avoid using aligned_alloc; posix_memalign is better-behaved

[RalfJung]

Also there's no reason why wasi should be different than all the other Unixes here.

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[RalfJung]

Is this rounding even still necessary? Looking at the code, I don't see any indication that the size has to be a multiple of the alignment... but also going back in the history I can't see such a requirement, so maybe I am looking at the wrong thing.

Cc @sunfishcode

Or... should we just use posix_memalign on wasi and remove this code path entirely? It seems to exist.

[RalfJung]

Even emmalloc seems to have posix_memalign, so I think we should just use that.
Cc @cuviper

[sunfishcode]

That code in wasi-libc is unmodified upstream musl code, so all musl targets presumably behave the same way.

On the standards side, the behavior of aligned_alloc when size is not a multiple of alignment appears to have been undefined behavior in C11, though it has since been revised in DR460.

[RalfJung]

That code in wasi-libc is unmodified upstream musl code, so all musl targets presumably behave the same way.

Yeah I since realized this rounding up the size was added only for emmalloc, not for the default wasi-libc allocator.

On the standards side, the behavior of aligned_alloc when size is not a multiple of alignment appears to have been undefined behavior in C11, though it has since been revised in DR460.

Correct, it's not been UB since C18 so the old arguments don't apply any more. emmalloc still decides not to support allocations when the size is not a multiple of the alignment, but only when called via aligned_alloc -- as far as I can tell, there's no good reason for that; it supports such requests just fine when they happen via posix_memalign.

aligned_alloc also has the strange requirement that the memory must always be sufficiently aligned for types with fundamental alignment that fit into the requested size... I don't see emmalloc actually do that, but the code is too much for me to follow. We don't rely on that, though, so this wouldn't affect us.

[cuviper]

Using posix_memalign seems ok to me! In emmalloc, they only differ in the up-front checks, then call the same emmalloc_memalign implementation.

https://github.com/WebAssembly/wasi-libc/blob/2f088a99d8437fb980594f4467879555456f447e/emmalloc/emmalloc.c#L910-L915

https://github.com/WebAssembly/wasi-libc/blob/2f088a99d8437fb980594f4467879555456f447e/emmalloc/emmalloc.c#L1265-L1273

(It also seems reasonable that it should now relax that check in aligned_alloc.)

[RalfJung]

I tried to find out why we're using a different function on wasi, and I think it's just a historic coincidence. The commit that added wasi support used aligned_alloc, and then later this got merged with the other Unix codepaths but without changing which function gets called where. So there's no indication here that using posix_memalign on wasi would be a bad idea.

r? @cuviper

[cuviper]

@bors r+ rollup

[bors]

📌 Commit 5cc020d has been approved by cuviper

It is now in the queue for this repository.

[bors]

⌛ Testing commit 5cc020d with merge 4de34b7...

[rust-log-analyzer]

The job x86_64-msvc failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

---- [codegen-units] tests\codegen-units\partitioning\local-inlining.rs stdout ----

