https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96594
Jakub Jelinek <jakub at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Resolution|--- |INVALID Status|UNCONFIRMED |RESOLVED CC| |jakub at gcc dot gnu.org --- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> --- That is just a user error, you didn't read the XChangeProperty man page. "If the specified format is 16, the property data must be a short array. If the specified format is 32, the property data must be a long array." You are using 32, and I assume you are doing this on 64-bit s390x, i.e. where long is 64-bit, so while it sounds weird, libX11 requires you to put the property into a long or unsigned long variable and pass address of that (and read it through that too). It kind of "works" on x86_64, because it is little-endian, so you just have random bits in the upper 32 bits of the long that the library actually reads and perhaps it casts it to a 32-bit type later on. But s390x is big endian, so if you call it with address of a 32-bit variable, the low 32 bits of that are the 32 bits after your variable and can contain arbitrary random values.