diff --git a/Cargo.lock b/Cargo.lock
index 05d1c2d1eb..fb9faa51d5 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1,6 +1,6 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
-version = 3
+version = 4
 
 [[package]]
 name = "addr2line"
@@ -1080,9 +1080,9 @@ checksum = "42ff0bf0c66b8238c6f3b578df37d0b7848e55df8577b3f74f92a69acceeb825"
 
 [[package]]
 name = "ui_test"
-version = "0.26.5"
+version = "0.27.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "32ee4c40e5a5f9fa6864ff976473e5d6a6e9884b6ce68b40690d9f87e1994c83"
+checksum = "180a1250feba0214b892e22c3a14e9f6688cc084d7b45ec4672106fcb7914641"
 dependencies = [
  "annotate-snippets",
  "anyhow",
diff --git a/Cargo.toml b/Cargo.toml
index cb02914fd9..1266dbb4a8 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -48,8 +48,8 @@ windows-sys = { version = "0.52", features = [
 ] }
 
 [dev-dependencies]
+ui_test = "0.27.1"
 colored = "2"
-ui_test = "0.26.5"
 rustc_version = "0.4"
 regex = "1.5.5"
 tempfile = "3"
diff --git a/tests/fail/function_calls/exported_symbol_bad_unwind1.stderr b/tests/fail/function_calls/exported_symbol_bad_unwind1.stderr
index 5f306cc8ab..a87353a23b 100644
--- a/tests/fail/function_calls/exported_symbol_bad_unwind1.stderr
+++ b/tests/fail/function_calls/exported_symbol_bad_unwind1.stderr
@@ -1,7 +1,6 @@
 thread 'main' panicked at tests/fail/function_calls/exported_symbol_bad_unwind1.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 error: Undefined Behavior: unwinding past a stack frame that does not allow unwinding
   --> tests/fail/function_calls/exported_symbol_bad_unwind1.rs:LL:CC
    |
diff --git a/tests/fail/function_calls/exported_symbol_bad_unwind2.both.stderr b/tests/fail/function_calls/exported_symbol_bad_unwind2.both.stderr
index aef45042e8..364840e925 100644
--- a/tests/fail/function_calls/exported_symbol_bad_unwind2.both.stderr
+++ b/tests/fail/function_calls/exported_symbol_bad_unwind2.both.stderr
@@ -1,7 +1,6 @@
 thread 'main' panicked at tests/fail/function_calls/exported_symbol_bad_unwind2.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 thread 'main' panicked at RUSTLIB/core/src/panicking.rs:LL:CC:
 panic in a function that cannot unwind
 stack backtrace:
diff --git a/tests/fail/function_calls/exported_symbol_bad_unwind2.definition.stderr b/tests/fail/function_calls/exported_symbol_bad_unwind2.definition.stderr
index aef45042e8..364840e925 100644
--- a/tests/fail/function_calls/exported_symbol_bad_unwind2.definition.stderr
+++ b/tests/fail/function_calls/exported_symbol_bad_unwind2.definition.stderr
@@ -1,7 +1,6 @@
 thread 'main' panicked at tests/fail/function_calls/exported_symbol_bad_unwind2.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 thread 'main' panicked at RUSTLIB/core/src/panicking.rs:LL:CC:
 panic in a function that cannot unwind
 stack backtrace:
diff --git a/tests/fail/function_calls/exported_symbol_bad_unwind2.extern_block.stderr b/tests/fail/function_calls/exported_symbol_bad_unwind2.extern_block.stderr
index a81e8226e5..a3c60d3899 100644
--- a/tests/fail/function_calls/exported_symbol_bad_unwind2.extern_block.stderr
+++ b/tests/fail/function_calls/exported_symbol_bad_unwind2.extern_block.stderr
@@ -1,7 +1,6 @@
 thread 'main' panicked at tests/fail/function_calls/exported_symbol_bad_unwind2.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 error: Undefined Behavior: unwinding past a stack frame that does not allow unwinding
   --> tests/fail/function_calls/exported_symbol_bad_unwind2.rs:LL:CC
    |
diff --git a/tests/fail/function_calls/return_pointer_on_unwind.stderr b/tests/fail/function_calls/return_pointer_on_unwind.stderr
index db876cb5ce..f0baf4fdcb 100644
--- a/tests/fail/function_calls/return_pointer_on_unwind.stderr
+++ b/tests/fail/function_calls/return_pointer_on_unwind.stderr
@@ -1,7 +1,6 @@
