Auto merge of #3564 - RalfJung:pthread-sync, r=RalfJung

pthread shims: reorganize field offset handling, and add sanity checks

6 files changed, 235 insertions, 195 deletions

diff --git a/src/tools/miri/src/helpers.rs b/src/tools/miri/src/helpers.rs
index f81e997efd8..40c2008ac94 100644
--- a/src/tools/miri/src/helpers.rs
+++ b/src/tools/miri/src/helpers.rs
@@ -255,14 +255,19 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     }
 
     /// Evaluates the scalar at the specified path.
-    fn eval_path_scalar(&self, path: &[&str]) -> Scalar<Provenance> {
+    fn eval_path(&self, path: &[&str]) -> OpTy<'tcx, Provenance> {
         let this = self.eval_context_ref();
         let instance = this.resolve_path(path, Namespace::ValueNS);
         // We don't give a span -- this isn't actually used directly by the program anyway.
         let const_val = this.eval_global(instance).unwrap_or_else(|err| {
             panic!("failed to evaluate required Rust item: {path:?}\n{err:?}")
         });
-        this.read_scalar(&const_val)
+        const_val.into()
+    }
+    fn eval_path_scalar(&self, path: &[&str]) -> Scalar<Provenance> {
+        let this = self.eval_context_ref();
+        let val = this.eval_path(path);
+        this.read_scalar(&val)
             .unwrap_or_else(|err| panic!("failed to read required Rust item: {path:?}\n{err:?}"))
     }
 
diff --git a/src/tools/miri/src/shims/unix/foreign_items.rs b/src/tools/miri/src/shims/unix/foreign_items.rs
index 3d3a510c4a2..45793602b21 100644
--- a/src/tools/miri/src/shims/unix/foreign_items.rs
+++ b/src/tools/miri/src/shims/unix/foreign_items.rs
@@ -490,6 +490,18 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                 let result = this.pthread_condattr_init(attr)?;
                 this.write_scalar(Scalar::from_i32(result), dest)?;
             }
+            "pthread_condattr_setclock" => {
+                let [attr, clock_id] =
+                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
+                let result = this.pthread_condattr_setclock(attr, clock_id)?;
+                this.write_scalar(result, dest)?;
+            }
+            "pthread_condattr_getclock" => {
+                let [attr, clock_id] =
+                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
+                let result = this.pthread_condattr_getclock(attr, clock_id)?;
+                this.write_scalar(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)?;
diff --git a/src/tools/miri/src/shims/unix/linux/foreign_items.rs b/src/tools/miri/src/shims/unix/linux/foreign_items.rs
index 9b3302359ae..43b5db9e32d 100644
--- a/src/tools/miri/src/shims/unix/linux/foreign_items.rs
+++ b/src/tools/miri/src/shims/unix/linux/foreign_items.rs
@@ -73,18 +73,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
             }
 
             // Threading
-            "pthread_condattr_setclock" => {
-                let [attr, clock_id] =
-                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
-                let result = this.pthread_condattr_setclock(attr, clock_id)?;
-                this.write_scalar(result, dest)?;
-            }
-            "pthread_condattr_getclock" => {
-                let [attr, clock_id] =
-                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
-                let result = this.pthread_condattr_getclock(attr, clock_id)?;
-                this.write_scalar(result, dest)?;
-            }
             "pthread_setname_np" => {
                 let [thread, name] =
                     this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
diff --git a/src/tools/miri/src/shims/unix/solarish/foreign_items.rs b/src/tools/miri/src/shims/unix/solarish/foreign_items.rs
index 5bf4a7621d0..16a04727561 100644
--- a/src/tools/miri/src/shims/unix/solarish/foreign_items.rs
+++ b/src/tools/miri/src/shims/unix/solarish/foreign_items.rs
@@ -1,7 +1,6 @@
 use rustc_span::Symbol;
 use rustc_target::spec::abi::Abi;
 
-use crate::shims::unix::*;
 use crate::*;
 use shims::EmulateItemResult;
 
