Build error with gcc: `ivar.h:85:1: error: enumerator value for 'ivar_align_mask' is not an integer constant`

[barracuda156]

[ 25%] Building C object CMakeFiles/objc.dir/encoding2.c.o
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/opt/local/bin/ccache /opt/local/bin/gcc-mp-14 -DCXA_ALLOCATE_EXCEPTION_SPECIFIER -DEMBEDDED_BLOCKS_RUNTIME -DGNUSTEP -DOLDABI_COMPAT=1 -DTYPE_DEPENDENT_DISPATCH -D__OBJC_BOOL -D__OBJC_RUNTIME_INTERNAL__=1 -Dobjc_EXPORTS -I/opt/local/include -I/opt/local/var/macports/build/libobjc2-f1652def/work/build/objc -pipe -Os -DNDEBUG -I/opt/local/include -isysroot/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk -arch x86_64 -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk -mmacosx-version-min=10.15 -fPIC -fexceptions -Wno-gnu-folding-constant -MD -MT CMakeFiles/objc.dir/alias_table.c.o -MF CMakeFiles/objc.dir/alias_table.c.o.d -o CMakeFiles/objc.dir/alias_table.c.o -c /opt/local/var/macports/build/libobjc2-f1652def/work/libobjc2-2.3/alias_table.c
In file included from /opt/local/var/macports/build/libobjc2-f1652def/work/libobjc2-2.3/legacy.h:3,
                 from /opt/local/var/macports/build/libobjc2-f1652def/work/libobjc2-2.3/class_table.c:10:
/opt/local/var/macports/build/libobjc2-f1652def/work/libobjc2-2.3/ivar.h:85:1: error: enumerator value for 'ivar_align_mask' is not an integer constant
   85 | } objc_ivar_flags;
      | ^
cc1: note: unrecognized command-line option '-Wno-gnu-folding-constant' may have been intended to silence earlier diagnostics
make[2]: *** [CMakeFiles/objc.dir/class_table.c.o] Error 1
make[2]: *** Waiting for unfinished jobs....
/opt/local/var/macports/build/libobjc2-f1652def/work/libobjc2-2.3/builtin_classes.c:106:1: internal compiler error: in machopic_select_section, at config/darwin.cc:1828
  106 | }
      | ^
Please submit a full bug report, with preprocessed source (by using -freport-bug).
See <https://github.com/macos-powerpc/powerpc-ports/issues/new> for instructions.
<stdin>:61:1: error: assembler local symbol 'L_OBJC_CLASS_Protocol' not defined

^
<stdin>:61:1: error: assembler local symbol 'L_OBJC_CLASS_ProtocolGSv1' not defined

^
<stdin>:61:1: error: assembler local symbol 'L_OBJC_CLASS_Object' not defined

^
<stdin>:61:1: error: assembler local symbol 'L_OBJC_CLASS_ProtocolGCC' not defined

^
<stdin>:61:1: error: assembler local symbol 'L_OBJC_CLASS___IncompleteProtocol' not defined

^
<stdin>:61:1: error: assembler local symbol 'L_OBJC_CLASS__ObjC_Protocol_Holder_Ugly_Hack' not defined

^
make[2]: *** [CMakeFiles/objc.dir/builtin_classes.c.o] Error 1

Possibly related: #329

[davidchisnall]

It looks as if you’re building with GCC? That isn’t really supported, GCC’s Objective-C support is largely vestigial and it doesn’t support vaguely modern features or the newer ABIs.

[barracuda156]

@davidchisnall From README it follows that older ObjC ABI should be automatically picked with gcc:

libobjc2/README.md

Lines 11 to 13 in e5c06e3

	- The old GCC ABI, which provides support for Objective-C 1.0 features. This
	can be selected via the `-fobjc-runtime=gcc` flag in Clang or by compiling
	with GCC.