Add compiler flags for clang-21. (#120775)

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

---------

Co-authored-by: Jan Kotas <[email protected]>

Author: AaronRobinsonMSFT

docs/workflow/using-docker.md

@@ -26,27 +26,27 @@ The main Docker images are the most commonly used ones, and the ones you will pr
 
 | Host OS           | Target OS    | Target Arch     | Image                                                                                  | crossrootfs dir      |
 | ----------------- | ------------ | --------------- | -------------------------------------------------------------------------------------- | -------------------- |
-| Azure Linux (x64) | Alpine 3.17  | x64             | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-amd64-musl` | `/crossrootfs/x64`   |
-| Azure Linux (x64) | Ubuntu 18.04 | x64             | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-amd64`        | `/crossrootfs/x64`   |
-| Azure Linux (x64) | Alpine 3.17  | Arm32 (armhf)   | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-arm-musl`   | `/crossrootfs/arm`   |
-| Azure Linux (x64) | Ubuntu 22.04 | Arm32 (armhf)   | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-arm`          | `/crossrootfs/arm`   |
-| Azure Linux (x64) | Alpine 3.17  | Arm64 (arm64v8) | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-arm64-musl` | `/crossrootfs/arm64` |
-| Azure Linux (x64) | Ubuntu 18.04 | Arm64 (arm64v8) | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-arm64`        | `/crossrootfs/arm64` |
-| Azure Linux (x64) | Ubuntu 18.04 | x86             | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-x86`          | `/crossrootfs/x86`   |
+| Azure Linux (x64) | Alpine 3.17  | x64             | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64-musl` | `/crossrootfs/x64`   |
+| Azure Linux (x64) | Ubuntu 18.04 | x64             | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64`        | `/crossrootfs/x64`   |
+| Azure Linux (x64) | Alpine 3.17  | Arm32 (armhf)   | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-arm-musl`   | `/crossrootfs/arm`   |
+| Azure Linux (x64) | Ubuntu 22.04 | Arm32 (armhf)   | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-arm`          | `/crossrootfs/arm`   |
+| Azure Linux (x64) | Alpine 3.17  | Arm64 (arm64v8) | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-arm64-musl` | `/crossrootfs/arm64` |
+| Azure Linux (x64) | Ubuntu 18.04 | Arm64 (arm64v8) | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-arm64`        | `/crossrootfs/arm64` |
+| Azure Linux (x64) | Ubuntu 18.04 | x86             | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-x86`          | `/crossrootfs/x86`   |
 
 **Extended Docker Images**
 
 | Host OS           | Target OS                  | Target Arch   | Image                                                                                   | crossrootfs dir        |
 | ----------------- | -------------------------- | ------------- | --------------------------------------------------------------------------------------- | ---------------------- |
-| Azure Linux (x64) | Android Bionic             | x64           | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-android-amd64` |        *N/A*           |
-| Azure Linux (x64) | Android Bionic (w/OpenSSL) | x64           | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-android-openssl`     |        *N/A*           |
-| Azure Linux (x64) | Android Bionic (w/Docker)  | x64           | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-android-docker`      |        *N/A*           |
-| Azure Linux (x64) | FreeBSD 14                 | x64           | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-freebsd-14`    | `/crossrootfs/x64`     |
-| Azure Linux (x64) | Ubuntu 18.04               | PPC64le       | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-ppc64le`       | `/crossrootfs/ppc64le` |
-| Azure Linux (x64) | Ubuntu 24.04               | RISC-V        | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-riscv64`       | `/crossrootfs/riscv64` |
-| Azure Linux (x64) | Debian sid                 | LoongArch     | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-loongarch64`   | `/crossrootfs/loongarch64` |
-| Azure Linux (x64) | Ubuntu 18.04               | S390x         | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-s390x`         | `/crossrootfs/s390x`   |
-| Azure Linux (x64) | Ubuntu 18.04 (Wasm)        | x64           | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-webassembly-amd64`   | `/crossrootfs/x64`     |
+| Azure Linux (x64) | Android Bionic             | x64           | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-android-amd64` |        *N/A*           |
+| Azure Linux (x64) | Android Bionic (w/OpenSSL) | x64           | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-android-openssl`     |        *N/A*           |
+| Azure Linux (x64) | Android Bionic (w/Docker)  | x64           | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-android-docker`      |        *N/A*           |
+| Azure Linux (x64) | FreeBSD 14                 | x64           | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-freebsd-14`    | `/crossrootfs/x64`     |
+| Azure Linux (x64) | Ubuntu 18.04               | PPC64le       | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-ppc64le`       | `/crossrootfs/ppc64le` |
+| Azure Linux (x64) | Ubuntu 24.04               | RISC-V        | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-riscv64`       | `/crossrootfs/riscv64` |
+| Azure Linux (x64) | Debian sid                 | LoongArch     | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-loongarch64`   | `/crossrootfs/loongarch64` |
+| Azure Linux (x64) | Ubuntu 18.04               | S390x         | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-s390x`         | `/crossrootfs/s390x`   |
+| Azure Linux (x64) | Ubuntu 18.04 (Wasm)        | x64           | `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-webassembly-amd64`   | `/crossrootfs/x64`     |
 | Debian (x64)      | Debian 12                  | x64           | `mcr.microsoft.com/dotnet-buildtools/prereqs:debian-12-gcc15-amd64`                     |        *N/A*           |
 | Ubuntu (x64)      | Tizen 9.0                  | Arm32 (armel) | `mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-22.04-cross-armel-tizen`            | `/crossrootfs/armel`   |
 