@@ -11,6 +10,7 @@ pub fn is_dyn_sym(_name: &str) -> bool {
 
 impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriInterpCx<'mir, 'tcx> {}
 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
+    #[allow(warnings)]
     fn emulate_foreign_item_inner(
         &mut self,
         link_name: Symbol,
@@ -20,20 +20,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     ) -> InterpResult<'tcx, EmulateItemResult> {
         let this = self.eval_context_mut();
         match link_name.as_str() {
-            // Threading
-            "pthread_condattr_setclock" => {
-                let [attr, clock_id] =
-                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
-                let result = this.pthread_condattr_setclock(attr, clock_id)?;
-                this.write_scalar(result, dest)?;
-            }
-            "pthread_condattr_getclock" => {
-                let [attr, clock_id] =
-                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
-                let result = this.pthread_condattr_getclock(attr, clock_id)?;
-                this.write_scalar(result, dest)?;
-            }
-
             _ => return Ok(EmulateItemResult::NotSupported),
         }
         Ok(EmulateItemResult::NeedsJumping)
diff --git a/src/tools/miri/src/shims/unix/sync.rs b/src/tools/miri/src/shims/unix/sync.rs
index 2c9208deb3c..f24f279ab0f 100644
--- a/src/tools/miri/src/shims/unix/sync.rs
+++ b/src/tools/miri/src/shims/unix/sync.rs
@@ -1,34 +1,23 @@
+use std::sync::atomic::{AtomicBool, Ordering};
 use std::time::SystemTime;
 
+use rustc_target::abi::Size;
+
 use crate::concurrency::thread::MachineCallback;
 use crate::*;
 
 // pthread_mutexattr_t is either 4 or 8 bytes, depending on the platform.
+// We ignore the platform layout and store our own fields:
+// - kind: i32
 
-// Our chosen memory layout for emulation (does not have to match the platform layout!):
-// store an i32 in the first four bytes equal to the corresponding libc mutex kind constant
-// (e.g. PTHREAD_MUTEX_NORMAL).
-
-/// A flag that allows to distinguish `PTHREAD_MUTEX_NORMAL` from
-/// `PTHREAD_MUTEX_DEFAULT`. Since in `glibc` they have the same numeric values,
-/// but different behaviour, we need a way to distinguish them. We do this by
-/// setting this bit flag to the `PTHREAD_MUTEX_NORMAL` mutexes. See the comment
-/// in `pthread_mutexattr_settype` function.
-const PTHREAD_MUTEX_NORMAL_FLAG: i32 = 0x8000000;
-
-fn is_mutex_kind_default<'mir, 'tcx: 'mir>(
-    ecx: &MiriInterpCx<'mir, 'tcx>,
-    kind: i32,
-) -> InterpResult<'tcx, bool> {
-    Ok(kind == ecx.eval_libc_i32("PTHREAD_MUTEX_DEFAULT"))
-}
-
-fn is_mutex_kind_normal<'mir, 'tcx: 'mir>(
+#[inline]
+fn mutexattr_kind_offset<'mir, 'tcx: 'mir>(
     ecx: &MiriInterpCx<'mir, 'tcx>,
-    kind: i32,
-) -> InterpResult<'tcx, bool> {
-    let mutex_normal_kind = ecx.eval_libc_i32("PTHREAD_MUTEX_NORMAL");
-    Ok(kind == (mutex_normal_kind | PTHREAD_MUTEX_NORMAL_FLAG))
+) -> InterpResult<'tcx, u64> {
+    Ok(match &*ecx.tcx.sess.target.os {
+        "linux" | "illumos" | "solaris" | "macos" => 0,
+        os => throw_unsup_format!("`pthread_mutexattr` is not supported on {os}"),
+    })
 }
 
 fn mutexattr_get_kind<'mir, 'tcx: 'mir>(
@@ -37,7 +26,7 @@ fn mutexattr_get_kind<'mir, 'tcx: 'mir>(
 ) -> InterpResult<'tcx, i32> {
     ecx.deref_pointer_and_read(
         attr_op,
-        0,
+        mutexattr_kind_offset(ecx)?,
         ecx.libc_ty_layout("pthread_mutexattr_t"),
         ecx.machine.layouts.i32,
     )?
@@ -51,26 +40,88 @@ fn mutexattr_set_kind<'mir, 'tcx: 'mir>(
 ) -> InterpResult<'tcx, ()> {
     ecx.deref_pointer_and_write(
         attr_op,
-        0,
+        mutexattr_kind_offset(ecx)?,
         Scalar::from_i32(kind),
         ecx.libc_ty_layout("pthread_mutexattr_t"),
         ecx.machine.layouts.i32,
     )
 }
 