 thread 'main' panicked at tests/fail/function_calls/return_pointer_on_unwind.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 error: Undefined Behavior: using uninitialized data, but this operation requires initialized memory
   --> tests/fail/function_calls/return_pointer_on_unwind.rs:LL:CC
    |
diff --git a/tests/fail/intrinsics/uninit_uninhabited_type.stderr b/tests/fail/intrinsics/uninit_uninhabited_type.stderr
index ffc3a3eae9..a86b0ff641 100644
--- a/tests/fail/intrinsics/uninit_uninhabited_type.stderr
+++ b/tests/fail/intrinsics/uninit_uninhabited_type.stderr
@@ -1,7 +1,6 @@
 thread 'main' panicked at RUSTLIB/core/src/panicking.rs:LL:CC:
 aborted execution: attempted to instantiate uninhabited type `!`
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 thread caused non-unwinding panic. aborting.
 error: abnormal termination: the program aborted execution
   --> RUSTLIB/std/src/sys/pal/PLATFORM/mod.rs:LL:CC
diff --git a/tests/fail/intrinsics/zero_fn_ptr.stderr b/tests/fail/intrinsics/zero_fn_ptr.stderr
index 49cfc473bd..45ec676ab5 100644
--- a/tests/fail/intrinsics/zero_fn_ptr.stderr
+++ b/tests/fail/intrinsics/zero_fn_ptr.stderr
@@ -1,7 +1,6 @@
 thread 'main' panicked at RUSTLIB/core/src/panicking.rs:LL:CC:
 aborted execution: attempted to zero-initialize type `fn()`, which is invalid
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 thread caused non-unwinding panic. aborting.
 error: abnormal termination: the program aborted execution
   --> RUSTLIB/std/src/sys/pal/PLATFORM/mod.rs:LL:CC
diff --git a/tests/fail/panic/abort_unwind.stderr b/tests/fail/panic/abort_unwind.stderr
index e9c5413693..0c1eaa632e 100644
--- a/tests/fail/panic/abort_unwind.stderr
+++ b/tests/fail/panic/abort_unwind.stderr
@@ -1,7 +1,6 @@
 thread 'main' panicked at tests/fail/panic/abort_unwind.rs:LL:CC:
 PANIC!!!
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 thread 'main' panicked at RUSTLIB/core/src/panicking.rs:LL:CC:
 panic in a function that cannot unwind
 stack backtrace:
diff --git a/tests/fail/panic/bad_unwind.stderr b/tests/fail/panic/bad_unwind.stderr
index c152d1a960..b9b6546656 100644
--- a/tests/fail/panic/bad_unwind.stderr
+++ b/tests/fail/panic/bad_unwind.stderr
@@ -1,7 +1,6 @@
 thread 'main' panicked at tests/fail/panic/bad_unwind.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 error: Undefined Behavior: unwinding past a stack frame that does not allow unwinding
   --> tests/fail/panic/bad_unwind.rs:LL:CC
    |
diff --git a/tests/fail/panic/double_panic.stderr b/tests/fail/panic/double_panic.stderr
index 3e00821796..93533236b4 100644
--- a/tests/fail/panic/double_panic.stderr
+++ b/tests/fail/panic/double_panic.stderr
@@ -1,7 +1,6 @@
 thread 'main' panicked at tests/fail/panic/double_panic.rs:LL:CC:
 first
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 thread 'main' panicked at tests/fail/panic/double_panic.rs:LL:CC:
 second
 stack backtrace:
diff --git a/tests/fail/panic/panic_abort1.stderr b/tests/fail/panic/panic_abort1.stderr
index c5f04d581c..3c870c06cc 100644
--- a/tests/fail/panic/panic_abort1.stderr
+++ b/tests/fail/panic/panic_abort1.stderr
@@ -1,7 +1,6 @@
 thread 'main' panicked at tests/fail/panic/panic_abort1.rs:LL:CC:
 panicking from libstd
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 error: abnormal termination: the program aborted execution
   --> RUSTLIB/panic_abort/src/lib.rs:LL:CC
    |
diff --git a/tests/fail/panic/panic_abort2.stderr b/tests/fail/panic/panic_abort2.stderr
index 535cddfd4d..16d45189f0 100644
--- a/tests/fail/panic/panic_abort2.stderr
+++ b/tests/fail/panic/panic_abort2.stderr
@@ -1,7 +1,6 @@
 thread 'main' panicked at tests/fail/panic/panic_abort2.rs:LL:CC:
 42-panicking from libstd
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 error: abnormal termination: the program aborted execution
   --> RUSTLIB/panic_abort/src/lib.rs:LL:CC
    |
diff --git a/tests/fail/panic/panic_abort3.stderr b/tests/fail/panic/panic_abort3.stderr
