Do not allocate or unwind after fork
### Objective scenarios
* Make (simple) panics safe in `Command::pre_exec_hook`, including most `panic!` calls, `Option::unwrap`, and array bounds check failures.
* Make it possible to `libc::fork` and then safely panic in the child (needed for the above, but this requirement means exposing the new raw hook API which the `Command` implementation needs).
* In singlethreaded programs, where panic in `pre_exec_hook` is already memory-safe, prevent the double-unwinding malfunction #79740.
I think we want to make panic after fork safe even though the post-fork child environment is only experienced by users of `unsafe`, beause the subset of Rust in which any panic is UB is really far too hazardous and unnatural.
#### Approach
* Provide a way for a program to, at runtime, switch to having panics abort. This makes it possible to panic without making *any* heap allocations, which is needed because on some platforms malloc is UB in a child forked from a multithreaded program (see https://github.com/rust-lang/rust/pull/80263#issuecomment-774272370, and maybe also the SuS [spec](https://pubs.opengroup.org/onlinepubs/9699919799/functions/fork.html)).
* Make that change in the child spawned by `Command`.
* Document the rules comprehensively enough that a programmer has a fighting chance of writing correct code.
* Test that this all works as expected (and in particular, that there aren't any heap allocations we missed)
Fixes#79740
#### Rejected (or previously attempted) approaches
* Change the panic machinery to be able to unwind without allocating, at least when the payload and message are both `'static`. This seems like it would be even more subtle. Also that is a potentially-hot path which I don't want to mess with.
* Change the existing panic hook mechanism to not convert the message to a `String` before calling the hook. This would be a surprising change for existing code and would not be detected by the type system.
* Provide a `raw_panic_hook` function to intercept panics in a way that doesn't allocate. (That was an earlier version of this MR.)
### History
This MR could be considered a v2 of #80263. Thanks to everyone who commented there. In particular, thanks to `@m-ou-se,` `@Mark-Simulacrum` and `@hyd-dev.` (Tagging you since I think you might be interested in this new MR.) Compared to #80263, this MR has very substantial changes and additions.
Additionally, I have recently (2021-04-20) completely revised this series following very helpful comments from `@m-ou-se.`
r? `@m-ou-se`
Some platforma (eg ARM64) apparently generate SIGTRAP for panic abort!
See eg
https://github.com/rust-lang/rust/pull/81858#issuecomment-840702765
This is probably a bug, but we don't want to entangle this MR with it.
When it's fixed, this commit should be reverted.
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
Add auto traits and clone trait migrations for RFC2229
This PR
- renames the existent RFC2229 migration `disjoint_capture_drop_reorder` to `disjoint_capture_migration`
- add additional migrations for auto traits and clone trait
Closesrust-lang/project-rfc-2229#29Closesrust-lang/project-rfc-2229#28
r? `@nikomatsakis`
Change param name (k to key and v to value) in std::env module
1. When I was reading code the ide displayed `k` and `v`, so I
thought it would be better to show key and value?
2. I noticed var method already uses `key` instead of `k` so it
is more consistent to use `key` instead of `k`?
Thanks
Emit errors/warns on some wrong uses of rustdoc attributes
This PR adds a few diagnostics:
- error if conflicting `#[doc(inline)]`/`#[doc(no_inline)]` are found
- introduce the `invalid_doc_attributes` lint (warn-by-default) which triggers:
- if a crate-level attribute is used on a non-`crate` item
- if `#[doc(inline)]`/`#[doc(no_inline)]` is used on a non-`use` item
The code could probably be improved but I wanted to get feedback first. Also, some of those changes could be considered breaking changes, so I don't know what the procedure would be? ~~And finally, for the warnings, they are currently hard warnings, maybe it would be better to introduce a lint?~~ (EDIT: introduced the `invalid_doc_attributes` lint)
Closes#80275.
r? `@jyn514`
fork fails there. The failure message is confusing: so c.status()
returns an Err, the closure panics, and the test thinks the panic was
propagated from inside the child.
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
Co-authored-by: Mara Bos <m-ou.se@m-ou.se>
Rearrange SGX split module files
In #75979 several inlined modules were split out into multiple files.
This PR keeps the multiple files but moves a few things around to
organize things in a coherent way.
Cleanup of `wasm`
Some more cleanup of `sys`, this time `wasm`
- Reuse `unsupported::args` (functionally equivalent implementation, just an empty iterator).
- Split out `atomics` implementation of `wasm::thread`, the non-`atomics` implementation is reused from `unsupported`.
- Move all of the `atomics` code to a separate directory `wasm/atomics`.