+/// A flag that allows to distinguish `PTHREAD_MUTEX_NORMAL` from
+/// `PTHREAD_MUTEX_DEFAULT`. Since in `glibc` they have the same numeric values,
+/// but different behaviour, we need a way to distinguish them. We do this by
+/// setting this bit flag to the `PTHREAD_MUTEX_NORMAL` mutexes. See the comment
+/// in `pthread_mutexattr_settype` function.
+const PTHREAD_MUTEX_NORMAL_FLAG: i32 = 0x8000000;
+
+fn is_mutex_kind_default<'mir, 'tcx: 'mir>(
+    ecx: &MiriInterpCx<'mir, 'tcx>,
+    kind: i32,
+) -> InterpResult<'tcx, bool> {
+    Ok(kind == ecx.eval_libc_i32("PTHREAD_MUTEX_DEFAULT"))
+}
+
+fn is_mutex_kind_normal<'mir, 'tcx: 'mir>(
+    ecx: &MiriInterpCx<'mir, 'tcx>,
+    kind: i32,
+) -> InterpResult<'tcx, bool> {
+    let mutex_normal_kind = ecx.eval_libc_i32("PTHREAD_MUTEX_NORMAL");
+    Ok(kind == (mutex_normal_kind | PTHREAD_MUTEX_NORMAL_FLAG))
+}
+
 // pthread_mutex_t is between 24 and 48 bytes, depending on the platform.
+// We ignore the platform layout and store our own fields:
+// - id: u32
+// - kind: i32
+
+fn mutex_id_offset<'mir, 'tcx: 'mir>(ecx: &MiriInterpCx<'mir, 'tcx>) -> InterpResult<'tcx, u64> {
+    let offset = match &*ecx.tcx.sess.target.os {
+        "linux" | "illumos" | "solaris" => 0,
+        // macOS stores a signature in the first bytes, so we have to move to offset 4.
+        "macos" => 4,
+        os => throw_unsup_format!("`pthread_mutex` is not supported on {os}"),
+    };
+
+    // Sanity-check this against PTHREAD_MUTEX_INITIALIZER (but only once):
+    // the id must start out as 0.
+    static SANITY: AtomicBool = AtomicBool::new(false);
+    if !SANITY.swap(true, Ordering::Relaxed) {
+        let static_initializer = ecx.eval_path(&["libc", "PTHREAD_MUTEX_INITIALIZER"]);
+        let id_field = static_initializer
+            .offset(Size::from_bytes(offset), ecx.machine.layouts.u32, ecx)
+            .unwrap();
+        let id = ecx.read_scalar(&id_field).unwrap().to_u32().unwrap();
+        assert_eq!(
+            id, 0,
+            "PTHREAD_MUTEX_INITIALIZER is incompatible with our pthread_mutex layout: id is not 0"
+        );
+    }
 
-// Our chosen memory layout for the emulated mutex (does not have to match the platform layout!):
-// bytes 0-3: reserved for signature on macOS
-// (need to avoid this because it is set by static initializer macros)
-// bytes 4-7: mutex id as u32 or 0 if id is not assigned yet.
-// bytes 12-15 or 16-19 (depending on platform): mutex kind, as an i32
-// (the kind has to be at this particular offset for compatibility with Linux's static initializer
-// macros, e.g. PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP.)
+    Ok(offset)
+}
 
-#[inline]
-fn mutex_id_offset<'mir, 'tcx: 'mir>(ecx: &MiriInterpCx<'mir, 'tcx>) -> u64 {
-    if matches!(&*ecx.tcx.sess.target.os, "macos") { 4 } else { 0 }
+fn mutex_kind_offset<'mir, 'tcx: 'mir>(ecx: &MiriInterpCx<'mir, 'tcx>) -> u64 {
+    // These offsets are picked for compatibility with Linux's static initializer
+    // macros, e.g. PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP.)
+    let offset = if ecx.pointer_size().bytes() == 8 { 16 } else { 12 };
+
+    // Sanity-check this against PTHREAD_MUTEX_INITIALIZER (but only once):
+    // the kind must start out as PTHREAD_MUTEX_DEFAULT.
+    static SANITY: AtomicBool = AtomicBool::new(false);
+    if !SANITY.swap(true, Ordering::Relaxed) {
+        let static_initializer = ecx.eval_path(&["libc", "PTHREAD_MUTEX_INITIALIZER"]);
+        let kind_field = static_initializer
+            .offset(Size::from_bytes(mutex_kind_offset(ecx)), ecx.machine.layouts.i32, ecx)
+            .unwrap();
+        let kind = ecx.read_scalar(&kind_field).unwrap().to_i32().unwrap();
+        assert_eq!(
+            kind,
+            ecx.eval_libc_i32("PTHREAD_MUTEX_DEFAULT"),
+            "PTHREAD_MUTEX_INITIALIZER is incompatible with our pthread_mutex layout: kind is not PTHREAD_MUTEX_DEFAULT"
+        );
+    }
+
+    offset
 }
 
 fn mutex_get_id<'mir, 'tcx: 'mir>(
@@ -80,7 +131,7 @@ fn mutex_get_id<'mir, 'tcx: 'mir>(
     ecx.mutex_get_or_create_id(
         mutex_op,
         ecx.libc_ty_layout("pthread_mutex_t"),
-        mutex_id_offset(ecx),
+        mutex_id_offset(ecx)?,
     )
 }
 