index e74cf342e3..7e07ead183 100644
--- a/tests/fail/panic/panic_abort3.stderr
+++ b/tests/fail/panic/panic_abort3.stderr
@@ -1,7 +1,6 @@
 thread 'main' panicked at tests/fail/panic/panic_abort3.rs:LL:CC:
 panicking from libcore
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 error: abnormal termination: the program aborted execution
   --> RUSTLIB/panic_abort/src/lib.rs:LL:CC
    |
diff --git a/tests/fail/panic/panic_abort4.stderr b/tests/fail/panic/panic_abort4.stderr
index 3983d169bd..226560eb0b 100644
--- a/tests/fail/panic/panic_abort4.stderr
+++ b/tests/fail/panic/panic_abort4.stderr
@@ -1,7 +1,6 @@
 thread 'main' panicked at tests/fail/panic/panic_abort4.rs:LL:CC:
 42-panicking from libcore
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 error: abnormal termination: the program aborted execution
   --> RUSTLIB/panic_abort/src/lib.rs:LL:CC
    |
diff --git a/tests/fail/terminate-terminator.stderr b/tests/fail/terminate-terminator.stderr
index e1c0fabd03..00c032d977 100644
--- a/tests/fail/terminate-terminator.stderr
+++ b/tests/fail/terminate-terminator.stderr
@@ -3,7 +3,6 @@ warning: You have explicitly enabled MIR optimizations, overriding Miri's defaul
 thread 'main' panicked at tests/fail/terminate-terminator.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 thread 'main' panicked at RUSTLIB/core/src/panicking.rs:LL:CC:
 panic in a function that cannot unwind
 stack backtrace:
diff --git a/tests/fail/unwind-action-terminate.stderr b/tests/fail/unwind-action-terminate.stderr
index 8183712205..e7a123b03e 100644
--- a/tests/fail/unwind-action-terminate.stderr
+++ b/tests/fail/unwind-action-terminate.stderr
@@ -1,7 +1,6 @@
 thread 'main' panicked at tests/fail/unwind-action-terminate.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 thread 'main' panicked at RUSTLIB/core/src/panicking.rs:LL:CC:
 panic in a function that cannot unwind
 stack backtrace:
diff --git a/tests/panic/alloc_error_handler_hook.stderr b/tests/panic/alloc_error_handler_hook.stderr
index 363298e49d..c1ef50f088 100644
--- a/tests/panic/alloc_error_handler_hook.stderr
+++ b/tests/panic/alloc_error_handler_hook.stderr
@@ -1,5 +1,4 @@
 thread 'main' panicked at tests/panic/alloc_error_handler_hook.rs:LL:CC:
 alloc error hook called
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 yes we are unwinding!
diff --git a/tests/panic/alloc_error_handler_panic.stderr b/tests/panic/alloc_error_handler_panic.stderr
index 2cdff03f10..202325468b 100644
--- a/tests/panic/alloc_error_handler_panic.stderr
+++ b/tests/panic/alloc_error_handler_panic.stderr
@@ -1,5 +1,4 @@
 thread 'main' panicked at RUSTLIB/std/src/alloc.rs:LL:CC:
 memory allocation of 4 bytes failed
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 yes we are unwinding!
diff --git a/tests/panic/div-by-zero-2.stderr b/tests/panic/div-by-zero-2.stderr
index e47a754d38..0d67e94823 100644
--- a/tests/panic/div-by-zero-2.stderr
+++ b/tests/panic/div-by-zero-2.stderr
@@ -1,4 +1,3 @@
 thread 'main' panicked at tests/panic/div-by-zero-2.rs:LL:CC:
 attempt to divide by zero
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
diff --git a/tests/panic/function_calls/exported_symbol_good_unwind.stderr b/tests/panic/function_calls/exported_symbol_good_unwind.stderr
index ec75b6201c..ac8d09f8e6 100644
--- a/tests/panic/function_calls/exported_symbol_good_unwind.stderr
+++ b/tests/panic/function_calls/exported_symbol_good_unwind.stderr
@@ -1,7 +1,6 @@
 thread 'main' panicked at tests/panic/function_calls/exported_symbol_good_unwind.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 thread 'main' panicked at tests/panic/function_calls/exported_symbol_good_unwind.rs:LL:CC:
 explicit panic
 thread 'main' panicked at tests/panic/function_calls/exported_symbol_good_unwind.rs:LL:CC:
diff --git a/tests/panic/oob_subslice.stderr b/tests/panic/oob_subslice.stderr
index d608cec20a..7e265501c8 100644
