpResult<'tcx, ()> {
         let this = self.eval_context_mut();
 
         let id = rwlock_get_id(this, rwlock_op)?;
@@ -695,10 +693,10 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         )?;
         // FIXME: delete interpreter state associated with this rwlock.
 
-        Ok(0)
+        Ok(())
     }
 
-    fn pthread_condattr_init(&mut self, attr_op: &OpTy<'tcx>) -> InterpResult<'tcx, i32> {
+    fn pthread_condattr_init(&mut self, attr_op: &OpTy<'tcx>) -> InterpResult<'tcx, ()> {
         let this = self.eval_context_mut();
 
         // no clock attribute on macOS
@@ -710,7 +708,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             condattr_set_clock_id(this, attr_op, default_clock_id)?;
         }
 
-        Ok(0)
+        Ok(())
     }
 
     fn pthread_condattr_setclock(
@@ -737,16 +735,16 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         &mut self,
         attr_op: &OpTy<'tcx>,
         clk_id_op: &OpTy<'tcx>,
-    ) -> InterpResult<'tcx, Scalar> {
+    ) -> InterpResult<'tcx, ()> {
         let this = self.eval_context_mut();
 
         let clock_id = condattr_get_clock_id(this, attr_op)?;
         this.write_scalar(Scalar::from_i32(clock_id), &this.deref_pointer(clk_id_op)?)?;
 
-        Ok(Scalar::from_i32(0))
+        Ok(())
     }
 
-    fn pthread_condattr_destroy(&mut self, attr_op: &OpTy<'tcx>) -> InterpResult<'tcx, i32> {
+    fn pthread_condattr_destroy(&mut self, attr_op: &OpTy<'tcx>) -> InterpResult<'tcx, ()> {
         let this = self.eval_context_mut();
 
         // Destroying an uninit pthread_condattr is UB, so check to make sure it's not uninit.
@@ -761,14 +759,14 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             &this.deref_pointer_as(attr_op, this.libc_ty_layout("pthread_condattr_t"))?,
         )?;
 
-        Ok(0)
+        Ok(())
     }
 
     fn pthread_cond_init(
         &mut self,
         cond_op: &OpTy<'tcx>,
         attr_op: &OpTy<'tcx>,
-    ) -> InterpResult<'tcx, i32> {
+    ) -> InterpResult<'tcx, ()> {
         let this = self.eval_context_mut();
 
         let attr = this.read_pointer(attr_op)?;
@@ -784,21 +782,21 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 
         cond_set_clock_id(this, cond_op, clock_id)?;
 
-        Ok(0)
+        Ok(())
     }
 
-    fn pthread_cond_signal(&mut self, cond_op: &OpTy<'tcx>) -> InterpResult<'tcx, i32> {
+    fn pthread_cond_signal(&mut self, cond_op: &OpTy<'tcx>) -> InterpResult<'tcx, ()> {
         let this = self.eval_context_mut();
         let id = cond_get_id(this, cond_op)?;
         this.condvar_signal(id)?;
-        Ok(0)
+        Ok(())
     }
 
-    fn pthread_cond_broadcast(&mut self, cond_op: &OpTy<'tcx>) -> InterpResult<'tcx, i32> {
+    fn pthread_cond_broadcast(&mut self, cond_op: &OpTy<'tcx>) -> InterpResult<'tcx, ()> {
         let this = self.eval_context_mut();
         let id = cond_get_id(this, cond_op)?;
         while this.condvar_signal(id)? {}
-        Ok(0)
+        Ok(())
     }
 
     fn pthread_cond_wait(
@@ -869,7 +867,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         Ok(())
     }
 
-    fn pthread_cond_destroy(&mut self, cond_op: &OpTy<'tcx>) -> InterpResult<'tcx, i32> {
+    fn pthread_cond_destroy(&mut self, cond_op: &OpTy<'tcx>) -> InterpResult<'tcx, ()> {
         let this = self.eval_context_mut();
 
         let id = cond_get_id(this, cond_op)?;
@@ -885,6 +883,6 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         this.write_uninit(&this.deref_pointer_as(cond_op, this.libc_ty_layout("pthread_cond_t"))?)?;
         // FIXME: delete interpreter state associated with this condvar.
 