@@ -90,8 +141,8 @@ fn mutex_reset_id<'mir, 'tcx: 'mir>(
 ) -> InterpResult<'tcx, ()> {
     ecx.deref_pointer_and_write(
         mutex_op,
-        mutex_id_offset(ecx),
-        Scalar::from_i32(0),
+        mutex_id_offset(ecx)?,
+        Scalar::from_u32(0),
         ecx.libc_ty_layout("pthread_mutex_t"),
         ecx.machine.layouts.u32,
     )
@@ -101,10 +152,9 @@ fn mutex_get_kind<'mir, 'tcx: 'mir>(
     ecx: &MiriInterpCx<'mir, 'tcx>,
     mutex_op: &OpTy<'tcx, Provenance>,
 ) -> InterpResult<'tcx, i32> {
-    let offset = if ecx.pointer_size().bytes() == 8 { 16 } else { 12 };
     ecx.deref_pointer_and_read(
         mutex_op,
-        offset,
+        mutex_kind_offset(ecx),
         ecx.libc_ty_layout("pthread_mutex_t"),
         ecx.machine.layouts.i32,
     )?
@@ -116,10 +166,9 @@ fn mutex_set_kind<'mir, 'tcx: 'mir>(
     mutex_op: &OpTy<'tcx, Provenance>,
     kind: i32,
 ) -> InterpResult<'tcx, ()> {
-    let offset = if ecx.pointer_size().bytes() == 8 { 16 } else { 12 };
     ecx.deref_pointer_and_write(
         mutex_op,
-        offset,
+        mutex_kind_offset(ecx),
         Scalar::from_i32(kind),
         ecx.libc_ty_layout("pthread_mutex_t"),
         ecx.machine.layouts.i32,
@@ -127,15 +176,33 @@ fn mutex_set_kind<'mir, 'tcx: 'mir>(
 }
 
 // pthread_rwlock_t is between 32 and 56 bytes, depending on the platform.
+// We ignore the platform layout and store our own fields:
+// - id: u32
+
+fn rwlock_id_offset<'mir, 'tcx: 'mir>(ecx: &MiriInterpCx<'mir, 'tcx>) -> InterpResult<'tcx, u64> {
+    let offset = match &*ecx.tcx.sess.target.os {
+        "linux" | "illumos" | "solaris" => 0,
+        // macOS stores a signature in the first bytes, so we have to move to offset 4.
+        "macos" => 4,
+        os => throw_unsup_format!("`pthread_rwlock` is not supported on {os}"),
+    };
+
+    // Sanity-check this against PTHREAD_RWLOCK_INITIALIZER (but only once):
+    // the id must start out as 0.
+    static SANITY: AtomicBool = AtomicBool::new(false);
+    if !SANITY.swap(true, Ordering::Relaxed) {
+        let static_initializer = ecx.eval_path(&["libc", "PTHREAD_RWLOCK_INITIALIZER"]);
+        let id_field = static_initializer
+            .offset(Size::from_bytes(offset), ecx.machine.layouts.u32, ecx)
+            .unwrap();
+        let id = ecx.read_scalar(&id_field).unwrap().to_u32().unwrap();
+        assert_eq!(
+            id, 0,
+            "PTHREAD_RWLOCK_INITIALIZER is incompatible with our pthread_rwlock layout: id is not 0"
+        );
+    }
 
-// Our chosen memory layout for the emulated rwlock (does not have to match the platform layout!):
-// bytes 0-3: reserved for signature on macOS
-// (need to avoid this because it is set by static initializer macros)
-// bytes 4-7: rwlock id as u32 or 0 if id is not assigned yet.
-
-#[inline]
-fn rwlock_id_offset<'mir, 'tcx: 'mir>(ecx: &MiriInterpCx<'mir, 'tcx>) -> u64 {
-    if matches!(&*ecx.tcx.sess.target.os, "macos") { 4 } else { 0 }
+    Ok(offset)
 }
 
 fn rwlock_get_id<'mir, 'tcx: 'mir>(
@@ -145,17 +212,24 @@ fn rwlock_get_id<'mir, 'tcx: 'mir>(
     ecx.rwlock_get_or_create_id(
         rwlock_op,
         ecx.libc_ty_layout("pthread_rwlock_t"),
-        rwlock_id_offset(ecx),
+        rwlock_id_offset(ecx)?,
     )
 }
 