--- a/tests/panic/oob_subslice.stderr
+++ b/tests/panic/oob_subslice.stderr
@@ -1,4 +1,3 @@
 thread 'main' panicked at tests/panic/oob_subslice.rs:LL:CC:
 range end index 5 out of range for slice of length 4
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
diff --git a/tests/panic/overflowing-lsh-neg.stderr b/tests/panic/overflowing-lsh-neg.stderr
index 29150052b3..b5601ec324 100644
--- a/tests/panic/overflowing-lsh-neg.stderr
+++ b/tests/panic/overflowing-lsh-neg.stderr
@@ -1,4 +1,3 @@
 thread 'main' panicked at tests/panic/overflowing-lsh-neg.rs:LL:CC:
 attempt to shift left with overflow
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
diff --git a/tests/panic/overflowing-rsh-1.stderr b/tests/panic/overflowing-rsh-1.stderr
index 9a71a797da..53feca04ea 100644
--- a/tests/panic/overflowing-rsh-1.stderr
+++ b/tests/panic/overflowing-rsh-1.stderr
@@ -1,4 +1,3 @@
 thread 'main' panicked at tests/panic/overflowing-rsh-1.rs:LL:CC:
 attempt to shift right with overflow
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
diff --git a/tests/panic/overflowing-rsh-2.stderr b/tests/panic/overflowing-rsh-2.stderr
index b671c53c61..44436696fe 100644
--- a/tests/panic/overflowing-rsh-2.stderr
+++ b/tests/panic/overflowing-rsh-2.stderr
@@ -1,4 +1,3 @@
 thread 'main' panicked at tests/panic/overflowing-rsh-2.rs:LL:CC:
 attempt to shift right with overflow
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
diff --git a/tests/panic/panic2.stderr b/tests/panic/panic2.stderr
index 5640bd0b8d..b99422b0b3 100644
--- a/tests/panic/panic2.stderr
+++ b/tests/panic/panic2.stderr
@@ -1,4 +1,3 @@
 thread 'main' panicked at tests/panic/panic2.rs:LL:CC:
 42-panicking from libstd
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
diff --git a/tests/panic/panic3.stderr b/tests/panic/panic3.stderr
index 0114320503..774b8da88e 100644
--- a/tests/panic/panic3.stderr
+++ b/tests/panic/panic3.stderr
@@ -1,4 +1,3 @@
 thread 'main' panicked at tests/panic/panic3.rs:LL:CC:
 panicking from libcore
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
diff --git a/tests/panic/panic4.stderr b/tests/panic/panic4.stderr
index f13b355ea4..e149f5eff6 100644
--- a/tests/panic/panic4.stderr
+++ b/tests/panic/panic4.stderr
@@ -1,4 +1,3 @@
 thread 'main' panicked at tests/panic/panic4.rs:LL:CC:
 42-panicking from libcore
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
diff --git a/tests/panic/transmute_fat2.stderr b/tests/panic/transmute_fat2.stderr
index a9bc0eb9d0..66172aca92 100644
--- a/tests/panic/transmute_fat2.stderr
+++ b/tests/panic/transmute_fat2.stderr
@@ -1,4 +1,3 @@
 thread 'main' panicked at tests/panic/transmute_fat2.rs:LL:CC:
 index out of bounds: the len is 0 but the index is 0
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
diff --git a/tests/panic/unsupported_foreign_function.stderr b/tests/panic/unsupported_foreign_function.stderr
index 278af9612d..402f17bdea 100644
--- a/tests/panic/unsupported_foreign_function.stderr
+++ b/tests/panic/unsupported_foreign_function.stderr
@@ -1,4 +1,3 @@
 thread 'main' panicked at tests/panic/unsupported_foreign_function.rs:LL:CC:
 unsupported Miri functionality: can't call foreign function `foo` on $OS
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
diff --git a/tests/panic/unsupported_syscall.stderr b/tests/panic/unsupported_syscall.stderr
index e9b2b5b665..dc14d2cab8 100644
--- a/tests/panic/unsupported_syscall.stderr
+++ b/tests/panic/unsupported_syscall.stderr
@@ -1,4 +1,3 @@
 thread 'main' panicked at tests/panic/unsupported_syscall.rs:LL:CC:
 unsupported Miri functionality: can't execute syscall with ID 0
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
diff --git a/tests/pass-dep/libc/libc-mem.rs b/tests/pass-dep/libc/libc-mem.rs
index c399616b9a..3d555e737a 100644
--- a/tests/pass-dep/libc/libc-mem.rs
+++ b/tests/pass-dep/libc/libc-mem.rs
@@ -79,13 +79,17 @@ fn test_strcpy() {
 }
 
