Building the native VM with a recent compiler (GCC 16)

[user-0xcafe]

I wanted to build the project locally and faced a compiler error both on master and on the native-final tag. The solution? Adding CFLAGS=-Wno-error=incompatible-pointer-types in front of the sh build.sh invocation.

Error for reference:

[ 32%] Building C object libs/iovm/CMakeFiles/iovmall.dir/source/IoList.c.o
In file included from /home/user/repos/io/libs/iovm/source/IoState.h:269,
                 from /home/user/repos/io/libs/iovm/source/IoObject_inline.h:12,
                 from /home/user/repos/io/libs/iovm/source/IoObject.h:261,
                 from /home/user/repos/io/libs/iovm/source/IoDate.h:9,
                 from /home/user/repos/io/libs/iovm/source/IoFile.c:17:
/home/user/repos/io/libs/iovm/source/IoFile.c: In function ‘IoFile_readUArrayOfLength_’:
/home/user/repos/io/libs/iovm/source/IoState_inline.h:24:29: error: returning ‘IoObject *’ {aka ‘struct CollectorMarker *’} from a function with incompatible return type ‘UArray *’ [-Wincompatible-pointer-types]
   24 | #define IONIL(self) (IOSTATE->ioNil)
      |                     ~~~~~~~~^~~~~~~~
/home/user/repos/io/libs/iovm/source/IoFile.c:815:38: note: in expansion of macro ‘IONIL’
  815 |     if (IOSTATE->errorRaised) return IONIL(self);
      |                                      ^~~~~

[stevedekorte]

Thanks for the report and the workaround. There was a genuine bug behind the warning: IoFile_readUArrayOfLength_ (libs/iovm/source/IoFile.c) returns UArray *, but its error path returned IONIL(self) — which is an IoObject *. GCC 16 now treats that incompatible-pointer return as an error by default.

It was also a latent logic/leak bug, since both callers test the result for NULL to decide whether to return Nil; the non-NULL ioNil pointer made a failed read look successful, and the freshly allocated buffer leaked.

Fixed in #499 (merged to master, and cherry-picked to the native, stackless, and wasm branches) by freeing the buffer and returning NULL. After updating you should be able to build with GCC 16 without the -Wno-error=incompatible-pointer-types flag.