Cannot list environment variables

[shepmaster]

Cargo.toml

[package]
name = "repro"
version = "0.1.0"
authors = ["An Devloper <an.devloper@example.com>"]
edition = "2018"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]

src/main.rs

fn main() {
    std::env::vars_os();
}

Execution

$ cargo +nightly-2019-05-27 run
   Compiling repro v0.1.0 (/private/tmp/repro)
    Finished dev [unoptimized + debuginfo] target(s) in 0.25s
     Running `target/debug/repro`

$ cargo +nightly-2019-05-27 miri
   Compiling repro v0.1.0 (/private/tmp/repro)
error[E0080]: Miri evaluation error: can't call foreign function: _NSGetEnviron
   --> /Users/shep/.rustup/toolchains/nightly-2019-05-27-x86_64-apple-darwin/lib/rustlib/src/rust/src/libstd/sys/unix/os.rs:405:5
    |
405 |     _NSGetEnviron()
    |     ^^^^^^^^^^^^^^^ Miri evaluation error: can't call foreign function: _NSGetEnviron
    |
    = note: inside call to `std::sys::unix::os::environ` at /Users/shep/.rustup/toolchains/nightly-2019-05-27-x86_64-apple-darwin/lib/rustlib/src/rust/src/libstd/sys/unix/os.rs:426:28
    = note: inside call to `std::sys::unix::os::env` at /Users/shep/.rustup/toolchains/nightly-2019-05-27-x86_64-apple-darwin/lib/rustlib/src/rust/src/libstd/env.rs:143:21
note: inside call to `std::env::vars_os` at src/main.rs:2:5
   --> src/main.rs:2:5
    |
2   |     std::env::vars_os();
    |     ^^^^^^^^^^^^^^^^^^^
    = note: inside call to `main` at /Users/shep/.rustup/toolchains/nightly-2019-05-27-x86_64-apple-darwin/lib/rustlib/src/rust/src/libstd/rt.rs:64:34
    = note: inside call to closure at /Users/shep/.rustup/toolchains/nightly-2019-05-27-x86_64-apple-darwin/lib/rustlib/src/rust/src/libstd/rt.rs:52:53
    = note: inside call to closure at /Users/shep/.rustup/toolchains/nightly-2019-05-27-x86_64-apple-darwin/lib/rustlib/src/rust/src/libstd/panicking.rs:293:40
    = note: inside call to `std::panicking::try::do_call::<[closure@DefId(1:5938 ~ std[29d7]::rt[0]::lang_start_internal[0]::{{closure}}[0]) 0:&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe], i32>` at /Users/shep/.rustup/toolchains/nightly-2019-05-27-x86_64-apple-darwin/lib/rustlib/src/rust/src/libstd/panicking.rs:289:5
    = note: inside call to `std::panicking::try::<i32, [closure@DefId(1:5938 ~ std[29d7]::rt[0]::lang_start_internal[0]::{{closure}}[0]) 0:&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe]>` at /Users/shep/.rustup/toolchains/nightly-2019-05-27-x86_64-apple-darwin/lib/rustlib/src/rust/src/libstd/panic.rs:388:9
    = note: inside call to `std::panic::catch_unwind::<[closure@DefId(1:5938 ~ std[29d7]::rt[0]::lang_start_internal[0]::{{closure}}[0]) 0:&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe], i32>` at /Users/shep/.rustup/toolchains/nightly-2019-05-27-x86_64-apple-darwin/lib/rustlib/src/rust/src/libstd/rt.rs:52:25
    = note: inside call to `std::rt::lang_start_internal` at /Users/shep/.rustup/toolchains/nightly-2019-05-27-x86_64-apple-darwin/lib/rustlib/src/rust/src/libstd/rt.rs:64:5
    = note: inside call to `std::rt::lang_start::<()>`

[RalfJung]

This actually fails on Linux as well.

