Auto merge of rust-lang#3098 - BlackHoleFox:apple-entropy, r=RalfJung

Support getentropy on macOS as a foreign item

Prior this was always assumed to be accessed via `dlsym` shim, but in `std` I'm attempting to start [unconditionally linking](rust-lang#116319) to `getentropy` on macOS now that Rust's platform version support allows it.

This just moves the main logic of the previous `dlsym` handler into an eval context extension so it can be used via both call paths. The `dlsym` handler is still needed as `getrandom` uses it.

src/tools/miri/src/shims/unix/macos/dlsym.rs

@@ -2,6 +2,7 @@ use rustc_middle::mir;
 
 use log::trace;
 
+use super::foreign_items::EvalContextExt as _;
 use crate::*;
 use helpers::check_arg_count;
 
@@ -38,10 +39,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         match dlsym {
             Dlsym::getentropy => {
                 let [ptr, len] = check_arg_count(args)?;
-                let ptr = this.read_pointer(ptr)?;
-                let len = this.read_target_usize(len)?;
-                this.gen_random(ptr, len)?;
-                this.write_null(dest)?;
+                let result = this.getentropy(ptr, len)?;
+                this.write_scalar(result, dest)?;
             }
         }
 

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

@@ -109,6 +109,14 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                 this.write_scalar(result, dest)?;
             }
 
+            // Random generation related shims
+            "getentropy" => {
+                let [buf, bufsize] =
+                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
+                let result = this.getentropy(buf, bufsize)?;
+                this.write_scalar(result, dest)?;
+            }
+
             // Access to command-line arguments
             "_NSGetArgc" => {
                 let [] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
@@ -198,4 +206,19 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
 
         Ok(EmulateByNameResult::NeedsJumping)
     }
+
+    fn getentropy(
+        &mut self,
+        buffer_op: &OpTy<'tcx, Provenance>,
+        length_op: &OpTy<'tcx, Provenance>,
+    ) -> InterpResult<'tcx, Scalar<Provenance>> {
+        let this = self.eval_context_mut();
+        this.assert_target_os("macos", "getentropy");
+
+        let ptr = this.read_pointer(buffer_op)?;
+        let len = this.read_target_usize(length_op)?;
+        this.gen_random(ptr, len)?;
+
+        Ok(Scalar::from_i32(0)) // KERN_SUCCESS
+    }
 }