diff --git a/src/tools/miri/tests/fail/alloc/alloc_error_handler_custom.rs b/src/tools/miri/tests/fail/alloc/alloc_error_handler_custom.rs
index 9f8837a626f4..babdb73f093a 100644
--- a/src/tools/miri/tests/fail/alloc/alloc_error_handler_custom.rs
+++ b/src/tools/miri/tests/fail/alloc/alloc_error_handler_custom.rs
@@ -7,15 +7,14 @@
 extern crate alloc;
 
 use alloc::alloc::*;
+use core::fmt::Write;
 
-extern "Rust" {
-    fn miri_write_to_stderr(bytes: &[u8]);
-}
+#[path = "../../utils/mod.no_std.rs"]
+mod utils;
 
 #[alloc_error_handler]
-fn alloc_error_handler(_: Layout) -> ! {
-    let msg = "custom alloc error handler called!\n";
-    unsafe { miri_write_to_stderr(msg.as_bytes()) };
+fn alloc_error_handler(layout: Layout) -> ! {
+    let _ = writeln!(utils::MiriStderr, "custom alloc error handler: {layout:?}");
     core::intrinsics::abort(); //~ERROR: aborted
 }
 
@@ -25,9 +24,7 @@ mod plumbing {
 
     #[panic_handler]
     fn panic_handler(_: &core::panic::PanicInfo) -> ! {
-        let msg = "custom panic handler called!\n";
-        unsafe { miri_write_to_stderr(msg.as_bytes()) };
-        core::intrinsics::abort();
+        loop {}
     }
 
     struct NoAlloc;
diff --git a/src/tools/miri/tests/fail/alloc/alloc_error_handler_custom.stderr b/src/tools/miri/tests/fail/alloc/alloc_error_handler_custom.stderr
index cdd666e5e0a5..5d9c2e2fb4c3 100644
--- a/src/tools/miri/tests/fail/alloc/alloc_error_handler_custom.stderr
+++ b/src/tools/miri/tests/fail/alloc/alloc_error_handler_custom.stderr
@@ -1,4 +1,4 @@
-custom alloc error handler called!
+custom alloc error handler: Layout { size: 4, align: 4 (1 << 2) }
 error: abnormal termination: the program aborted execution
   --> $DIR/alloc_error_handler_custom.rs:LL:CC
    |
@@ -12,8 +12,8 @@ note: inside `_::__rg_oom`
    |
 LL | #[alloc_error_handler]
    | ---------------------- in this procedural macro expansion
-LL | fn alloc_error_handler(_: Layout) -> ! {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL | fn alloc_error_handler(layout: Layout) -> ! {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: inside `alloc::alloc::handle_alloc_error::rt_error` at RUSTLIB/alloc/src/alloc.rs:LL:CC
    = note: inside `alloc::alloc::handle_alloc_error` at RUSTLIB/alloc/src/alloc.rs:LL:CC
 note: inside `start`
diff --git a/src/tools/miri/tests/fail/alloc/alloc_error_handler_no_std.rs b/src/tools/miri/tests/fail/alloc/alloc_error_handler_no_std.rs
index e3949b889f96..18a8a61f22f6 100644
--- a/src/tools/miri/tests/fail/alloc/alloc_error_handler_no_std.rs
+++ b/src/tools/miri/tests/fail/alloc/alloc_error_handler_no_std.rs
@@ -7,17 +7,17 @@
 extern crate alloc;
 
 use alloc::alloc::*;
+use core::fmt::Write;
 
-extern "Rust" {
-    fn miri_write_to_stderr(bytes: &[u8]);
-}
+#[path = "../../utils/mod.no_std.rs"]
+mod utils;
 
 // The default no_std alloc_error_handler is a panic.
 
 #[panic_handler]
-fn panic_handler(_panic_info: &core::panic::PanicInfo) -> ! {
-    let msg = "custom panic handler called!\n";
-    unsafe { miri_write_to_stderr(msg.as_bytes()) };
+fn panic_handler(panic_info: &core::panic::PanicInfo) -> ! {
+    let _ = writeln!(utils::MiriStderr, "custom panic handler called!");
+    let _ = writeln!(utils::MiriStderr, "{panic_info}");
     core::intrinsics::abort(); //~ERROR: aborted
 }
 
diff --git a/src/tools/miri/tests/fail/alloc/alloc_error_handler_no_std.stderr b/src/tools/miri/tests/fail/alloc/alloc_error_handler_no_std.stderr
index 906c51be8bdd..6b98f6f75d85 100644
--- a/src/tools/miri/tests/fail/alloc/alloc_error_handler_no_std.stderr
+++ b/src/tools/miri/tests/fail/alloc/alloc_error_handler_no_std.stderr
@@ -1,4 +1,6 @@
 custom panic handler called!
+panicked at RUSTLIB/alloc/src/alloc.rs:LL:CC:
+memory allocation of 4 bytes failed
 error: abnormal termination: the program aborted execution
   --> $DIR/alloc_error_handler_no_std.rs:LL:CC
    |
diff --git a/src/tools/miri/tests/fail/panic/no_std.rs b/src/tools/miri/tests/fail/panic/no_std.rs
index 26cc0b278217..4d32b6d74619 100644
--- a/src/tools/miri/tests/fail/panic/no_std.rs
+++ b/src/tools/miri/tests/fail/panic/no_std.rs
@@ -1,27 +1,11 @@
+//@compile-flags: -Cpanic=abort
 #![feature(start, core_intrinsics)]
 #![no_std]
-//@compile-flags: -Cpanic=abort
-
-// Plumbing to let us use `writeln!` to host stderr:
-
-extern "Rust" {
-    fn miri_write_to_stderr(bytes: &[u8]);
-}
-
-struct HostErr;
 
 use core::fmt::Write;
 