-        Ok(0)
+        Ok(())
     }
 }

src/tools/miri/src/shims/unix/linux/foreign_items.rs

@@ -10,7 +10,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         _attr: &OpTy<'tcx>,
         start_routine: &OpTy<'tcx>,
         arg: &OpTy<'tcx>,
-    ) -> InterpResult<'tcx, i32> {
+    ) -> InterpResult<'tcx, ()> {
         let this = self.eval_context_mut();
 
         let thread_info_place = this.deref_pointer_as(thread, this.libc_ty_layout("pthread_t"))?;
@@ -27,14 +27,10 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             this.layout_of(this.tcx.types.usize)?,
         )?;
 
-        Ok(0)
+        Ok(())
     }
 
-    fn pthread_join(
-        &mut self,
-        thread: &OpTy<'tcx>,
-        retval: &OpTy<'tcx>,
-    ) -> InterpResult<'tcx, i32> {
+    fn pthread_join(&mut self, thread: &OpTy<'tcx>, retval: &OpTy<'tcx>) -> InterpResult<'tcx, ()> {
         let this = self.eval_context_mut();
 
         if !this.ptr_is_null(this.read_pointer(retval)?)? {
@@ -45,10 +41,10 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         let thread_id = this.read_scalar(thread)?.to_int(this.libc_ty_layout("pthread_t").size)?;
         this.join_thread_exclusive(thread_id.try_into().expect("thread ID should fit in u32"))?;
 
-        Ok(0)
+        Ok(())
     }
 
-    fn pthread_detach(&mut self, thread: &OpTy<'tcx>) -> InterpResult<'tcx, i32> {
+    fn pthread_detach(&mut self, thread: &OpTy<'tcx>) -> InterpResult<'tcx, ()> {
         let this = self.eval_context_mut();
 
         let thread_id = this.read_scalar(thread)?.to_int(this.libc_ty_layout("pthread_t").size)?;
@@ -57,7 +53,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             /*allow_terminated_joined*/ false,
         )?;
 
-        Ok(0)
+        Ok(())
     }
 
     fn pthread_self(&mut self) -> InterpResult<'tcx, Scalar> {
@@ -113,11 +109,11 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         Ok(if success { Scalar::from_u32(0) } else { this.eval_libc("ERANGE") })
     }
 
-    fn sched_yield(&mut self) -> InterpResult<'tcx, i32> {
+    fn sched_yield(&mut self) -> InterpResult<'tcx, ()> {
         let this = self.eval_context_mut();
 
         this.yield_active_thread();
 
-        Ok(0)
+        Ok(())
     }
 }

src/tools/miri/src/shims/unix/socket.rs

@@ -197,11 +197,11 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
     }
 
     #[allow(non_snake_case)]
-    fn GetCurrentProcessId(&mut self) -> InterpResult<'tcx, u32> {
+    fn GetCurrentProcessId(&mut self) -> InterpResult<'tcx, Scalar> {
         let this = self.eval_context_mut();
         this.assert_target_os("windows", "GetCurrentProcessId");
 
-        Ok(this.get_pid())
+        Ok(Scalar::from_u32(this.get_pid()))
     }
 
     #[allow(non_snake_case)]

src/tools/miri/src/shims/unix/sync.rs

@@ -141,7 +141,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             "GetCurrentProcessId" => {
                 let [] = this.check_shim(abi, Abi::System { unwind: false }, link_name, args)?;
                 let result = this.GetCurrentProcessId()?;
-                this.write_int(result, dest)?;
+                this.write_scalar(result, dest)?;
             }
 
