[llvm][clang] undeclared identifier 'malloc' and 'free' in runOnNewStack

[kykrueger]

While building main with vcpkg I've come across a bug introduced with #136046

/Users/kykrueger/repos/vcpkg/buildtrees/llvm/src/e0a7de5d9d-142095e5f5.clean/llvm/lib/Support/ProgramStack.cpp:114:17: error: use of undeclared identifier 'malloc'
  114 |   void *Stack = malloc(StackSize);
      |                 ^
/Users/kykrueger/repos/vcpkg/buildtrees/llvm/src/e0a7de5d9d-142095e5f5.clean/llvm/lib/Support/ProgramStack.cpp:119:3: error: use of undeclared identifier 'free'
  119 |   free(Stack);

I'm looking into why malloc and free are not being found.

[kykrueger]

Since this feature seems to be restricted to apple ARM64, I'd like to include that this is failing to build on an M4 Max chip, and only when building with vcpkg, so this might be a configuration problem.

[shafik]

CC @Bigcheese @rjmccall

[kykrueger]

It seems to me that we had been building llvm and mlir with only libc++ and not libc. Yet the flags around the new feature just check if I am running on a Mac with ARM64 silicon instead of the presence of malloc.h.

Then, building on Mac without malloc.h results in this crash.

[kykrueger]

@Bigcheese, would you mind clarifying where you expect the build to find malloc and free in runOnNewStack?
I don't see why we wouldn't want to use llvm::safe_malloc in this case, and when using malloc why cstdlib isn't included in the .cpp file where malloc is called.

[kykrueger]

To get my build working I added an include on cstdlib to the ProgramStack.cpp file when LLVM_HAS_SPLIT_STACKS is defined:

diff --git a/llvm/lib/Support/ProgramStack.cpp b/llvm/lib/Support/ProgramStack.cpp
index 66f74ff660b2..4e2bba6392c7 100644
--- a/llvm/lib/Support/ProgramStack.cpp
+++ b/llvm/lib/Support/ProgramStack.cpp
@@ -20,6 +20,8 @@
 
 #ifndef LLVM_HAS_SPLIT_STACKS
 # include "llvm/Support/thread.h"
+#else 
+# include <cstdlib> // for malloc and free
 #endif
 
 using namespace llvm;

I have not had much time to dig into why the our vcpkg port of llvm is failing without this.

If the vcpkg repos manage to update their latest version maybe they will have included some changes that have fixed this here
microsoft/vcpkg#46825