-impl Write for HostErr {
-    fn write_str(&mut self, s: &str) -> core::fmt::Result {
-        unsafe {
-            miri_write_to_stderr(s.as_bytes());
-        }
-        Ok(())
-    }
-}
-
-// Aaaand the test:
+#[path = "../../utils/mod.no_std.rs"]
+mod utils;
 
 #[start]
 fn start(_: isize, _: *const *const u8) -> isize {
@@ -30,6 +14,6 @@ fn start(_: isize, _: *const *const u8) -> isize {
 
 #[panic_handler]
 fn panic_handler(panic_info: &core::panic::PanicInfo) -> ! {
-    writeln!(HostErr, "{panic_info}").ok();
+    writeln!(utils::MiriStderr, "{panic_info}").ok();
     core::intrinsics::abort(); //~ ERROR: the program aborted execution
 }
diff --git a/src/tools/miri/tests/pass/no_std.rs b/src/tools/miri/tests/pass/no_std.rs
index 3c98ee50aa9c..fc1c16f5fb95 100644
--- a/src/tools/miri/tests/pass/no_std.rs
+++ b/src/tools/miri/tests/pass/no_std.rs
@@ -2,30 +2,14 @@
 #![feature(start)]
 #![no_std]
 
-// Plumbing to let us use `writeln!` to host stdout:
-
-extern "Rust" {
-    fn miri_write_to_stdout(bytes: &[u8]);
-}
-
-struct Host;
-
 use core::fmt::Write;
 
-impl Write for Host {
-    fn write_str(&mut self, s: &str) -> core::fmt::Result {
-        unsafe {
-            miri_write_to_stdout(s.as_bytes());
-        }
-        Ok(())
-    }
-}
-
-// Aaaand the test:
+#[path = "../utils/mod.no_std.rs"]
+mod utils;
 
 #[start]
 fn start(_: isize, _: *const *const u8) -> isize {
-    writeln!(Host, "hello, world!").unwrap();
+    writeln!(utils::MiriStdout, "hello, world!").unwrap();
     0
 }
 
diff --git a/src/tools/miri/tests/utils/io.rs b/src/tools/miri/tests/utils/io.rs
new file mode 100644
index 000000000000..e3eaa6c468a1
--- /dev/null
+++ b/src/tools/miri/tests/utils/io.rs
@@ -0,0 +1,25 @@
+use core::fmt::{self, Write};
+
+use super::miri_extern;
+
+pub struct MiriStderr;
+
+impl Write for MiriStderr {
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        unsafe {
+            miri_extern::miri_write_to_stderr(s.as_bytes());
+        }
+        Ok(())
+    }
+}
+
+pub struct MiriStdout;
+
+impl Write for MiriStdout {
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        unsafe {
+            miri_extern::miri_write_to_stdout(s.as_bytes());
+        }
+        Ok(())
+    }
+}
diff --git a/src/tools/miri/tests/utils/miri_extern.rs b/src/tools/miri/tests/utils/miri_extern.rs
index e2983f6c71a7..d6c43b188219 100644
--- a/src/tools/miri/tests/utils/miri_extern.rs
+++ b/src/tools/miri/tests/utils/miri_extern.rs
@@ -133,8 +133,8 @@ extern "Rust" {
     /// with a null terminator.
     /// Returns 0 if the `out` buffer was large enough, and the required size otherwise.
     pub fn miri_host_to_target_path(
-        path: *const std::ffi::c_char,
-        out: *mut std::ffi::c_char,
+        path: *const core::ffi::c_char,
+        out: *mut core::ffi::c_char,
         out_size: usize,
     ) -> usize;
 
diff --git a/src/tools/miri/tests/utils/mod.no_std.rs b/src/tools/miri/tests/utils/mod.no_std.rs
new file mode 100644
index 000000000000..aaf2bf50c4e6
--- /dev/null
+++ b/src/tools/miri/tests/utils/mod.no_std.rs
@@ -0,0 +1,11 @@
+#![allow(dead_code)]
+#![allow(unused_imports)]
+
+#[macro_use]
+mod macros;
+
+mod io;
+mod miri_extern;
+
+pub use self::io::*;
+pub use self::miri_extern::*;
diff --git a/src/tools/miri/tests/utils/mod.rs b/src/tools/miri/tests/utils/mod.rs
index cb9380f5753c..138ada4e20d7 100644
--- a/src/tools/miri/tests/utils/mod.rs
+++ b/src/tools/miri/tests/utils/mod.rs
@@ -5,9 +5,11 @@
 mod macros;
 
 mod fs;
+mod io;
 mod miri_extern;
 
 pub use self::fs::*;
+pub use self::io::*;
 pub use self::miri_extern::*;
 
 pub fn run_provenance_gc() {