             // File related shims
@@ -372,7 +372,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 this.machine.tls.store_tls(key, active_thread, new_data, &*this.tcx)?;
 
                 // Return success (`1`).
-                this.write_scalar(Scalar::from_i32(1), dest)?;
+                this.write_int(1, dest)?;
             }
 
             // Access to command-line arguments
@@ -563,7 +563,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 let ptr = this.read_pointer(ptr)?;
                 let len = this.read_target_usize(len)?;
                 this.gen_random(ptr, len)?;
-                this.write_scalar(Scalar::from_i32(1), dest)?;
+                this.write_int(1, dest)?;
             }
             "BCryptGenRandom" => {
                 // used by getrandom 0.2
@@ -627,7 +627,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 
                 this.CloseHandle(handle)?;
 
-                this.write_scalar(Scalar::from_u32(1), dest)?;
+                this.write_int(1, dest)?;
             }
             "GetModuleFileNameW" => {
                 let [handle, filename, size] =

src/tools/miri/src/shims/unix/thread.rs

@@ -2,7 +2,7 @@ error: unsupported operation: returning ready events from epoll_wait is not yet
   --> CARGO_REGISTRY/.../epoll.rs:LL:CC
    |
 LL | /         syscall!(epoll_wait(
-LL | |             self.ep,
+LL | |             self.ep.as_raw_fd(),
 LL | |             events.as_mut_ptr(),
 LL | |             events.capacity() as i32,
 LL | |             timeout,

src/tools/miri/src/shims/windows/env.rs

@@ -0,0 +1,21 @@
+//@compile-flags: -Cpanic=abort
+//@error-in-other-file: `miri_start` must have the following signature:
+#![no_main]
+#![no_std]
+
+use core::fmt::Write;
+
+#[path = "../utils/mod.no_std.rs"]
+mod utils;
+
+#[no_mangle]
+fn miri_start() -> isize {
+    //~^ ERROR: mismatched types
+    writeln!(utils::MiriStdout, "Hello from miri_start!").unwrap();
+    0
+}
+
+#[panic_handler]
+fn panic_handler(_: &core::panic::PanicInfo) -> ! {
+    loop {}
+}

src/tools/miri/src/shims/windows/foreign_items.rs

@@ -0,0 +1,15 @@
+error[E0308]: mismatched types
+  --> $DIR/miri_start_wrong_sig.rs:LL:CC
+   |
+LL | fn miri_start() -> isize {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^ incorrect number of function parameters
+   |
+   = note: expected signature `fn(isize, *const *const u8) -> _`
+              found signature `fn() -> _`
+
+error: `miri_start` must have the following signature:
+       fn miri_start(argc: isize, argv: *const *const u8) -> isize
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.

src/tools/miri/test_dependencies/Cargo.lock

@@ -1,2 +1,2 @@
-//@error-in-other-file: miri can only run programs that have a main function
+//@error-in-other-file: Miri can only run programs that have a main function.
 #![no_main]

src/tools/miri/tests/fail-dep/tokio/sleep.stderr

@@ -1,4 +1,11 @@
-error: miri can only run programs that have a main function
+error: Miri can only run programs that have a main function.
+       Alternatively, you can export a `miri_start` function:
+       
+       #[cfg(miri)]
+       #[no_mangle]
+       fn miri_start(argc: isize, argv: *const *const u8) -> isize {
+           // Call the actual start function that your project implements, based on your target's conventions.
+       }
 
