Add functions for building raw slices to libcore

[oli-obk]

implement #36925

[rust-highfive]

r? @joshtriplett

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[rust-highfive]

The job x86_64-gnu-llvm-6.0 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

travis_time:end:0aac4648:start=1557402614815030543,finish=1557402709621061353,duration=94806030810
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout

Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
$ export GCP_CACHE_BUCKET=rust-lang-ci-cache
$ export AWS_ACCESS_KEY_ID=AKIA46X5W6CZEJZ6XT55
---
travis_time:start:test_codegen
Check compiletest suite=codegen mode=codegen (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:20:40] 
[01:20:40] running 143 tests
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[01:20:44] test result: ok. 113 passed; 0 failed; 30 ignored; 0 measured; 0 filtered out
[01:20:44] 
[01:20:44]  finished in 4.653
[01:20:44] travis_fold:end:test_codegen
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travis_time:start:test_assembly
Check compiletest suite=assembly mode=assembly (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:20:46] 
[01:20:46] running 9 tests
[01:20:46] iiiiiiiii
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[01:20:46]  finished in 0.150
[01:20:46] travis_fold:end:test_assembly

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travis_time:start:test_debuginfo
Check compiletest suite=debuginfo mode=debuginfo-both (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:21:02] 
[01:21:02] running 122 tests
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[01:21:32]  finished in 29.882
[01:21:32] travis_fold:end:test_debuginfo

---
[01:31:51] 
[01:31:51] To learn more, run the command again with --verbose.
[01:31:51] 
[01:31:51] 
[01:31:51] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "test" "--target" "x86_64-unknown-linux-gnu" "-j" "4" "--release" "--locked" "--color" "always" "--features" "panic-unwind backtrace" "--manifest-path" "/checkout/src/libstd/Cargo.toml" "-p" "core" "--" "--quiet"
[01:31:51] 
[01:31:51] 
[01:31:51] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:31:51] Build completed unsuccessfully in 0:22:52
[01:31:51] Build completed unsuccessfully in 0:22:52
[01:31:51] make: *** [check] Error 1
[01:31:51] Makefile:48: recipe for target 'check' failed
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:06db6ef0
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Thu May  9 13:23:50 UTC 2019

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[petertodd]

Hmm, I wonder if there's code that would have issues with zero-sized-types and slice lens > isize::MAX? I know I've had that idea as a way to hack in custom DST's; wouldn't surprise me if others did too. Maybe we do need to say that while it's safe to create such a pointer, it's unsafe to dereference one?

…

On May 10, 2019 4:24:48 AM EDT, Oliver Scherer ***@***.***> wrote: oli-obk commented on this pull request. > +/// Performs the same functionality as [`from_raw_parts`], except that a +/// mutable slice is returned. +/// +/// # Panics +/// +/// The total size of the slice should be no +/// larger than `isize::MAX` **bytes** in memory. +/// +/// See the documentation of [`from_raw_parts`] for more details. +/// +/// [`from_raw_parts`]: ../../std/slice/fn.from_raw_parts.html +#[inline] +#[unstable(feature = "slice_from_raw_parts", reason = "recently added", issue = "36925")] +pub fn slice_from_raw_parts_mut<T>(data: *mut T, len: usize) -> *mut [T] { + debug_assert!(mem::size_of::<T>().saturating_mul(len) <= isize::max_value() as usize, + "attempt to create slice covering half the address space"); It's not a safety issue. I mostly thought of it as "you're going into weird places"-territory. There's basically no reason to ever create such raw slices. I should remove the `Panics` note though. This is just a debug assertion that we'd only get on the builders with debug assertions, so it's mostly a sanity test for our own test suite. -- You are receiving this because you commented. Reply to this email directly or view it on GitHub: #60667 (comment)

[bors]

☔ The latest upstream changes (presumably #61274) made this pull request unmergeable. Please resolve the merge conflicts.

[Centril]

r? @sfackler

[sfackler]

LGTM other than the one nit.

[rust-highfive]

The job x86_64-gnu-llvm-6.0 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

travis_time:end:0f045a1a:start=1560928500740750172,finish=1560928501881683377,duration=1140933205
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout

Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
$ export GCP_CACHE_BUCKET=rust-lang-ci-cache
$ export AWS_ACCESS_KEY_ID=AKIA46X5W6CZEJZ6XT55
---
[00:04:45]    Compiling cc v1.0.35
[00:04:45]    Compiling core v0.0.0 (/checkout/src/libcore)
[00:04:45]    Compiling libc v0.2.54
[00:04:45]    Compiling build_helper v0.1.0 (/checkout/src/build_helper)
[00:04:45] error[E0584]: file for module `ptr` found at both ptr.rs and ptr/mod.rs
[00:04:45]     |
[00:04:45] 176 | pub mod ptr;
[00:04:45]     |         ^^^
[00:04:45]     |
[00:04:45]     |
[00:04:45]     = help: delete or rename one of them to remove the ambiguity
[00:04:45] error: aborting due to previous error
[00:04:45] 
[00:04:45] error: Could not compile `core`.
[00:04:45] warning: build failed, waiting for other jobs to finish...

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[oli-obk]

@bors r=sfackler

[bors]

📌 Commit 8b21b07 has been approved by sfackler

[SimonSapin]

When landing a PR that adds a #[unstable(issue = "…")] attribute, please make sure the relevant issue is labelled at S-tracking-issue. This helps put it in the Libs team’s radar. I sometimes look at https://github.com/rust-lang/rust/issues?q=is%3Aopen+is%3Aissue+label%3AC-tracking-issue+label%3AT-libs to find issues in need of attention.