error[E0080]: Miri evaluation error: can't access foreign static: environ
   --> /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/sys/unix/os.rs:411:5
    |
411 |     &mut environ
    |     ^^^^^^^^^^^^ Miri evaluation error: can't access foreign static: environ
    |
    = note: inside call to `std::sys::unix::os::environ` at /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/sys/unix/os.rs:426:28
    = note: inside call to `std::sys::unix::os::env` at /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/env.rs:143:21
note: inside call to `std::env::vars_os` at src/main.rs:2:5
   --> src/main.rs:2:5
    |
2   |     std::env::vars_os();
    |     ^^^^^^^^^^^^^^^^^^^
    = note: inside call to `main` at /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/rt.rs:64:34
    = note: inside call to closure at /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/rt.rs:52:53
    = note: inside call to closure at /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/panicking.rs:293:40
    = note: inside call to `std::panicking::try::do_call::<[closure@DefId(1:5870 ~ std[82ff]::rt[0]::lang_start_internal[0]::{{closure}}[0]) 0:&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe], i32>` at /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/panicking.rs:289:5
    = note: inside call to `std::panicking::try::<i32, [closure@DefId(1:5870 ~ std[82ff]::rt[0]::lang_start_internal[0]::{{closure}}[0]) 0:&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe]>` at /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/panic.rs:388:9
    = note: inside call to `std::panic::catch_unwind::<[closure@DefId(1:5870 ~ std[82ff]::rt[0]::lang_start_internal[0]::{{closure}}[0]) 0:&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe], i32>` at /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/rt.rs:52:25
    = note: inside call to `std::rt::lang_start_internal` at /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/rt.rs:64:5
    = note: inside call to `std::rt::lang_start::<()>`

[oli-obk]

I remember not implementing these. We essentially need to manually create an allocation for our env vars instead of having the current datastructure. This means we have to start emulating all of these platforms' env datastructure

[pvdrz]

Based on the work already done in #894 I could implement this for linux at least and also make it work with communication enabled.

[RalfJung]

This is much harder though if I recall. With this, the interpreted code iterates over some data structure we provide to it, so we have to provide them in the right (platform-specific) format.

I haven't looked into what this takes, but it will very likely be different for macOS, Windows and Linux. If you want to give it a shot, feel free to! Having it for Linux only would be better than not having it at all, I guess, though platform differences are also annoying.

[pvdrz]

I'm going to start working based on the linux's man entry for environ.

Edit: in a fresh new branch with a different PR :D

[pvdrz]

Apparently rust just calls _NSGetEnviron in OSX and environ in other unix platforms but both are handled in the same way. I actually have a mac to test it so I'm going to try to produce the correct *mut *const *const c_char so everything works accordingly.

[RalfJung]

Please really keep it a separate PR this time though. :)

Review complexity scales superlinearly.

[pvdrz]

Hahaha yeah, lesson learned :)

[pvdrz]

After thinking this during the day I think is better to wait for #894 to land first. The utility function defined in shims::env might be used heavily.

I have a question about how environ is actually accessed. Following the trace, I can see that Memory::get_static_alloc is called because in Memory::get the AllocId for environ does not exist inside Memory.alloc_map. Is this supposed to be the case? or when does the AllocId for environ is decided? It looks like miri is looking for an specific AllocId.

Also, I think we need to change the way environment variables are stored inside Evaluator:

Currently we have a HashMap<Vec<u8>, Pointer<Tag>>. Where each Vec<u8> is the name of a variable and Pointer<Tag> points to an allocation with its value.

However, to reproduce environ and _NSGetEnviron we need to build a pointer to strings storing the variables as name=value. I believe this could be easily done by allocating the whole name=value string instead of just the value. Also we would need to have a memory region for the *const *const c_char itself.

This means that we would need to change setenv to allocate the whole name=value string, and keep updated the *const *const c_char (I'm not sure how messy this might be, because we might need to rellocate the whole thing and update all the pointers inside the hashmap from time to time). And change getenv to read just the value part of the allocation.

Another option would be to allocate the whole environment every time (set|unset)env happens and add the *const *const c_char as a field in Evaluator. However, this would mean duplicating all the evironment content.

[oli-obk]

another option is to run libc through the c to rust compiler (and hope it works) and then interpret the *env functions that are now rust code

[RalfJung]

another option is to run libc through the c to rust compiler (and hope it works) and then interpret the *env functions that are now rust code

There's no kill like overkill? ;)

[pvdrz]

This has been a little problematic. I was not able to create the required static without having stacked borrows issues.

[RalfJung]

@christianpoveda do you have your failed attempt still sitting around somewhere? I'm sure it's just a little thing where you have to properly maintain the tags somewhere, or avoid deriving ptrs with different tags, or so.

[pvdrz]

Hmmm I checked my branches and it seems it is gone :( I can try it again soon with new eyes :)