Use read_unaligned instead of read in transmute_copy

[newpavlov]

Closes: #55044

This change could result in performance regression on non-x86 platforms. (but it also can fix some of UB which lurks in existing programs) An alternative would be to update transmute_copy documentation with alignment requirements.

[rust-highfive]

r? @withoutboats

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[nagisa]

This seems like the right thing to do to me…

[newpavlov]

@withoutboats
Any news on this?

[TimNN]

Ping from triage @withoutboats / @rust-lang/libs: This PR requires your review.

[alexcrichton]

@rfcbot fcp merge

I would personally agree that these semantics are correct for this function, not requiring the alignments match up. I'd like to make sure others agree, though

[rfcbot]

Team member @alexcrichton has proposed to merge this. The next step is review by the rest of the tagged teams:

• @Kimundi
• @SimonSapin
• @alexcrichton
• @dtolnay
• @sfackler
• @withoutboats

No concerns currently listed.

Once a majority of reviewers approve (and none object), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

[sfackler]

If we're worried about the performance we can always compare the source and target alignments and call read/read_unaligned as appropriate. It'll all get constant folded out.

[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[alexcrichton]

@bors: r+

[bors]

📌 Commit 4210cca has been approved by alexcrichton

[bors]

⌛ Testing commit 4210cca with merge 90b4a012ad212427dd1c0e3ab72c2ea24bfd0013...

[bors]

💔 Test failed - status-travis

[rust-highfive]

The job arm-android 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.

[01:45:42] test string::test_str_truncate ... ok
[01:45:42] test string::test_str_truncate_invalid_len ... ok
[01:45:42] test string::test_str_truncate_split_codepoint ... ok
[01:45:42] test str::test_unsafe_slice ... ok
[01:45:42] died due to signal 11
[01:45:42] error: test failed, to rerun pass '--test collectionstests'
[01:45:42] 
[01:45:42] 
[01:45:42] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "test" "--target" "arm-linux-androideabi" "-j" "4" "--release" "--locked" "--color" "always" "--features" "panic-unwind backtrace" "--manifest-path" "/checkout/src/libstd/Cargo.toml" "-p" "alloc" "--"
[01:45:42] 
[01:45:42] 
[01:45:42] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test --target arm-linux-androideabi
[01:45:42] Build completed unsuccessfully in 1:31:43
---
travis_time:end:253cf131:start=1542048836960776801,finish=1542048836981431758,duration=20654957
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:012028e4
$ ln -s . checkout && for CORE in obj/cores/core.*; do EXE=$(echo $CORE | sed 's|obj/cores/core\.[0-9]*\.!checkout!\(.*\)|\1|;y|!|/|'); if [ -f "$EXE" ]; then printf travis_fold":start:crashlog\n\033[31;1m%s\033[0m\n" "$CORE"; gdb --batch -q -c "$CORE" "$EXE" -iex 'set auto-load off' -iex 'dir src/' -iex 'set sysroot .' -ex bt -ex q; echo travis_fold":"end:crashlog; fi; done || true
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:256ddeec
travis_time:start:256ddeec
$ cat ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
cat: ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers: No such file or directory
travis_fold:end:after_failure.5
travis_fold:start:after_failure.6
travis_time:start:153396cd
$ dmesg | grep -i kill

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)

[alexcrichton]

@bors: retry

• "died due to signal 11" in collectionstests on arm-android #55861

[bors]

⌛ Testing commit 4210cca with merge c4371c8...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: alexcrichton
Pushing c4371c8 to master...

[rust-highfive]

📣 Toolstate changed by #55052!

Tested on commit c4371c8.
Direct link to PR: #55052

💔 rls on linux: test-pass → test-fail (cc @nrc @Xanewok, @rust-lang/infra).

[kennytm]

The RLS test failure is:

[01:26:21] failures:
[01:26:21] 
[01:26:21] ---- cmd_changing_workspace_lib_retains_bin_diagnostics stdout ----
[01:26:21] thread 'cmd_changing_workspace_lib_retains_bin_diagnostics' panicked at 'assertion failed: `(left == right)`
[01:26:21]   left: `String("E0425")`,
[01:26:21]  right: `"unused_variables"`', tools/rls/tests/tests.rs:408:5
[01:26:21] note: Run with `RUST_BACKTRACE=1` for a backtrace.
[01:26:21] ---rls-stdout---

[nrc]

💔 rls on linux: test-pass → test-fail (cc @nrc @Xanewok, @rust-lang/infra).

Well. That is surprising.