 fn test_malloc() {
-    // Test that small allocations sometimes *are* not very aligned.
-    let saw_unaligned = (0..64).any(|_| unsafe {
-        let p = libc::malloc(3);
-        libc::free(p);
-        (p as usize) % 4 != 0 // find any that this is *not* 4-aligned
-    });
-    assert!(saw_unaligned);
+    // Real systems may always align to at least a specific power of 2 (like 4 or 8).
+    #[cfg(miri)]
+    {
+        // Test that small allocations sometimes *are* not very aligned.
+        let saw_unaligned = (0..64).any(|_| unsafe {
+            let p = libc::malloc(3);
+            libc::free(p);
+            (p as usize) % 4 != 0 // find any that this is *not* 4-aligned
+        });
+        assert!(saw_unaligned);
+    }
 
     unsafe {
         let p1 = libc::malloc(20);
diff --git a/tests/pass-dep/num_cpus.rs b/tests/pass-dep/num_cpus.rs
index 84339feb11..397f54953f 100644
--- a/tests/pass-dep/num_cpus.rs
+++ b/tests/pass-dep/num_cpus.rs
@@ -1,4 +1,5 @@
 //@compile-flags: -Zmiri-disable-isolation
+//@only-miri: fake cpu number
 
 fn main() {
     assert_eq!(num_cpus::get(), 1);
diff --git a/tests/pass-dep/page_size_override.rs b/tests/pass-dep/page_size_override.rs
index 68858f3875..74ea101b23 100644
--- a/tests/pass-dep/page_size_override.rs
+++ b/tests/pass-dep/page_size_override.rs
@@ -1,4 +1,5 @@
 //@compile-flags: -Zmiri-force-page-size=8
+//@only-miri: fake page size
 
 fn main() {
     let page_size = page_size::get();
diff --git a/tests/pass/panic/catch_panic.stderr b/tests/pass/panic/catch_panic.stderr
index cb74312a83..5241b60887 100644
--- a/tests/pass/panic/catch_panic.stderr
+++ b/tests/pass/panic/catch_panic.stderr
@@ -1,7 +1,6 @@
 thread 'main' panicked at tests/pass/panic/catch_panic.rs:LL:CC:
 Hello from std::panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 Caught panic message (&str): Hello from std::panic
 thread 'main' panicked at tests/pass/panic/catch_panic.rs:LL:CC:
 Hello from std::panic: 1
diff --git a/tests/pass/panic/concurrent-panic.stderr b/tests/pass/panic/concurrent-panic.stderr
index 9c87489e8d..0e7940053b 100644
--- a/tests/pass/panic/concurrent-panic.stderr
+++ b/tests/pass/panic/concurrent-panic.stderr
@@ -3,7 +3,6 @@ Thread 1 reported it has started
 thread '<unnamed>' panicked at tests/pass/panic/concurrent-panic.rs:LL:CC:
 panic in thread 2
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 Thread 2 blocking on thread 1
 Thread 2 reported it has started
 Unlocking mutex
diff --git a/tests/pass/panic/nested_panic_caught.stderr b/tests/pass/panic/nested_panic_caught.stderr
index e066f7dfce..b05d8d070d 100644
--- a/tests/pass/panic/nested_panic_caught.stderr
+++ b/tests/pass/panic/nested_panic_caught.stderr
@@ -1,7 +1,6 @@
 thread 'main' panicked at tests/pass/panic/nested_panic_caught.rs:LL:CC:
 once
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 thread 'main' panicked at tests/pass/panic/nested_panic_caught.rs:LL:CC:
 twice
 stack backtrace:
diff --git a/tests/pass/panic/thread_panic.stderr b/tests/pass/panic/thread_panic.stderr
index 9464e76b6c..4baf7e45fd 100644
--- a/tests/pass/panic/thread_panic.stderr
+++ b/tests/pass/panic/thread_panic.stderr
@@ -1,6 +1,5 @@
 thread '<unnamed>' panicked at tests/pass/panic/thread_panic.rs:LL:CC:
 Hello!
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 thread 'childthread' panicked at tests/pass/panic/thread_panic.rs:LL:CC:
 Hello, world!
diff --git a/tests/ui.rs b/tests/ui.rs
index 9553a37c9a..2b6044aa49 100644
--- a/tests/ui.rs
+++ b/tests/ui.rs
@@ -9,15 +9,22 @@ use colored::*;
 use regex::bytes::Regex;
 use ui_test::build_manager::BuildManager;
 use ui_test::color_eyre::eyre::{Context, Result};
+use ui_test::custom_flags::Flag;
 use ui_test::custom_flags::edition::Edition;
+use ui_test::custom_flags::run::Run;
 use ui_test::dependencies::DependencyBuilder;
-use ui_test::per_test_config::TestConfig;
+use ui_test::per_test_config::{Comments, Condition, TestConfig};
 use ui_test::spanned::Spanned;
-use ui_test::{CommandBuilder, Config, Format, Match, OutputConflictHandling, status_emitter};
+use ui_test::{
+    CommandBuilder, Config, Errored, Format, Match, ignore_output_conflict, status_emitter,
+};
 