-// pthread_condattr_t
-
-// Our chosen memory layout for emulation (does not have to match the platform layout!):
-// store an i32 in the first four bytes equal to the corresponding libc clock id constant
-// (e.g. CLOCK_REALTIME).
+// pthread_condattr_t.
+// We ignore the platform layout and store our own fields:
+// - clock: i32
 
-const CONDATTR_CLOCK_OFFSET: u64 = 0;
+#[inline]
+fn condattr_clock_offset<'mir, 'tcx: 'mir>(
+    ecx: &MiriInterpCx<'mir, 'tcx>,
+) -> InterpResult<'tcx, u64> {
+    Ok(match &*ecx.tcx.sess.target.os {
+        "linux" | "illumos" | "solaris" => 0,
+        // macOS does not have a clock attribute.
+        os => throw_unsup_format!("`pthread_condattr` clock field is not supported on {os}"),
+    })
+}
 
 fn condattr_get_clock_id<'mir, 'tcx: 'mir>(
     ecx: &MiriInterpCx<'mir, 'tcx>,
@@ -163,7 +237,7 @@ fn condattr_get_clock_id<'mir, 'tcx: 'mir>(
 ) -> InterpResult<'tcx, i32> {
     ecx.deref_pointer_and_read(
         attr_op,
-        CONDATTR_CLOCK_OFFSET,
+        condattr_clock_offset(ecx)?,
         ecx.libc_ty_layout("pthread_condattr_t"),
         ecx.machine.layouts.i32,
     )?
@@ -177,34 +251,86 @@ fn condattr_set_clock_id<'mir, 'tcx: 'mir>(
 ) -> InterpResult<'tcx, ()> {
     ecx.deref_pointer_and_write(
         attr_op,
-        CONDATTR_CLOCK_OFFSET,
+        condattr_clock_offset(ecx)?,
         Scalar::from_i32(clock_id),
         ecx.libc_ty_layout("pthread_condattr_t"),
         ecx.machine.layouts.i32,
     )
 }
 
-// pthread_cond_t
+// pthread_cond_t.
+// We ignore the platform layout and store our own fields:
+// - id: u32
+// - clock: i32
+
+fn cond_id_offset<'mir, 'tcx: 'mir>(ecx: &MiriInterpCx<'mir, 'tcx>) -> InterpResult<'tcx, u64> {
+    let offset = match &*ecx.tcx.sess.target.os {
+        "linux" | "illumos" | "solaris" => 0,
+        // macOS stores a signature in the first bytes, so we have to move to offset 4.
+        "macos" => 4,
+        os => throw_unsup_format!("`pthread_cond` is not supported on {os}"),
+    };
+
+    // Sanity-check this against PTHREAD_COND_INITIALIZER (but only once):
+    // the id must start out as 0.
+    static SANITY: AtomicBool = AtomicBool::new(false);
+    if !SANITY.swap(true, Ordering::Relaxed) {
+        let static_initializer = ecx.eval_path(&["libc", "PTHREAD_COND_INITIALIZER"]);
+        let id_field = static_initializer
+            .offset(Size::from_bytes(offset), ecx.machine.layouts.u32, ecx)
+            .unwrap();
+        let id = ecx.read_scalar(&id_field).unwrap().to_u32().unwrap();
+        assert_eq!(
+            id, 0,
+            "PTHREAD_COND_INITIALIZER is incompatible with our pthread_cond layout: id is not 0"
+        );
+    }
 
-// Our chosen memory layout for the emulated conditional variable (does not have
-// to match the platform layout!):
+    Ok(offset)
+}
 
