freebsd adding getentropy interception support

ci.sh

@@ -108,7 +108,7 @@ case $HOST_TARGET in
     MIRI_TEST_TARGET=aarch64-unknown-linux-gnu run_tests
     MIRI_TEST_TARGET=aarch64-apple-darwin run_tests
     MIRI_TEST_TARGET=i686-pc-windows-gnu run_tests
-    MIRI_TEST_TARGET=x86_64-unknown-freebsd run_tests_minimal hello integer vec panic/panic concurrency/simple pthreads atomic env/var
+    MIRI_TEST_TARGET=x86_64-unknown-freebsd run_tests_minimal hello integer vec panic/panic concurrency/simple pthreads libc-getentropy atomic env/var
     MIRI_TEST_TARGET=aarch64-linux-android run_tests_minimal hello integer vec panic/panic
     MIRI_TEST_TARGET=wasm32-wasi run_tests_minimal no_std integer strings wasm
     MIRI_TEST_TARGET=wasm32-unknown-unknown run_tests_minimal no_std integer strings wasm

src/shims/unix/freebsd/foreign_items.rs

@@ -47,6 +47,23 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                     this.read_scalar(len)?,
                 )?;
             }
+            "getentropy" => {
+                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.
+                // https://man.freebsd.org/cgi/man.cgi?query=getentropy&sektion=3&format=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)?;
+                }
+            }
 
             // errno
             "__error" => {

tests/pass-dep/shims/libc-getentropy.rs

@@ -0,0 +1,11 @@
+//@only-target-freebsd
+
+fn main() {
+    let mut buf1 = [0u8; 256];
+    let mut buf2 = [0u8; 257];
+    unsafe {
+        assert_eq!(libc::getentropy(buf1.as_mut_ptr() as *mut libc::c_void, buf1.len()), 0);
+        assert_eq!(libc::getentropy(buf2.as_mut_ptr() as *mut libc::c_void, buf2.len()), -1);
+        assert_eq!(std::io::Error::last_os_error().raw_os_error().unwrap(), libc::EIO);
+    }
+}