Add flags for overflow on clang. #120775

AaronRobinsonMSFT · 2025-10-15T23:16:18Z

In clang-20 there is a known breaking change to -fwrapv that impacted us. Details can be found at https://releases.llvm.org/20.1.0/tools/clang/docs/ReleaseNotes.html#potentially-breaking-changes.

Add the -fno-strict-aliasing to match our MSVC usage as well.

Contributes to #119706

In clang-20 there is a known breaking change to -fwrapv that impacted us. Details can be found at https://releases.llvm.org/20.1.0/tools/clang/docs/ReleaseNotes.html#potentially-breaking-changes. Add the -fno-strict-aliasing to match our MSVC usage as well.

AaronRobinsonMSFT · 2025-10-15T23:16:45Z

/cc @rnkovacs

dotnet-policy-service · 2025-10-15T23:17:02Z

Tagging subscribers to this area: @mangod9
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jkotas

LGTM. Thank you!

jkoritzinsky

One of these days I'll get UBSAN working..

jkotas · 2025-10-16T16:56:08Z

We should have a build image with clang 21 now: dotnet/dotnet-buildtools-prereqs-docker#1516

You can try updating all mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0 under eng to mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0 in this PR to check what the CI tests think about it.

am11 · 2025-10-18T06:26:39Z

Last CI run still used clang 20:

  -- The C compiler identification is Clang 20.1.8
  -- The CXX compiler identification is Clang 20.1.8

New images were built a few hours ago dotnet/dotnet-buildtools-prereqs-docker#1516 (comment) (it doesn't automatically rebuild the subtree).

am11 · 2025-10-18T15:44:32Z

@jkotas, looks like we need to apply:

--- a/src/native/libs/System.Security.Cryptography.Native/pal_x509.c
+++ b/src/native/libs/System.Security.Cryptography.Native/pal_x509.c
@@ -1250,6 +1250,7 @@ static int32_t X509ChainVerifyOcsp(X509_STORE_CTX* storeCtx, X509* subject, X509
             {
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wcast-qual"
+#pragma clang diagnostic ignored "-Wimplicit-void-ptr-cast"
                 if (i2d_OCSP_RESPONSE_bio(bio, resp))
 #pragma clang diagnostic pop
                 {

am11 · 2025-10-18T18:55:43Z

FreeBSD build fix:

--- a/src/native/libs/System.Native/pal_interfaceaddresses.c
+++ b/src/native/libs/System.Native/pal_interfaceaddresses.c
@@ -561,7 +561,7 @@ int32_t SystemNative_EnumerateGatewayAddressesForInterface(void* context, uint32
         return -1;
     }
 
-    uint8_t* buffer = malloc(byteCount);
+    uint8_t* buffer = (uint8_t*)malloc(byteCount);
     if (buffer == NULL)
     {
         errno = ENOMEM;
@@ -587,7 +587,7 @@ int32_t SystemNative_EnumerateGatewayAddressesForInterface(void* context, uint32
 
         byteCount = tmpEstimatedSize;
         free(buffer);
-        buffer = malloc(byteCount);
+        buffer = (uint8_t*)malloc(byteCount);
         if (buffer == NULL)
         {
             errno = ENOMEM;

am11 · 2025-10-18T19:59:45Z

It would be nice to update tables in https://github.com/dotnet/runtime/blob/f0db8f9d9668ba03897739152d02623acbd04466/docs/workflow/using-docker.md at the same time (replace net10 with net11). It can be done in a follow-up PR. :)

azure-pipelines · 2025-10-23T14:47:13Z

Azure Pipelines successfully started running 1 pipeline(s).

AaronRobinsonMSFT · 2025-10-23T18:33:21Z

/azp run runtime-coreclr outerloop

azure-pipelines · 2025-10-23T18:33:43Z

Azure Pipelines successfully started running 1 pipeline(s).

AaronRobinsonMSFT · 2025-10-24T01:55:31Z

/ba-g Unrelated failures in outerloop

tmds · 2025-10-24T05:42:56Z

@AaronRobinsonMSFT perhaps this is needed in some other places too: https://github.com/search?q=repo%3Adotnet%2Fdotnet%20-fwrapv&type=code

am11 · 2025-10-24T06:33:42Z

Automated code flow will sync with VMR.

tmds · 2025-10-24T11:34:32Z

@am11 did you click the link? There's some thing for mono, and also in src/deployment-tools and src/diagnostics.

am11 · 2025-10-24T11:39:19Z

We sync eng/native with dotnet/diagnostics from time to time. I can resync it. Not sure if deployment-tools uses these configs.

Updated comments and compile options for signed overflow and strict aliasing. See related code for dotnet/runtime - dotnet/runtime#120775

Updated compiler options to improve signed overflow handling and suppress strict aliasing rules. See related code for dotnet/runtime#120775

Related changes for mono - see #120775

Updated comments and compile options for signed overflow and strict aliasing. See related code for dotnet/runtime - dotnet/runtime#120775