 #[derive(Copy, Clone, Debug)]
 enum Mode {
-    Pass,
+    Pass {
+        /// Whether to compile and run with rustc instead of miri
+        rustc: bool,
+    },
     /// Requires annotations
     Fail,
     /// Not used for tests, but for `miri run --dep`
@@ -81,9 +88,18 @@ fn build_native_lib() -> PathBuf {
     native_lib_path
 }
 
+struct WithDependencies {
+    bless: bool,
+}
+
 /// Does *not* set any args or env vars, since it is shared between the test runner and
 /// run_dep_mode.
-fn miri_config(target: &str, path: &str, mode: Mode, with_dependencies: bool) -> Config {
+fn miri_config(
+    target: &str,
+    path: &str,
+    mode: Mode,
+    with_dependencies: Option<WithDependencies>,
+) -> Config {
     // Miri is rustc-like, so we create a default builder for rustc and modify it
     let mut program = CommandBuilder::rustc();
     program.program = miri_path();
@@ -98,8 +114,89 @@ fn miri_config(target: &str, path: &str, mode: Mode, with_dependencies: bool) ->
         ..Config::rustc(path)
     };
 
+    if let Mode::Pass { rustc: true } = mode {
+        config.comment_defaults.base().add_custom("run", Run {
+            exit_code: 0,
+            output_conflict_handling: Some(|path, actual, errors, config| {
+                let path = path.with_file_name(
+                    path.file_name().unwrap().to_str().unwrap().replace(".run.", "."),
+                );
+                // Blessing is only allowed in miri mode, rustc mode must match
+                ui_test::error_on_output_conflict(&path, actual, errors, config);
+            }),
+        });
+        config.program.envs.push(("MIRI_BE_RUSTC".into(), Some("host".into())));
+
+        #[derive(Debug)]
+        struct Strip;
+
+        impl Flag for Strip {
+            fn clone_inner(&self) -> Box<dyn Flag> {
+                Box::new(Strip)
+            }
+
+            fn must_be_unique(&self) -> bool {
+                true
+            }
+
+            fn apply(
+                &self,
+                cmd: &mut Command,
+                _config: &TestConfig,
+                _build_manager: &BuildManager,
+            ) -> Result<(), Errored> {
+                let mut c = Command::new(cmd.get_program());
+                for (k, v) in cmd.get_envs() {
+                    match v {
+                        Some(v) => c.env(k, v),
+                        None => c.env_remove(k),
+                    };
+                }
+                if let Some(dir) = cmd.get_current_dir() {
+                    c.current_dir(dir);
+                }
+                c.args(
+                    cmd.get_args().filter(|arg| !arg.as_encoded_bytes().starts_with(b"-Zmiri-")),
+                );
+                *cmd = c;
+                Ok(())
+            }
+
+            fn test_condition(
+                &self,
+                _config: &Config,
+                comments: &Comments,
+                revision: &str,
+            ) -> bool {
+                for rev in comments.for_revision(revision) {
+                    for arg in &rev.compile_flags {
+                        // A real execution will preempt, and thus behave differently
+                        if arg.starts_with("-Zmiri-preemption-rate") {
+                            return true;
+                        }
+                        // FIXME: can probably support these somehow
+                        if arg.starts_with("-Zmiri-env") {
+                            return true;
+                        }
+                    }
+                }
+                false
+            }
+        }
+
+        config.comment_defaults.base().add_custom("strip_dash_z_miri", Strip);
+
+        // Only run on no target if `only-miri` is passed.
+        config
+            .custom_comments
+            .insert("only-miri", |parser, _, _| parser.only.push(Condition::Target(vec![])));
+    } else {
+        // Nop, we are in miri mode
+        config.custom_comments.insert("only-miri", |_, _, _| {});
+    }
+
     config.comment_defaults.base().exit_status = match mode {
-        Mode::Pass => Some(0),
+        Mode::Pass { .. } => Some(0),
         Mode::Fail => Some(1),
         Mode::RunDep => None,
         Mode::Panic => Some(101),
@@ -118,21 +215,27 @@ fn miri_config(target: &str, path: &str, mode: Mode, with_dependencies: bool) ->
     // keep in sync with `./miri run`
     config.comment_defaults.base().add_custom("edition", Edition("2021".into()));
 