@@ -59,7 +59,7 @@ docker run --rm \
   -v <RUNTIME_REPO_PATH>:/runtime \
   -w /runtime \
   -e ROOTFS_DIR=/crossrootfs/x64/ \
-  mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-amd64 \
+  mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64 \
   ./build.sh -s clr --cross -c Checked
 ```
 
@@ -69,7 +69,7 @@ Now, dissecting the command:
 - `-v <RUNTIME_REPO_PATH>:/runtime`: Mount the runtime repo clone located in `<RUNTIME_REPO_PATH>` to the container path `/runtime`.
 - `-w /runtime`: Start the container in the `/runtime` directory.
 - `-e ROOTFS_DIR=/crossrootfs/x64/` sets up the environment variable for crossbuilding.
-- `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-amd64`: The fully qualified name of the Docker image to download. In this case, we want to use an *Azure Linux* image to target the *x64* architecture.
+- `mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64`: The fully qualified name of the Docker image to download. In this case, we want to use an *Azure Linux* image to target the *x64* architecture.
 - `./build.sh -s clr --cross -c Checked`: The build command to run in the repo. In this case, we want to build the *Clr* subset in the *Checked* configuration with the cross compilation option.
 
 You might also want to interact with the container directly for a myriad of reasons, like running multiple builds in different paths for example. In this case, instead of passing the build script command to the `docker` command-line, pass the flag `-it`. When you do this, you will get access to a small shell within the container, which allows you to explore it, run builds manually, and so on, like you would on a regular terminal in your machine. Note that the containers' shell's built-in tools are very limited in comparison to the ones you probably have on your machine, so don't expect to be able to do full work there.

eng/native/configurecompiler.cmake

@@ -540,9 +540,14 @@ if (CLR_CMAKE_HOST_UNIX OR CLR_CMAKE_HOST_WASI)
   # Disable frame pointer optimizations so profilers can get better call stacks
   add_compile_options(-fno-omit-frame-pointer)
 
-  # Make signed arithmetic overflow of addition, subtraction, and multiplication wrap around
+  # Make signed overflow well-defined. Implies the following flags in clang-20 and above.
+  # -fwrapv - Make signed arithmetic overflow of addition, subtraction, and multiplication wrap around
   # using twos-complement representation (this is normally undefined according to the C++ spec).
-  add_compile_options(-fwrapv)
+  # -fwrapv-pointer - The same as -fwrapv but for pointers.
+  add_compile_options(-fno-strict-overflow)
+
+  # Suppress C++ strict aliasing rules. This matches our use of MSVC.
+  add_compile_options(-fno-strict-aliasing)
 
   if(CLR_CMAKE_HOST_APPLE)
     # Clang will by default emit objc_msgSend stubs in Xcode 14, which ld from earlier Xcodes doesn't understand.

eng/pipelines/common/templates/pipeline-with-resources.yml

@@ -17,49 +17,49 @@ extends:
 
     containers:
       linux_arm:
-        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-arm
+        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-arm
         env:
           ROOTFS_DIR: /crossrootfs/arm
 
       linux_arm64:
-        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-arm64
+        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-arm64
         env:
           ROOTFS_DIR: /crossrootfs/arm64
 
       linux_musl_x64:
-        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-amd64-musl
+        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64-musl
         env:
           ROOTFS_DIR: /crossrootfs/x64
 
       linux_musl_arm:
-        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-arm-musl
+        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-arm-musl
         env:
           ROOTFS_DIR: /crossrootfs/arm
 
       linux_musl_arm64:
-        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-arm64-musl
+        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-arm64-musl
         env:
           ROOTFS_DIR: /crossrootfs/arm64
 
       # This container contains all required toolsets to build for Android and for Linux with bionic libc.
       android:
