Warning issued on cdefs.h (invoked from stdlib.h) with LLVM18.18 and MacOS15.6.1

[mirkov]

Hello,

first time C2FFI user, and with next to non-existent with C compilation expertise. My issue is on MacOS15.6.1 and LLVM 18.1.8.

I have applied c2ffi to the GNU Scientific Library (GSL): GSL - GNU Scientific Library - GNU Project - Free Software Foundation. I built GSL on my laptop using the standard ./configure, make sequence, using Apple's provided compiler and linker. No issues during the build.

I write to understand whether a warning issued by C2FFI is something to be concerned about. A secondary reason is that even if it is nothing to be concerned about, there is a statement to that effect for other users here, so they don't have to worry about it either.

During processing of each of GSL's files, the following is emitted:

c2ffi warning: Unhandled environment: '' for triple ''
In file included from ../../gsl/gsl-2.8/gsl/gsl_min.h:23:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk/usr/include/stdlib.h:58:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk/usr/include/_stdlib.h:65:
/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk/usr/include/sys/cdefs.h:81:2: warning: "Unsupported compiler detected" [-W#warnings]
   81 | #warning "Unsupported compiler detected"
      |  ^

This originates in the cdefs.h file. I can replicate the warning by applying C2FFI to stdlib.h as well.

Line 81 of cdefs.h contains:

/* This SDK is designed to work with clang and specific versions of
 * gcc >= 4.0 with Apple's patch sets */
#if !defined(__GNUC__) || __GNUC__ < 4
#warning "Unsupported compiler detected"
#endif

GSL has 266 header files, and each includes stdlib.h, thus each generating this warning.

My best guess is that the LLVM and clang I installed via Homebrew (18.1.8) do not pass Apple's GCC test. But that is only a guess.

Thanks for any insights.