## Customer Impact - [x] Customer reported - [ ] Found internally These issues were reported in #119706 as problems with clang-21 on Fedora 43. The investigation uncovered that clang introduced a potentially breaking change in clang-20 that we do not currently consume. These build changes impact VMR related builds when linux distrobutions performing source build adopt clang-21. clang-20 breaking change log - https://releases.llvm.org/20.1.0/tools/clang/docs/ReleaseNotes.html#potentially-breaking-changes. This PR contains the minimal changes needed to fix issues from the following PRs #120644 and #120775. ## Regression - [x] Yes - [ ] No Moving to the new clang-21 compiler will cause the runtime to crash. This is a regression from using .NET 10 and the default compiler of clang-19. ## Testing This has been validated using various legs and examples to demonstrate the usage of undefined behavior these flags convert into "defined" behavior in C/C++. ## Risk Low. This makes clang-21 more permissive and is limited to non official product builds. --------- Co-authored-by: Jan Kotas <[email protected]>

…0.0 (#121151) ## Customer Impact - [x] Customer reported - [ ] Found internally These issues were reported in #119706 as problems with clang-21 on Fedora 43. The investigation uncovered that clang introduced a potentially breaking change in clang-20 that we do not currently consume. These build changes impact VMR related builds when linux distrobutions performing source build adopt clang-21. clang-20 breaking change log - https://releases.llvm.org/20.1.0/tools/clang/docs/ReleaseNotes.html#potentially-breaking-changes. This PR contains the minimal changes needed to fix issues from the following PR #120775. .NET 10: #121124 .NET 8: #121150 ## Regression - [ ] Yes - [x] No Build with the new clang-21 compiler will cause the runtime to crash. ## Testing This has been validated using various legs and examples to demonstrate the usage of undefined behavior these flags convert into "defined" behavior in C/C++. ## Risk Low. This has zero impact on our production build since we specifically target clang-18. This is only valid for those partners that are using clang-20+.

…0.0 (#121150) ## Customer Impact - [x] Customer reported - [ ] Found internally These issues were reported in #119706 as problems with clang-21 on Fedora 43. The investigation uncovered that clang introduced a potentially breaking change in clang-20 that we do not currently consume. These build changes impact VMR related builds when linux distrobutions performing source build adopt clang-21. clang-20 breaking change log - https://releases.llvm.org/20.1.0/tools/clang/docs/ReleaseNotes.html#potentially-breaking-changes. This PR contains the minimal changes needed to fix issues from the following PR #120775. .NET 10: #121124 .NET 9: #121151 ## Regression - [ ] Yes - [x] No Build with the new clang-21 compiler will cause the runtime to crash. ## Testing This has been validated using various legs and examples to demonstrate the usage of undefined behavior these flags convert into "defined" behavior in C/C++. ## Risk Low. This has zero impact on our production build since we specifically target clang-16. This is only valid for those partners that are using clang-20+.

AaronRobinsonMSFT added this to the 11.0.0 milestone Oct 15, 2025

AaronRobinsonMSFT requested review from jkotas and tmds October 15, 2025 23:16

AaronRobinsonMSFT added the area-VM-coreclr label Oct 15, 2025

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jkotas approved these changes Oct 15, 2025

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AaronRobinsonMSFT mentioned this pull request Oct 16, 2025

.NET crashes when compiled with clang 21.1 on Fedora 43 #119706

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slow macOS - "##[error]The job running on agent Azure Pipelines 9 ran longer than the maximum time of 60 minutes." dotnet/dnceng#1883

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The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#3008

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Update pipeline to newest images.

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jkotas added 2 commits October 17, 2025 23:35

Merge branch 'main' into runtime119706

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Test failure: System.IO.Tests.FileInfo_SymbolicLinks.ResolveLinkTarget_Succeeds #120380

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[android][arm64] System.Net.Sockets.Tests.SendTo_SyncForceNonBlocking.Datagram_UDP_ShouldImplicitlyBindLocalEndpoint fails with NetworkUnreachable #120526

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build-analysis bot mentioned this pull request Oct 18, 2025

Unable to pull image from mcr.microsoft.com #117164

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Fix docs

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[wasm/browser] Failed to connect to socket /run/dbus/system_bus_socket #120176

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Microsoft.Extensions.Hosting.Tests.ConsoleLifetimeExitTests.EnsureEnvironmentExitDoesntHang fails on .NET Framework #119545

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AaronRobinsonMSFT marked this pull request as ready for review October 20, 2025 01:23

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/root/helix/work/correlation/scripts/<hash>/execute.sh: Permission denied dotnet/dnceng#3412

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Timeout in HostFactoryResolverTests.NoSpecialEntryPointPatternCanRunInParallel #114704

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"We stopped hearing from agent Azure Pipelines 32. Verify the agent machine is running and has a healthy network connection" dotnet/dnceng#1886

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AaronRobinsonMSFT merged commit 97669b0 into dotnet:main Oct 24, 2025
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Create Linux build images for .NET 11 #120645

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[main] Source code updates from dotnet/runtime dotnet/dotnet#3103

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[release/10.0] Apply changes for building with clang-21 #121124

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Follow-up clang-21 flags for mono #121125

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AaronRobinsonMSFT mentioned this pull request Oct 27, 2025

Refine compiler options for signed overflow and aliasing dotnet/diagnostics#5618

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AaronRobinsonMSFT mentioned this pull request Oct 27, 2025

Modify compiler options for overflow and aliasing dotnet/deployment-tools#507

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AaronRobinsonMSFT added a commit that referenced this pull request Oct 27, 2025

Follow-up clang-21 flags for mono (#121125)

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Related changes for mono - see #120775

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[release/8.0-staging] Add flags when the clang's major version is > 20.0 #121150

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[release/9.0-staging] Add flags when the clang's major version is > 20.0 #121151

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Add flags for overflow on clang. #120775

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