ifdef __linux__ / gtk issue; how to list defined symbols for cmake?

[Jan Beich]

Gary Aitken <freebsd at dreamchaser.org> writes:

> 1.  Is there an easy way to get a list of all the __*__ symbols?

# Works for GCC, Clang and some arcane compilers
$ cc -dM -E -</dev/null

# Clang being a cross-compiler can check other targets
$ clang -target x86_64-apple-darwin18.2.0 -dM -E -</dev/null | fgrep -i -e unix -e apple
#define __APPLE_CC__ 6000
#define __APPLE__ 1
$ clang -target armv7-unknown-freebsd12.0-gnueabihf -dM -E -</dev/null | fgrep -i neon
#define __ARM_NEON 1
#define __ARM_NEON_FP 0x4
#define __ARM_NEON__ 1

>     Where / how are these set up?

Predefined macros are set by the compiler. Some are architecture-specific,
some are OS-specific, some depend on flags, etc.

https://gcc.gnu.org/onlinedocs/cpp/Predefined-Macros.html

For one, __FreeBSD__ is defined in
/usr/src/contrib/llvm/tools/clang/lib/Basic/Targets/OSTargets.h
/usr/src/contrib/gcc/config/freebsd-spec.h

>     Is there a way to list them at the start of compilation of each file
>     to check the appropriate ones are all defined in different subdirs
>     of the build tree?

Unlikely without hacking the build glue to add a separate step for -dM -E.

>     If __linux__ is defined, is __unix__ also defined?  If any of the
>     __*BSD__ syms are defined, is __unix__ also defined?

__unix__ is defined on (m)any Unix-like system except macOS despite macOS
being on of the few certified UNIX. Go figure. ;)

https://sourceforge.net/p/predef/wiki/OperatingSystems/

> 3.  What's the relationship between the _WIN32, __APPLE__, __unix__ type
>     syms in code and the WIN32, APPLE, UNIX, XCODE syms that I see in
>     some of the CMakeLists.txt files?

CMake predefines some variables and even more are defined by cmake-modules(7).
However, UNIX is defined on macOS unlike __unix__. What a rotten apple. ;)

https://github.com/Kitware/CMake/blob/v3.14.5/Source/cmStateSnapshot.cxx#L298-L355
https://github.com/Kitware/CMake/blob/v3.14.5/Source/cmGlobalXCodeGenerator.cxx#L297-L298

>  Are any/all of these case sensitive?

Yep if the underlying programming language is case-sensitive.

>     How is CMAKE_SYSTEM_NAME, which may be "Linux" (on linux), related to
>     the above syms?

See /usr/local/share/cmake/Modules/CMakeDetermineSystem.cmake

>
> 4.  Suggestions on how to approach this?  I'm inclined to change the
>       "#if defined(__linux__)" to "#if defined(__WXGTK__)" where appropriate
>     instead of adding
>       "|| defined(__FreeBSD__) || defined(__NetBSD__)..." etc.

Probably OK but I don't have experience porting WX-based apps. Try to
insert #error first to make sure __WXGTK__ is defined in all the places
you're trying to use it.

>     Is there a "BSD" sym that encompasses the various bsd variants?

AFAIK, "BSD" defined in <sys/param.h> is a vestige from when BSD was an
actual Unix distribution developed by CSRG at UC Berkeley. As macOS and
GNU/kFreeBSD also define "BSD" it's not very useful.

https://svnweb.freebsd.org/csrg?view=revision&revision=24654
http://fxr.watson.org/fxr/source/bsd/sys/param.h?v=xnu-2050.18.24#L72