From 787f9f4ab762c54ce7125451460b01000a26cfd7 Mon Sep 17 00:00:00 2001 From: Oliver Schneider Date: Wed, 11 Oct 2017 10:57:30 +0200 Subject: [PATCH 1/2] Prevent fmt::Arguments from being shared across threads Fixes #45197 --- src/libcore/fmt/mod.rs | 1 + src/test/ui/fmt/send-sync.rs | 20 +++++++++++++++++++ src/test/ui/fmt/send-sync.stderr | 34 ++++++++++++++++++++++++++++++++ 3 files changed, 55 insertions(+) create mode 100644 src/test/ui/fmt/send-sync.rs create mode 100644 src/test/ui/fmt/send-sync.stderr diff --git a/src/libcore/fmt/mod.rs b/src/libcore/fmt/mod.rs index 1e45af5b105c9..4b263596ac1bd 100644 --- a/src/libcore/fmt/mod.rs +++ b/src/libcore/fmt/mod.rs @@ -261,6 +261,7 @@ pub struct Formatter<'a> { struct Void { _priv: (), + _oibit_remover: PhantomData<*mut Fn()>, } /// This struct represents the generic "argument" which is taken by the Xprintf diff --git a/src/test/ui/fmt/send-sync.rs b/src/test/ui/fmt/send-sync.rs new file mode 100644 index 0000000000000..bb4f9dfffc754 --- /dev/null +++ b/src/test/ui/fmt/send-sync.rs @@ -0,0 +1,20 @@ +// Copyright 2017 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +fn send(_: T) {} +fn sync(_: T) {} + +fn main() { + // `Cell` is not `Sync`, so `&Cell` is neither `Sync` nor `Send`, + // `std::fmt::Arguments` used to forget this... + let c = std::cell::Cell::new(42); + send(format_args!("{:?}", c)); + sync(format_args!("{:?}", c)); +} diff --git a/src/test/ui/fmt/send-sync.stderr b/src/test/ui/fmt/send-sync.stderr new file mode 100644 index 0000000000000..1ec53d220e963 --- /dev/null +++ b/src/test/ui/fmt/send-sync.stderr @@ -0,0 +1,34 @@ +error[E0277]: the trait bound `*mut std::ops::Fn() + 'static: std::marker::Sync` is not satisfied in `[std::fmt::ArgumentV1<'_>]` + --> $DIR/send-sync.rs:18:5 + | +18 | send(format_args!("{:?}", c)); + | ^^^^ `*mut std::ops::Fn() + 'static` cannot be shared between threads safely + | + = help: within `[std::fmt::ArgumentV1<'_>]`, the trait `std::marker::Sync` is not implemented for `*mut std::ops::Fn() + 'static` + = note: required because it appears within the type `std::marker::PhantomData<*mut std::ops::Fn() + 'static>` + = note: required because it appears within the type `core::fmt::Void` + = note: required because it appears within the type `&core::fmt::Void` + = note: required because it appears within the type `std::fmt::ArgumentV1<'_>` + = note: required because it appears within the type `[std::fmt::ArgumentV1<'_>]` + = note: required because of the requirements on the impl of `std::marker::Send` for `&[std::fmt::ArgumentV1<'_>]` + = note: required because it appears within the type `std::fmt::Arguments<'_>` + = note: required by `send` + +error[E0277]: the trait bound `*mut std::ops::Fn() + 'static: std::marker::Sync` is not satisfied in `std::fmt::Arguments<'_>` + --> $DIR/send-sync.rs:19:5 + | +19 | sync(format_args!("{:?}", c)); + | ^^^^ `*mut std::ops::Fn() + 'static` cannot be shared between threads safely + | + = help: within `std::fmt::Arguments<'_>`, the trait `std::marker::Sync` is not implemented for `*mut std::ops::Fn() + 'static` + = note: required because it appears within the type `std::marker::PhantomData<*mut std::ops::Fn() + 'static>` + = note: required because it appears within the type `core::fmt::Void` + = note: required because it appears within the type `&core::fmt::Void` + = note: required because it appears within the type `std::fmt::ArgumentV1<'_>` + = note: required because it appears within the type `[std::fmt::ArgumentV1<'_>]` + = note: required because it appears within the type `&[std::fmt::ArgumentV1<'_>]` + = note: required because it appears within the type `std::fmt::Arguments<'_>` + = note: required by `sync` + +error: aborting due to 2 previous errors + From dc7de37d995e5922ce3b016c5cc01f5fcd326570 Mon Sep 17 00:00:00 2001 From: Oliver Schneider Date: Wed, 11 Oct 2017 14:33:06 +0200 Subject: [PATCH 2/2] Explain the `_oibit_remover` field --- src/libcore/fmt/mod.rs | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/src/libcore/fmt/mod.rs b/src/libcore/fmt/mod.rs index 4b263596ac1bd..c2ebb419e9e3d 100644 --- a/src/libcore/fmt/mod.rs +++ b/src/libcore/fmt/mod.rs @@ -261,6 +261,13 @@ pub struct Formatter<'a> { struct Void { _priv: (), + /// Erases all oibits, because `Void` erases the type of the object that + /// will be used to produce formatted output. Since we do not know what + /// oibits the real types have (and they can have any or none), we need to + /// take the most conservative approach and forbid all oibits. + /// + /// It was added after #45197 showed that one could share a `!Sync` + /// object across threads by passing it into `format_args!`. _oibit_remover: PhantomData<*mut Fn()>, }