 error: aborting due to 1 previous error
 

src/tools/miri/tests/fail/miri_start_wrong_sig.rs

@@ -0,0 +1,70 @@
+//@ignore-target-windows: File handling is not implemented yet
+//@compile-flags: -Zmiri-disable-isolation
+
+use std::{fs::File, io::Error, os::fd::AsRawFd};
+
+#[path = "../../utils/mod.rs"]
+mod utils;
+
+fn main() {
+    let bytes = b"Hello, World!\n";
+    let path = utils::prepare_with_content("miri_test_fs_shared_lock.txt", bytes);
+
+    let files: Vec<File> = (0..3).map(|_| File::open(&path).unwrap()).collect();
+
+    // Test that we can apply many shared locks
+    for file in files.iter() {
+        let fd = file.as_raw_fd();
+        let ret = unsafe { libc::flock(fd, libc::LOCK_SH) };
+        if ret != 0 {
+            panic!("flock error: {}", Error::last_os_error());
+        }
+    }
+
+    // Test that shared lock prevents exclusive lock
+    {
+        let fd = files[0].as_raw_fd();
+        let ret = unsafe { libc::flock(fd, libc::LOCK_EX | libc::LOCK_NB) };
+        assert_eq!(ret, -1);
+        let err = Error::last_os_error().raw_os_error().unwrap();
+        assert_eq!(err, libc::EWOULDBLOCK);
+    }
+
+    // Unlock shared lock
+    for file in files.iter() {
+        let fd = file.as_raw_fd();
+        let ret = unsafe { libc::flock(fd, libc::LOCK_UN) };
+        if ret != 0 {
+            panic!("flock error: {}", Error::last_os_error());
+        }
+    }
+
+    // Take exclusive lock
+    {
+        let fd = files[0].as_raw_fd();
+        let ret = unsafe { libc::flock(fd, libc::LOCK_EX) };
+        assert_eq!(ret, 0);
+    }
+
+    // Test that shared lock prevents exclusive and shared locks
+    {
+        let fd = files[1].as_raw_fd();
+        let ret = unsafe { libc::flock(fd, libc::LOCK_EX | libc::LOCK_NB) };
+        assert_eq!(ret, -1);
+        let err = Error::last_os_error().raw_os_error().unwrap();
+        assert_eq!(err, libc::EWOULDBLOCK);
+
+        let fd = files[2].as_raw_fd();
+        let ret = unsafe { libc::flock(fd, libc::LOCK_SH | libc::LOCK_NB) };
+        assert_eq!(ret, -1);
+        let err = Error::last_os_error().raw_os_error().unwrap();
+        assert_eq!(err, libc::EWOULDBLOCK);
+    }
+
+    // Unlock exclusive lock
+    {
+        let fd = files[0].as_raw_fd();
+        let ret = unsafe { libc::flock(fd, libc::LOCK_UN) };
+        assert_eq!(ret, 0);
+    }
+}

src/tools/miri/tests/fail/miri_start_wrong_sig.stderr

@@ -0,0 +1,19 @@
+//@compile-flags: -Cpanic=abort
+#![no_main]
+#![no_std]
+
+use core::fmt::Write;
+
+#[path = "../utils/mod.no_std.rs"]
+mod utils;
+
+#[no_mangle]
+fn miri_start(_argc: isize, _argv: *const *const u8) -> isize {
+    writeln!(utils::MiriStdout, "Hello from miri_start!").unwrap();
+    0
+}
+
+#[panic_handler]
+fn panic_handler(_: &core::panic::PanicInfo) -> ! {
+    loop {}
+}

src/tools/miri/tests/fail/no_main.rs

@@ -0,0 +1 @@
+Hello from miri_start!

src/tools/miri/tests/fail/no_main.stderr

@@ -73,7 +73,7 @@ fn miri_config(target: &str, path: &str, mode: Mode, with_dependencies: bool) ->
         stdout_filters: stdout_filters().into(),
         mode,
         program,
-        out_dir: PathBuf::from(std::env::var_os("CARGO_TARGET_DIR").unwrap()).join("ui"),
+        out_dir: PathBuf::from(std::env::var_os("CARGO_TARGET_DIR").unwrap()).join("miri_ui"),
         edition: Some("2021".into()), // keep in sync with `./miri run`
         threads: std::env::var("MIRI_TEST_THREADS")
             .ok()