-// bytes 0-3: reserved for signature on macOS
-// bytes 4-7: the conditional variable id as u32 or 0 if id is not assigned yet.
-// bytes 8-11: the clock id constant as i32
+/// Determines whether this clock represents the real-time clock, CLOCK_REALTIME.
+fn is_cond_clock_realtime<'mir, 'tcx: 'mir>(ecx: &MiriInterpCx<'mir, 'tcx>, clock_id: i32) -> bool {
+    // To ensure compatibility with PTHREAD_COND_INITIALIZER on all platforms,
+    // we can't just compare with CLOCK_REALTIME: on Solarish, PTHREAD_COND_INITIALIZER
+    // makes the clock 0 but CLOCK_REALTIME is 3.
+    // However, we need to always be able to distinguish this from CLOCK_MONOTONIC.
+    clock_id == ecx.eval_libc_i32("CLOCK_REALTIME")
+        || (clock_id == 0 && clock_id != ecx.eval_libc_i32("CLOCK_MONOTONIC"))
+}
 
-const CONDVAR_CLOCK_OFFSET: u64 = 8;
+fn cond_clock_offset<'mir, 'tcx: 'mir>(ecx: &MiriInterpCx<'mir, 'tcx>) -> u64 {
+    // macOS doesn't have a clock attribute, but to keep the code uniform we store
+    // a clock ID in the pthread_cond_t anyway. There's enough space.
+    let offset = 8;
+
+    // Sanity-check this against PTHREAD_COND_INITIALIZER (but only once):
+    // the clock must start out as CLOCK_REALTIME.
+    static SANITY: AtomicBool = AtomicBool::new(false);
+    if !SANITY.swap(true, Ordering::Relaxed) {
+        let static_initializer = ecx.eval_path(&["libc", "PTHREAD_COND_INITIALIZER"]);
+        let id_field = static_initializer
+            .offset(Size::from_bytes(offset), ecx.machine.layouts.i32, ecx)
+            .unwrap();
+        let id = ecx.read_scalar(&id_field).unwrap().to_i32().unwrap();
+        assert!(
+            is_cond_clock_realtime(ecx, id),
+            "PTHREAD_COND_INITIALIZER is incompatible with our pthread_cond layout: clock is not CLOCK_REALTIME"
+        );
+    }
 
-#[inline]
-fn cond_id_offset<'mir, 'tcx: 'mir>(ecx: &MiriInterpCx<'mir, 'tcx>) -> u64 {
-    if matches!(&*ecx.tcx.sess.target.os, "macos") { 4 } else { 0 }
+    offset
 }
 
 fn cond_get_id<'mir, 'tcx: 'mir>(
     ecx: &mut MiriInterpCx<'mir, 'tcx>,
     cond_op: &OpTy<'tcx, Provenance>,
 ) -> InterpResult<'tcx, CondvarId> {
-    ecx.condvar_get_or_create_id(cond_op, ecx.libc_ty_layout("pthread_cond_t"), cond_id_offset(ecx))
+    ecx.condvar_get_or_create_id(
+        cond_op,
+        ecx.libc_ty_layout("pthread_cond_t"),
+        cond_id_offset(ecx)?,
+    )
 }
 
 fn cond_reset_id<'mir, 'tcx: 'mir>(
@@ -213,7 +339,7 @@ fn cond_reset_id<'mir, 'tcx: 'mir>(
 ) -> InterpResult<'tcx, ()> {
     ecx.deref_pointer_and_write(
         cond_op,
-        cond_id_offset(ecx),
+        cond_id_offset(ecx)?,
         Scalar::from_i32(0),
         ecx.libc_ty_layout("pthread_cond_t"),
         ecx.machine.layouts.u32,
@@ -226,7 +352,7 @@ fn cond_get_clock_id<'mir, 'tcx: 'mir>(
 ) -> InterpResult<'tcx, i32> {
     ecx.deref_pointer_and_read(
         cond_op,
-        CONDVAR_CLOCK_OFFSET,
+        cond_clock_offset(ecx),
         ecx.libc_ty_layout("pthread_cond_t"),
         ecx.machine.layouts.i32,
     )?
@@ -240,7 +366,7 @@ fn cond_set_clock_id<'mir, 'tcx: 'mir>(
 ) -> InterpResult<'tcx, ()> {
     ecx.deref_pointer_and_write(
         cond_op,
-        CONDVAR_CLOCK_OFFSET,
+        cond_clock_offset(ecx),
         Scalar::from_i32(clock_id),
         ecx.libc_ty_layout("pthread_cond_t"),
         ecx.machine.layouts.i32,
@@ -307,13 +433,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     ) -> InterpResult<'tcx, i32> {
         let this = self.eval_context_mut();
 
-        if !matches!(&*this.tcx.sess.target.os, "linux" | "macos" | "solaris" | "illumos") {
-            throw_unsup_format!(
-                "`pthread_mutexattr_init` is not supported on {}",
-                this.tcx.sess.target.os
-            );
-        }
-
         let default_kind = this.eval_libc_i32("PTHREAD_MUTEX_DEFAULT");
         mutexattr_set_kind(this, attr_op, default_kind)?;
 