-    if with_dependencies {
+    if let Some(WithDependencies { bless }) = with_dependencies {
+        let program = match mode {
+            Mode::Pass { rustc: true } => CommandBuilder::cargo(),
+            _ =>
+                CommandBuilder {
+                    // Set the `cargo-miri` binary, which we expect to be in the same folder as the `miri` binary.
+                    // (It's a separate crate, so we don't get an env var from cargo.)
+                    program: miri_path()
+                        .with_file_name(format!("cargo-miri{}", env::consts::EXE_SUFFIX)),
+                    // There is no `cargo miri build` so we just use `cargo miri run`.
+                    args: ["miri", "run"].into_iter().map(Into::into).collect(),
+                    // Reset `RUSTFLAGS` to work around <https://github.com/rust-lang/rust/pull/119574#issuecomment-1876878344>.
+                    envs: vec![("RUSTFLAGS".into(), None)],
+                    ..CommandBuilder::cargo()
+                },
+        };
         config.comment_defaults.base().set_custom("dependencies", DependencyBuilder {
-            program: CommandBuilder {
-                // Set the `cargo-miri` binary, which we expect to be in the same folder as the `miri` binary.
-                // (It's a separate crate, so we don't get an env var from cargo.)
-                program: miri_path()
-                    .with_file_name(format!("cargo-miri{}", env::consts::EXE_SUFFIX)),
-                // There is no `cargo miri build` so we just use `cargo miri run`.
-                args: ["miri", "run"].into_iter().map(Into::into).collect(),
-                // Reset `RUSTFLAGS` to work around <https://github.com/rust-lang/rust/pull/119574#issuecomment-1876878344>.
-                envs: vec![("RUSTFLAGS".into(), None)],
-                ..CommandBuilder::cargo()
-            },
+            program,
             crate_manifest_path: Path::new("test_dependencies").join("Cargo.toml"),
             build_std: None,
+            bless_lockfile: bless,
         });
     }
     config
@@ -145,23 +248,56 @@ fn run_tests(
     with_dependencies: bool,
     tmpdir: &Path,
 ) -> Result<()> {
+    // Handle command-line arguments.
+    let mut args = ui_test::Args::test()?;
+    args.bless |= env::var_os("RUSTC_BLESS").is_some_and(|v| v != "0");
+
+    let with_dependencies = with_dependencies.then_some(WithDependencies { bless: args.bless });
+
     let mut config = miri_config(target, path, mode, with_dependencies);
+    config.with_args(&args);
+    if let Mode::Pass { rustc: true } = mode {
+        config.fill_host_and_target()?;
+        // Rustc mode only works on the host
+        if !config.host_matches_target() {
+            return Ok(());
+        }
+        config.output_conflict_handling = ui_test::ignore_output_conflict;
+
+        config.bless_command =
+            Some("add `//@only-miri:` to the test if it cannot be run on the host directly".into());
+    } else {
+        config.bless_command = Some("./miri test --bless".into());
+    }
+
+    if env::var_os("MIRI_SKIP_UI_CHECKS").is_some() {
+        assert!(!args.bless, "cannot use RUSTC_BLESS and MIRI_SKIP_UI_CHECKS at the same time");
+        config.output_conflict_handling = ignore_output_conflict;
+    }
 
     // Add a test env var to do environment communication tests.
     config.program.envs.push(("MIRI_ENV_VAR_TEST".into(), Some("0".into())));
     // Let the tests know where to store temp files (they might run for a different target, which can make this hard to find).
     config.program.envs.push(("MIRI_TEMP".into(), Some(tmpdir.to_owned().into())));
-    // If a test ICEs, we want to see a backtrace.
-    config.program.envs.push(("RUST_BACKTRACE".into(), Some("1".into())));
 