error: compilation failed!
status: exit code: 1
command: PATH="C:\a\rust\rust\build\x86_64-pc-windows-msvc\stage2\bin;C:\Program Files (x86)\Windows Kits\10\bin\x64;C:\Program Files (x86)\Windows Kits\10\bin\10.0.22621.0\x64;C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.39.33519\bin\HostX64\x64;C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.39.33519\bin\HostX64\x64;C:\a\rust\rust\build\x86_64-pc-windows-msvc\stage0-bootstrap-tools\x86_64-pc-windows-msvc\release\deps;C:\a\rust\rust\build\x86_64-pc-windows-msvc\stage0\bin;C:\Program Files\PowerShell\7;C:\a\_temp\msys64\mingw64\bin;C:\a\_temp\msys64\usr\local\bin;C:\a\_temp\msys64\usr\bin;C:\a\_temp\msys64\usr\bin;C:\a\rust\rust\ninja;C:\hostedtoolcache\windows\Python\3.12.3\x64\Scripts;C:\hostedtoolcache\windows\Python\3.12.3\x64;C:\a\rust\rust\sccache;C:\a\_temp\setup-msys2;C:\Program Files\MongoDB\Server\5.0\bin;C:\aliyun-cli;C:\vcpkg;C:\Program Files (x86)\NSIS;C:\tools\zstd;C:\Program Files\Mercurial;C:\hostedtoolcache\windows\stack\2.15.5\x64;C:\cabal\bin;C:\ghcup\bin;C:\mingw64\bin;C:\Program Files\dotnet;C:\Program Files\MySQL\MySQL Server 8.0\bin;C:\Program Files\R\R-4.3.3\bin\x64;C:\SeleniumWebDrivers\GeckoDriver;C:\SeleniumWebDrivers\EdgeDriver;C:\SeleniumWebDrivers\ChromeDriver;C:\Program Files (x86)\sbt\bin;C:\Program Files (x86)\GitHub CLI;C:\Program Files\Git\bin;C:\Program Files (x86)\pipx_bin;C:\npm\prefix;C:\hostedtoolcache\windows\go\1.21.9\x64\bin;C:\hostedtoolcache\windows\Python\3.9.13\x64\Scripts;C:\hostedtoolcache\windows\Python\3.9.13\x64;C:\hostedtoolcache\windows\Ruby\3.0.6\x64\bin;C:\Program Files\OpenSSL\bin;C:\tools\kotlinc\bin;C:\hostedtoolcache\windows\Java_Temurin-Hotspot_jdk\8.0.412-8\x64\bin;C:\Program Files\ImageMagick-7.1.1-Q16-HDRI;C:\Program Files\Microsoft SDKs\Azure\CLI2\wbin;C:\ProgramData\kind;C:\ProgramData\docker-compose;C:\ProgramData\Chocolatey\bin;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0;C:\Windows\System32\OpenSSH;C:\Program Files\dotnet;C:\Program Files\PowerShell\7;C:\Program Files\Microsoft\Web Platform Installer;C:\Program Files\Microsoft SQL Server\Client SDK\ODBC\170\Tools\Binn;C:\Program Files\Microsoft SQL Server\150\Tools\Binn;C:\Program Files (x86)\Windows Kits\10\Windows Performance Toolkit;C:\Program Files (x86)\WiX Toolset v3.14\bin;C:\Program Files\Microsoft SQL Server\130\DTS\Binn;C:\Program Files\Microsoft SQL Server\140\DTS\Binn;C:\Program Files\Microsoft SQL Server\150\DTS\Binn;C:\Program Files\Microsoft SQL Server\160\DTS\Binn;C:\Strawberry\c\bin;C:\Strawberry\perl\site\bin;C:\Strawberry\perl\bin;C:\ProgramData\chocolatey\lib\pulumi\tools\Pulumi\bin;C:\Program Files\TortoiseSVN\bin;C:\Program Files\CMake\bin;C:\ProgramData\chocolatey\lib\maven\apache-maven-3.8.7\bin;C:\Program Files\Microsoft Service Fabric\bin\Fabric\Fabric.Code;C:\Program Files\Microsoft SDKs\Service Fabric\Tools\ServiceFabricLocalClusterManager;C:\Program Files\nodejs;C:\Program Files\Git\cmd;C:\Program Files\Git\mingw64\bin;C:\Program Files\Git\usr\bin;C:\Program Files\GitHub CLI;C:\tools\php;C:\Program Files (x86)\sbt\bin;C:\Program Files\Amazon\AWSCLIV2;C:\Program Files\Amazon\SessionManagerPlugin\bin;C:\Program Files\Amazon\AWSSAMCLI\bin;C:\Program Files\Microsoft SQL Server\130\Tools\Binn;C:\Program Files\LLVM\bin;C:\Users\runneradmin\.dotnet\tools;C:\Users\runneradmin\.cargo\bin;C:\Users\runneradmin\AppData\Local\Microsoft\WindowsApps;C:\a\_temp\msys64\usr\bin\site_perl;C:\a\_temp\msys64\usr\bin\vendor_perl;C:\a\_temp\msys64\usr\bin\core_perl" "C:\\a\\rust\\rust\\build\\x86_64-pc-windows-msvc\\stage2\\bin\\rustc.exe" "C:\\a\\rust\\rust\\tests\\codegen-units\\partitioning\\local-inlining.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=C:\\Users\\runneradmin\\.cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=C:\\a\\rust\\rust\\vendor" "--sysroot" "C:\\a\\rust\\rust\\build\\x86_64-pc-windows-msvc\\stage2" "--target=x86_64-pc-windows-msvc" "--check-cfg" "cfg(FALSE)" "-C" "incremental=C:\\a\\rust\\rust\\build\\x86_64-pc-windows-msvc\\test\\codegen-units\\partitioning\\local-inlining\\local-inlining.inc" "-Z" "incremental-verify-ich" "-Z" "human_readable_cgu_names" "-O" "-C" "prefer-dynamic" "--out-dir" "C:\\a\\rust\\rust\\build\\x86_64-pc-windows-msvc\\test\\codegen-units\\partitioning\\local-inlining" "-A" "internal_features" "-Crpath" "-Cdebuginfo=0" "-Lnative=C:\\a\\rust\\rust\\build\\x86_64-pc-windows-msvc\\native\\rust-test-helpers" "-L" "C:\\a\\rust\\rust\\build\\x86_64-pc-windows-msvc\\test\\codegen-units\\partitioning\\local-inlining\\auxiliary" "-Zprint-mono-items=lazy" "-Zinline-in-all-cgus"
--- stdout -------------------------------
MONO_ITEM fn inline::inlined_function @@ local_inlining.8ec87a7fbea559a-user2[Internal] local_inlining.8ec87a7fbea559a-user1[Internal]
MONO_ITEM fn non_user::baz @@ local_inlining.8ec87a7fbea559a-non_user[External]
MONO_ITEM fn user1::foo @@ local_inlining.8ec87a7fbea559a-user1[External]
MONO_ITEM fn user2::bar @@ local_inlining.8ec87a7fbea559a-user2[External]
--- stderr -------------------------------
--- stderr -------------------------------
error: couldn't create a temp dir: Access is denied. (os error 5) at path "C:\\a\\_temp\\msys64\\tmp\\rustcFKhJYE"
error: aborting due to 1 previous error
------------------------------------------


---
test result: FAILED. 40 passed; 1 failed; 3 ignored; 0 measured; 0 filtered out; finished in 1.07s

Some tests failed in compiletest suite=codegen-units mode=codegen-units host=x86_64-pc-windows-msvc target=x86_64-pc-windows-msvc
Build completed unsuccessfully in 0:40:14
make: *** [Makefile:101: ci-msvc-ps1] Error 1
  network time: Wed, 15 May 2024 18:00:28 GMT
##[error]Process completed with exit code 2.
Post job cleanup.
[command]"C:\Program Files\Git\bin\git.exe" version

[bors]

💔 Test failed - checks-actions

[cuviper]

@bors retry