@@ -396,13 +515,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     ) -> InterpResult<'tcx, i32> {
         let this = self.eval_context_mut();
 
-        if !matches!(&*this.tcx.sess.target.os, "linux" | "macos" | "solaris" | "illumos") {
-            throw_unsup_format!(
-                "`pthread_mutex_init` is not supported on {}",
-                this.tcx.sess.target.os
-            );
-        }
-
         let attr = this.read_pointer(attr_op)?;
         let kind = if this.ptr_is_null(attr)? {
             this.eval_libc_i32("PTHREAD_MUTEX_DEFAULT")
@@ -557,13 +669,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     ) -> InterpResult<'tcx, i32> {
         let this = self.eval_context_mut();
 
-        if !matches!(&*this.tcx.sess.target.os, "linux" | "macos" | "solaris" | "illumos") {
-            throw_unsup_format!(
-                "`pthread_rwlock_rdlock` is not supported on {}",
-                this.tcx.sess.target.os
-            );
-        }
-
         let id = rwlock_get_id(this, rwlock_op)?;
         let active_thread = this.get_active_thread();
 
@@ -582,13 +687,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     ) -> InterpResult<'tcx, i32> {
         let this = self.eval_context_mut();
 
-        if !matches!(&*this.tcx.sess.target.os, "linux" | "macos" | "solaris" | "illumos") {
-            throw_unsup_format!(
-                "`pthread_rwlock_tryrdlock` is not supported on {}",
-                this.tcx.sess.target.os
-            );
-        }
-
         let id = rwlock_get_id(this, rwlock_op)?;
         let active_thread = this.get_active_thread();
 
@@ -606,13 +704,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     ) -> InterpResult<'tcx, i32> {
         let this = self.eval_context_mut();
 
-        if !matches!(&*this.tcx.sess.target.os, "linux" | "macos" | "solaris" | "illumos") {
-            throw_unsup_format!(
-                "`pthread_rwlock_wrlock` is not supported on {}",
-                this.tcx.sess.target.os
-            );
-        }
-
         let id = rwlock_get_id(this, rwlock_op)?;
         let active_thread = this.get_active_thread();
 
@@ -643,13 +734,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     ) -> InterpResult<'tcx, i32> {
         let this = self.eval_context_mut();
 
-        if !matches!(&*this.tcx.sess.target.os, "linux" | "macos" | "solaris" | "illumos") {
-            throw_unsup_format!(
-                "`pthread_rwlock_trywrlock` is not supported on {}",
-                this.tcx.sess.target.os
-            );
-        }
-
         let id = rwlock_get_id(this, rwlock_op)?;
         let active_thread = this.get_active_thread();
 
@@ -667,13 +751,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     ) -> InterpResult<'tcx, i32> {
         let this = self.eval_context_mut();
 
-        if !matches!(&*this.tcx.sess.target.os, "linux" | "macos" | "solaris" | "illumos") {
-            throw_unsup_format!(
-                "`pthread_rwlock_unlock` is not supported on {}",
-                this.tcx.sess.target.os
-            );
-        }
-
         let id = rwlock_get_id(this, rwlock_op)?;
         let active_thread = this.get_active_thread();
 
@@ -693,13 +770,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     ) -> InterpResult<'tcx, i32> {
         let this = self.eval_context_mut();
 
-        if !matches!(&*this.tcx.sess.target.os, "linux" | "macos" | "solaris" | "illumos") {
-            throw_unsup_format!(
-                "`pthread_rwlock_destroy` is not supported on {}",
-                this.tcx.sess.target.os
-            );
-        }
-
         let id = rwlock_get_id(this, rwlock_op)?;
 
         if this.rwlock_is_locked(id) {
@@ -724,19 +794,15 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     ) -> InterpResult<'tcx, i32> {
         let this = self.eval_context_mut();
 
-        if !matches!(&*this.tcx.sess.target.os, "linux" | "macos" | "solaris" | "illumos") {
-            throw_unsup_format!(
-                "`pthread_condattr_init` is not supported on {}",
-                this.tcx.sess.target.os
-            );
+        // no clock attribute on macOS
+        if this.tcx.sess.target.os != "macos" {
+            // The default value of the clock attribute shall refer to the system
+            // clock.
+            // https://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_condattr_setclock.html
+            let default_clock_id = this.eval_libc_i32("CLOCK_REALTIME");
+            condattr_set_clock_id(this, attr_op, default_clock_id)?;
         }
 