-        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-android-amd64
+        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-android-amd64
 
       # This container contains all required toolsets to build for Android and for Linux with bionic libc and a special layout of OpenSSL.
       linux_bionic:
-        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-android-openssl-amd64
+        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-android-openssl-amd64
 
       # This container contains all required toolsets to build for Android as well as tooling to build docker images.
       android_docker:
-        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-android-docker-amd64
+        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-android-docker-amd64
 
       linux_x64:
-        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-amd64
+        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64
         env:
           ROOTFS_DIR: /crossrootfs/x64
 
       linux_x86:
-        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-x86
+        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-x86
         env:
           ROOTFS_DIR: /crossrootfs/x86
 
@@ -70,7 +70,7 @@ extends:
         image: mcr.microsoft.com/dotnet-buildtools/prereqs:alpine-3.22-amd64
 
       linux_x64_sanitizer:
-        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-amd64-sanitizer
+        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64-sanitizer
         env:
           ROOTFS_DIR: /crossrootfs/x64
 
@@ -83,22 +83,22 @@ extends:
         image: mcr.microsoft.com/dotnet-buildtools/prereqs:almalinux-9-source-build-amd64
 
       linux_s390x:
-        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-s390x
+        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-s390x
         env:
           ROOTFS_DIR: /crossrootfs/s390x
 
       linux_ppc64le:
-        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-ppc64le
+        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-ppc64le
         env:
           ROOTFS_DIR: /crossrootfs/ppc64le
 
       linux_riscv64:
-        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-riscv64
+        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-riscv64
         env:
           ROOTFS_DIR: /crossrootfs/riscv64
 
       linux_loongarch64:
-        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-loongarch64
+        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-loongarch64
         env:
           ROOTFS_DIR: /crossrootfs/loongarch64
 
@@ -109,17 +109,17 @@ extends:
         image: mcr.microsoft.com/dotnet-buildtools/prereqs:centos-stream-10-amd64
 
       browser_wasm:
-        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-webassembly-amd64
+        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-webassembly-amd64
         env:
           ROOTFS_DIR: /crossrootfs/x64
 
       wasi_wasm:
-        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-webassembly-amd64
+        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-webassembly-amd64
         env:
           ROOTFS_DIR: /crossrootfs/x64
 
       freebsd_x64:
-        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net10.0-cross-freebsd-14-amd64
+        image: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-freebsd-14-amd64
         env:
           ROOTFS_DIR: /crossrootfs/x64
 

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;

src/native/libs/System.Security.Cryptography.Native/opensslshim.h

@@ -1463,7 +1463,7 @@ extern TYPEOF(OPENSSL_gmtime)* OPENSSL_gmtime_ptr;
 #define sk_X509_push(stack,value) OPENSSL_sk_push((OPENSSL_STACK*)(1 ? stack : (STACK_OF(X509)*)0), (const void*)(1 ? value : (X509*)0))
 
 // type-safe OPENSSL_sk_pop
-#define sk_X509_pop(stack) OPENSSL_sk_pop((OPENSSL_STACK*)(1 ? stack : (STACK_OF(X509)*)0))
+#define sk_X509_pop(stack) ((X509*)OPENSSL_sk_pop((OPENSSL_STACK*)(1 ? stack : (STACK_OF(X509)*)0)))
 
 // type-safe OPENSSL_sk_pop_free
 #define sk_X509_pop_free(stack, freefunc) OPENSSL_sk_pop_free((OPENSSL_STACK*)(1 ? stack : (STACK_OF(X509)*)0), (OPENSSL_sk_freefunc)(1 ? freefunc : (sk_X509_freefunc)0))

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
                 {