Fix build issue with clang18 (#4730)

Clang 18 introduced some changes that prevent building CoreCLR:

* The warning for VLAs being a C++ extension is now on by default which
causes errors with ```-Werror```.
https://github.com/llvm/llvm-project/issues/62836
* ```stdarg.h``` now has a guard that depends on ```va_arg``` not being
defined, currently the PAL internal doesn't undefined that macro
(despite PAL defining it) which prevent ```stdarg.h``` from being
included again and causes missing symbols (```va_start```, ```va_end```,
```va_arg```).

This PR fixes the warning by disabling it to match the behaviour of
previous clang versions and undefines ```va_arg``` in
```palinternal.h```.

Related PR : https://github.com/dotnet/runtime/pull/94782

diff --git a/eng/native/configurecompiler.cmake b/eng/native/configurecompiler.cmake
index bd80c5c16f4ac02bd26405de94c4102c28a0efa2..df012111d964069f9ebd9f09fee6f63e16818ff6 100644 (file)
--- a/eng/native/configurecompiler.cmake
+++ b/eng/native/configurecompiler.cmake
@@ -549,6 +549,11 @@ if (CLR_CMAKE_HOST_UNIX)
     add_compile_options(-Wimplicit-fallthrough)
   endif()
 
+  # VLAs are non standard in C++, aren't available on Windows and
+  # are a warning by default since clang 18.
+  # For consistency, enable warnings for all compiler versions.
+  add_compile_options($<$<COMPILE_LANGUAGE:CXX>:-Wvla>)
+
   #These seem to indicate real issues
   add_compile_options($<$<COMPILE_LANGUAGE:CXX>:-Wno-invalid-offsetof>)
 
@@ -591,6 +596,9 @@ if (CLR_CMAKE_HOST_UNIX)
     # other clang 16.0 suppressions
     add_compile_options(-Wno-single-bit-bitfield-constant-conversion)
     add_compile_options(-Wno-cast-function-type-strict)
+
+    # clang 18.1 supressions
+    add_compile_options(-Wno-switch-default)
   else()
     add_compile_options(-Wno-uninitialized)
     add_compile_options(-Wno-strict-aliasing)

diff --git a/src/shared/minipal/getexepath.h b/src/shared/minipal/getexepath.h
index a5e12e08a25a006ba4125c4e0f486d1ea7afb959..3c9ad5368ac422f45b27103b7e7fd2fbefee8346 100644 (file)
--- a/src/shared/minipal/getexepath.h
+++ b/src/shared/minipal/getexepath.h
@@ -37,7 +37,7 @@ static inline char* minipal_getexepath(void)
         return NULL;
     }
 
-    char path_buf[path_length];
+    char* path_buf = (char*)alloca(path_length);
     if (_NSGetExecutablePath(path_buf, &path_length) != 0)
     {
         errno = EINVAL;

diff --git a/src/shared/pal/src/file/path.cpp b/src/shared/pal/src/file/path.cpp
index edc9c6c0a6619bbbed9b2b9da097148ba68a88aa..469756e6ce65609e155b13177c3006bd5ec7b6d0 100644 (file)
--- a/src/shared/pal/src/file/path.cpp
+++ b/src/shared/pal/src/file/path.cpp
@@ -401,8 +401,8 @@ GetTempPathW(
         return 0;
     }
 
-    char TempBuffer[nBufferLength > 0 ? nBufferLength : 1];
-    DWORD dwRetVal = GetTempPathA( nBufferLength, TempBuffer );
+    char* tempBuffer = (char*)alloca(nBufferLength > 0 ? nBufferLength : 1);
+    DWORD dwRetVal = GetTempPathA( nBufferLength, tempBuffer );
 
     if ( dwRetVal >= nBufferLength )
     {
@@ -413,7 +413,7 @@ GetTempPathW(
     else if ( dwRetVal != 0 )
     {
         /* Convert to wide. */
-        if ( 0 == MultiByteToWideChar( CP_ACP, 0, TempBuffer, -1,
+        if ( 0 == MultiByteToWideChar( CP_ACP, 0, tempBuffer, -1,
                                        lpBuffer, dwRetVal + 1 ) )
         {
             ASSERT( "An error occurred while converting the string to wide.\n" );

diff --git a/src/shared/pal/src/include/pal/palinternal.h b/src/shared/pal/src/include/pal/palinternal.h
index 15f60cd131a234257a49bc804914042eac8406cd..d7da7ef7c42cdebb0dbaeac8407c37eb1d055d3c 100644 (file)
--- a/src/shared/pal/src/include/pal/palinternal.h
+++ b/src/shared/pal/src/include/pal/palinternal.h
@@ -431,6 +431,7 @@ function_name() to call the system's implementation
 #undef va_start
 #undef va_end
 #undef va_copy
+#undef va_arg
 #undef stdin
 #undef stdout
 #undef stderr