-        // The default value of the clock attribute shall refer to the system
-        // clock.
-        // https://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_condattr_setclock.html
-        let default_clock_id = this.eval_libc_i32("CLOCK_REALTIME");
-        condattr_set_clock_id(this, attr_op, default_clock_id)?;
-
         Ok(0)
     }
 
@@ -747,14 +813,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     ) -> InterpResult<'tcx, Scalar<Provenance>> {
         let this = self.eval_context_mut();
 
-        // Does not exist on macOS!
-        if !matches!(&*this.tcx.sess.target.os, "linux" | "solaris" | "illumos") {
-            throw_unsup_format!(
-                "`pthread_condattr_setclock` is not supported on {}",
-                this.tcx.sess.target.os
-            );
-        }
-
         let clock_id = this.read_scalar(clock_id_op)?.to_i32()?;
         if clock_id == this.eval_libc_i32("CLOCK_REALTIME")
             || clock_id == this.eval_libc_i32("CLOCK_MONOTONIC")
@@ -775,14 +833,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     ) -> InterpResult<'tcx, Scalar<Provenance>> {
         let this = self.eval_context_mut();
 
-        // Does not exist on macOS!
-        if !matches!(&*this.tcx.sess.target.os, "linux" | "solaris" | "illumos") {
-            throw_unsup_format!(
-                "`pthread_condattr_getclock` is not supported on {}",
-                this.tcx.sess.target.os
-            );
-        }
-
         let clock_id = condattr_get_clock_id(this, attr_op)?;
         this.write_scalar(Scalar::from_i32(clock_id), &this.deref_pointer(clk_id_op)?)?;
 
@@ -796,8 +846,12 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         let this = self.eval_context_mut();
 
         // Destroying an uninit pthread_condattr is UB, so check to make sure it's not uninit.
-        condattr_get_clock_id(this, attr_op)?;
+        // There's no clock attribute on macOS.
+        if this.tcx.sess.target.os != "macos" {
+            condattr_get_clock_id(this, attr_op)?;
+        }
 
+        // De-init the entire thing.
         // This might lead to false positives, see comment in pthread_mutexattr_destroy
         this.write_uninit(
             &this.deref_pointer_as(attr_op, this.libc_ty_layout("pthread_condattr_t"))?,
@@ -813,15 +867,9 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     ) -> InterpResult<'tcx, i32> {
         let this = self.eval_context_mut();
 
-        if !matches!(&*this.tcx.sess.target.os, "linux" | "macos" | "solaris" | "illumos") {
-            throw_unsup_format!(
-                "`pthread_cond_init` is not supported on {}",
-                this.tcx.sess.target.os
-            );
-        }
-
         let attr = this.read_pointer(attr_op)?;
-        let clock_id = if this.ptr_is_null(attr)? {
+        // Default clock if `attr` is null, and on macOS where there is no clock attribute.
+        let clock_id = if this.ptr_is_null(attr)? || this.tcx.sess.target.os == "macos" {
             this.eval_libc_i32("CLOCK_REALTIME")
         } else {
             condattr_get_clock_id(this, attr_op)?
@@ -902,7 +950,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
             }
         };
 
-        let timeout_time = if clock_id == this.eval_libc_i32("CLOCK_REALTIME") {
+        let timeout_time = if is_cond_clock_realtime(this, clock_id) {
             this.check_no_isolation("`pthread_cond_timedwait` with `CLOCK_REALTIME`")?;
             CallbackTime::RealTime(SystemTime::UNIX_EPOCH.checked_add(duration).unwrap())
         } else if clock_id == this.eval_libc_i32("CLOCK_MONOTONIC") {
diff --git a/src/tools/miri/tests/fail-dep/shims/sync/libc_pthread_condattr_double_destroy.rs b/src/tools/miri/tests/fail-dep/shims/sync/libc_pthread_condattr_double_destroy.rs
index 13e639a867d..b5427d55eb0 100644
--- a/src/tools/miri/tests/fail-dep/shims/sync/libc_pthread_condattr_double_destroy.rs
+++ b/src/tools/miri/tests/fail-dep/shims/sync/libc_pthread_condattr_double_destroy.rs
@@ -1,4 +1,5 @@
 //@ignore-target-windows: No libc on Windows
+//@ignore-target-apple: Our macOS condattr don't have any fields so we do not notice this.
 
 /// Test that destroying a pthread_condattr twice fails, even without a check for number validity