Printing a raw pointer fails in miri

[jrmuizel]

The following safe code fails to run in Miri:

println!("{:?}", Box::into_raw(Box::new(4)));

error[E0080]: Miri evaluation error: a raw memory access tried to access part of a pointer value as raw bytes
   --> /Users/jrmuizel/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/src/libcore/ops/arith.rs:528:45
    |
528 |             fn rem(self, other: $t) -> $t { self % other }
    |                                             ^^^^^^^^^^^^ Miri evaluation error: a raw memory access tried to access part of a pointer value as raw bytes
    |
    = note: inside call to `<usize as std::ops::Rem>::rem` at /Users/jrmuizel/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/src/libcore/fmt/num.rs:61:25
    = note: inside call to `<core::fmt::num::LowerHex as core::fmt::num::GenericRadix>::fmt_int::<usize>` at /Users/jrmuizel/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/src/libcore/fmt/num.rs:135:46
    = note: inside call to `core::fmt::num::<impl std::fmt::LowerHex for usize>::fmt` at /Users/jrmuizel/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/src/libcore/fmt/mod.rs:2024:19
    = note: inside call to `<*const i32 as std::fmt::Pointer>::fmt` at /Users/jrmuizel/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/src/libcore/fmt/mod.rs:2036:9
    = note: inside call to `<*mut i32 as std::fmt::Pointer>::fmt` at /Users/jrmuizel/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/src/libcore/fmt/mod.rs:2062:54
    = note: inside call to `<*mut i32 as std::fmt::Debug>::fmt` at /Users/jrmuizel/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/src/libcore/fmt/mod.rs:1016:17
    = note: inside call to `std::fmt::write` at /Users/jrmuizel/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/src/libstd/io/mod.rs:1288:15
    = note: inside call to `<tests::test::Sink as std::io::Write>::write_fmt` at /Users/jrmuizel/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/src/libstd/io/impls.rs:141:9
    = note: inside call to `std::io::impls::<impl std::io::Write for std::boxed::Box<dyn std::io::Write + std::marker::Send>>::write_fmt` at /Users/jrmuizel/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/src/libstd/io/stdio.rs:783:24
    = note: inside call to closure at /Users/jrmuizel/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/src/libstd/thread/local.rs:257:16
    = note: inside call to `std::thread::LocalKey::<std::cell::RefCell<std::option::Option<std::boxed::Box<dyn std::io::Write + std::marker::Send>>>>::try_with::<[closure@DefId(1:2736 ~ std[797b]::io[0]::stdio[0]::print_to[0]::{{closure}}[0]) 0:&std::fmt::Arguments, 1:&fn() -> std::io::Stdout], std::result::Result<(), std::io::Error>>` at /Users/jrmuizel/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/src/libstd/io/stdio.rs:780:18
    = note: inside call to `std::io::stdio::print_to::<std::io::Stdout>` at /Users/jrmuizel/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/src/libstd/io/stdio.rs:802:5
note: inside call to `std::io::_print` at <::std::macros::println macros>:2:4
   --> src/lib.rs:5:9
    |
5   |         println!("{:?}", Box::into_raw(Box::new(4)));
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[RalfJung]

@jrmuizel thanks for the report! Could you try to pass a seed, by running Miri with -Zmiri-seed=42?

Currently, letting the program observe the integer base address (which requires #224) is still disabled per default; but in #785 we have a plan for enabling it per default.

[jrmuizel]

Indeed using -Zmiri-seed fixes.

[RalfJung]

Thanks for checking! I am then closing this issue. Enabling raw pointer printing per default is tracked at #785.