     // Add some flags we always want.
-    config.program.args.push(
-        format!(
-            "--sysroot={}",
-            env::var("MIRI_SYSROOT").expect("MIRI_SYSROOT must be set to run the ui test suite")
-        )
-        .into(),
-    );
+    match mode {
+        // rustc mode doesn't want miri specific flags
+        Mode::Pass { rustc: true } => {}
+        _ => {
+            // If a test ICEs, we want to see a backtrace.
+            config.program.envs.push(("RUST_BACKTRACE".into(), Some("1".into())));
+            config.program.args.push(
+                format!(
+                    "--sysroot={}",
+                    env::var("MIRI_SYSROOT")
+                        .expect("MIRI_SYSROOT must be set to run the ui test suite")
+                )
+                .into(),
+            );
+        }
+    }
+
     config.program.args.push("-Dwarnings".into());
     config.program.args.push("-Dunused".into());
     config.program.args.push("-Ainternal_features".into());
@@ -181,16 +317,6 @@ fn run_tests(
         config.program.args.push(flag);
     }
 
-    // Handle command-line arguments.
-    let mut args = ui_test::Args::test()?;
-    args.bless |= env::var_os("RUSTC_BLESS").is_some_and(|v| v != "0");
-    config.with_args(&args);
-    config.bless_command = Some("./miri test --bless".into());
-
-    if env::var_os("MIRI_SKIP_UI_CHECKS").is_some() {
-        assert!(!args.bless, "cannot use RUSTC_BLESS and MIRI_SKIP_UI_CHECKS at the same time");
-        config.output_conflict_handling = OutputConflictHandling::Ignore;
-    }
     eprintln!("   Compiler: {}", config.program.display());
     ui_test::run_tests_generic(
         // Only run one test suite. In the future we can add all test suites to one `Vec` and run
@@ -261,11 +387,13 @@ regexes! {
     // Windows file paths
     r"\\"                           => "/",
     // erase Rust stdlib path
-    "[^ \n`]*/(rust[^/]*|checkout)/library/" => "RUSTLIB/",
+    "[^ \n`]*/(rust[^/]*|checkout|rustc/[0-9a-f]+)/library/" => "RUSTLIB/",
     // erase platform file paths
     "sys/pal/[a-z]+/"                    => "sys/pal/PLATFORM/",
     // erase paths into the crate registry
     r"[^ ]*/\.?cargo/registry/.*/(.*\.rs)"  => "CARGO_REGISTRY/.../$1",
+    // erase extra panic message that actual runtime code doesn't have
+    "note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect\n" => "",
 }
 
 enum Dependencies {
@@ -312,13 +440,21 @@ fn main() -> Result<()> {
         }
     }
 
-    ui(Mode::Pass, "tests/pass", &target, WithoutDependencies, tmpdir.path())?;
-    ui(Mode::Pass, "tests/pass-dep", &target, WithDependencies, tmpdir.path())?;
+    ui(Mode::Pass { rustc: false }, "tests/pass", &target, WithoutDependencies, tmpdir.path())?;
+    for rustc in [false, true] {
+        ui(Mode::Pass { rustc }, "tests/pass-dep", &target, WithDependencies, tmpdir.path())?;
+    }
     ui(Mode::Panic, "tests/panic", &target, WithDependencies, tmpdir.path())?;
     ui(Mode::Fail, "tests/fail", &target, WithoutDependencies, tmpdir.path())?;
     ui(Mode::Fail, "tests/fail-dep", &target, WithDependencies, tmpdir.path())?;
     if cfg!(unix) {
-        ui(Mode::Pass, "tests/native-lib/pass", &target, WithoutDependencies, tmpdir.path())?;
+        ui(
+            Mode::Pass { rustc: false },
+            "tests/native-lib/pass",
+            &target,
+            WithoutDependencies,
+            tmpdir.path(),
+        )?;
         ui(Mode::Fail, "tests/native-lib/fail", &target, WithoutDependencies, tmpdir.path())?;
     }
 
@@ -326,7 +462,8 @@ fn main() -> Result<()> {
 }
 
 fn run_dep_mode(target: String, args: impl Iterator<Item = OsString>) -> Result<()> {
-    let mut config = miri_config(&target, "", Mode::RunDep, /* with dependencies */ true);
+    let mut config =
+        miri_config(&target, "", Mode::RunDep, Some(WithDependencies { bless: false }));
     config.comment_defaults.base().custom.remove("edition"); // `./miri` adds an `--edition` in `args`, so don't set it twice
     config.fill_host_and_target()?;
     config.program.args = args.collect();