````@rustbot```` label: +T-libs-impl
r? ````@m-ou-se````
In #75979 several inlined modules were split out into multiple files.
This PR keeps the multiple files but moves a few things around to
organize things in a coherent way.
This tests that we can indeed safely panic after fork, both
a raw libc::fork and in a Command pre_exec hook.
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
Co-authored-by: Mara Bos <m-ou.se@m-ou.se>
This is safe (does not involve heap allocation) but we don't yet have
a test to ensure that stays true. That will come in a moment.
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
Co-authored-by: Mara Bos <m-ou.se@m-ou.se>
Unwinding after fork() in the child is UB on some platforms, because
on those (including musl) malloc can be UB in the child of a
multithreaded program, and unwinding must box for the payload.
Even if it's safe, unwinding past fork() in the child causes whatever
traps the unwind to return twice. This is very strange and clearly
not desirable. With the default behaviour of the thread library, this
can even result in a panic in the child being transformed into zero
exit status (ie, success) as seen in the parent!
Fixes#79740.
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
We must change the atomic read on panic entry to `Acquire`, to pick up
a possible an `always_panic` on another thread.
We add `count` to the names of panic_count::get and ::is_zaero,
because now there is another reason why panic ought to maybe abort.
Renaming these ensures that we have checked every call site to ensure
that they don't need further adjustment.
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
Co-authored-by: Mara Bos <m-ou.se@m-ou.se>
Stablize {HashMap,BTreeMap}::into_{keys,values}
I would propose to stabilize `{HashMap,BTreeMap}::into_{keys,values}`( aka. `map_into_keys_values`).
Closes#75294.
Rollup of 11 pull requests
Successful merges:
- #83553 (Update `ptr` docs with regards to `ptr::addr_of!`)
- #84183 (Update RELEASES.md for 1.52.0)
- #84709 (Add doc alias for `chdir` to `std::env::set_current_dir`)
- #84803 (Reduce duplication in `impl_dep_tracking_hash` macros)
- #84808 (Account for unsatisfied bounds in E0599)
- #84843 (use else if in std library )
- #84865 (rustbuild: Pass a `threads` flag that works to windows-gnu lld)
- #84878 (Clarify documentation for `[T]::contains`)
- #84882 (platform-support: Center the contents of the `std` and `host` columns)
- #84903 (Remove `rustc_middle::mir::interpret::CheckInAllocMsg::NullPointerTest`)
- #84913 (Do not ICE on invalid const param)
Failed merges:
r? `@ghost`
`@rustbot` modify labels: rollup
Add doc alias for `chdir` to `std::env::set_current_dir`
Searching for `chdir` in the Rust documentation produces no useful
results.
I wrote some code recently that called `libc::chdir` and manually
handled errors, because I didn't realize that the safe
`std::env::set_current_dir` existed. I searched for `chdir` and
`change_dir` and `change_directory` (the latter two based on the
precedent of unabbreviating set by `create_dir`), and I also read
through `std::fs` expecting to potentially find it there. Given that
none of those led to `std::env::set_current_dir`, I think that provides
sufficient justification to add this specific alias.
Update `ptr` docs with regards to `ptr::addr_of!`
This updates the documentation since `ptr::addr_of!` and `ptr::addr_of_mut!` are now stable. One might remove the distinction between the sections `# On packed structs` and `# Examples`, as the old section on packed structs was primarily to prevent users of doing undefined behavior, which is not necessary anymore.
Technically there is now wrong/outdated documentation on stable, but I don't think this is worth a point release 😉Fixes#83509.
``````````@rustbot`````````` modify labels: T-doc
Move all `sys::ext` modules to `os`
This PR moves all `sys::ext` modules to `os`, centralizing the location of all `os` code and simplifying the dependencies between `os` and `sys`.
Because this also removes all uses `cfg_if!` on publicly exported items, where after #81969 there were still a few left, this should properly work around https://github.com/rust-analyzer/rust-analyzer/issues/6038.
`@rustbot` label: +T-libs-impl
This updates the documentation since `ptr::addr_of!` and
`ptr::addr_of_mut!` are now stable. One might remove the distinction
between the sections `# On packed structs` and `# Examples`, as the old
section on packed structs was primarily to prevent users of doing unde-
fined behavior, which is not necessary anymore.
There is also a new section in "how to obtain a pointer", which referen-
ces the `ptr::addr_of!` macros.
This commit contains squashed commits from code review.
Co-authored-by: Joshua Nelson <joshua@yottadb.com>
Co-authored-by: Mara Bos <m-ou.se@m-ou.se>
Co-authored-by: Soveu <marx.tomasz@gmail.com>
Co-authored-by: Ralf Jung <post@ralfj.de>
