[release/8.0] va_start/va_end compile time errors with clang 18 + libstdc++ 14

[omajid]

I am trying to build runtime release/8.0 with clang 18 after these changes:

diff --git a/eng/common/native/init-compiler.sh b/eng/common/native/init-compiler.sh
index f5c1ec7eafe..2d5660642b8 100644
--- a/eng/common/native/init-compiler.sh
+++ b/eng/common/native/init-compiler.sh
@@ -63,7 +63,7 @@ if [ -z "$CLR_CC" ]; then
     # Set default versions
     if [ -z "$majorVersion" ]; then
         # note: gcc (all versions) and clang versions higher than 6 do not have minor version in file name, if it is zero.
-        if [ "$compiler" = "clang" ]; then versions="17 16 15 14 13 12 11 10 9 8 7 6.0 5.0 4.0 3.9 3.8 3.7 3.6 3.5"
+        if [ "$compiler" = "clang" ]; then versions="18 17 16 15 14 13 12 11 10 9 8 7 6.0 5.0 4.0 3.9 3.8 3.7 3.6 3.5"
         elif [ "$compiler" = "gcc" ]; then versions="13 12 11 10 9 8 7 6 5 4.9"; fi
 
         for version in $versions; do
diff --git a/eng/native/configurecompiler.cmake b/eng/native/configurecompiler.cmake
index 18381101853..0e6ee88b245 100644
--- a/eng/native/configurecompiler.cmake
+++ b/eng/native/configurecompiler.cmake
@@ -590,6 +590,9 @@ 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)

However, this fails with the following errors:

  /home/omajid/runtime/src/coreclr/pal/src/cruntime/filecrt.cpp:89:9: error: use of undeclared identifier 'va_start'
     89 |         va_start(ap, nFlags);
        |         ^
  /home/omajid/runtime/src/coreclr/pal/src/cruntime/filecrt.cpp:91:9: error: use of undeclared identifier 'va_end'
     91 |         va_end(ap);
        |         ^
  /home/omajid/runtime/src/coreclr/pal/src/cruntime/filecrt.cpp:126:9: error: use of undeclared identifier 'va_start'
    126 |         va_start(ap, nFlags);
        |         ^
  /home/omajid/runtime/src/coreclr/pal/src/cruntime/filecrt.cpp:128:9: error: use of undeclared identifier 'va_end'
    128 |         va_end(ap);
        |         ^
  4 errors generated.

Taking a page from pal/src/cruntime/misc.cpp and making this change to the files that show the error does not help:

diff --git a/src/coreclr/pal/src/cruntime/printfcpp.cpp b/src/coreclr/pal/src/cruntime/printfcpp.cpp
index b9c1c92b9bc..e5f715fa419 100644
--- a/src/coreclr/pal/src/cruntime/printfcpp.cpp
+++ b/src/coreclr/pal/src/cruntime/printfcpp.cpp
@@ -29,6 +29,9 @@ Revision History:
 #include "pal/cruntime.h"
 
 #include <errno.h>
+/* <stdarg.h> needs to be included after "palinternal.h" to avoid name
+   collision for va_start and va_end */
+#include <stdarg.h>
 
 SET_DEFAULT_DEBUG_CHANNEL(CRT);
 

[omajid]

Any idea how to debug this, @janvorli ?

[janvorli]

@omajid, cmake generated makefiles can be used to produce preprocessed file for any compiled source (a file that contains all the includes inlined and all defines handled). That is usually useful to figure out why some symbol is not visible at some point.
So for your case, you'd do (the stuff below assuming debug build, but it works for any)

cd artifacts/obj/coreclr/linux.x64.Debug/pal/src
make cruntime/filecrt.cpp.i

[janvorli]

It will print out a relative path to the produced file

[mateusrodrigues]

I did the steps described above in two different environments (clang17 and clang18):

clang17:

    ...
    if (nFlags & 0100)
    {
        __builtin_va_start(ap, nFlags);
        mode = __builtin_va_arg(ap, int);
        __builtin_va_end(ap);
    }
    ...

clang18:

    ...
    if (nFlags & 0100)
    {
        va_start(ap, nFlags);
        mode = __builtin_va_arg(ap, int);
        va_end(ap);
    }
    ...

Notice how va_arg gets handled to __builtin_va_arg, but va_start and va_end remain on clang18.

[mateusrodrigues]

@omajid looks like a fix has already been commited to main and made it to 9.0: #94782

This probably needs backporting to release/8.0?

[omajid]

Thank you! I opened #100258

[omajid]

Fixed by #100258