There are two issues here - first, this macro uses AT&T specific syntax with $, which is not necessary. Also, some assemblers (nasm) emit different bytes for "int 3" and "int3", so it's better to use "int3" (cd 03 vs cc)
More importantly, GDB has some failing assertion whenever stepping after hitting an "int3" instruction. This makes it practically useless, as is. For some reason, putting a nop afterwards as a workaround is okay.
Related discussions:
https://sourceware.org/bugzilla/show_bug.cgi?id=31194https://lists.sr.ht/~skeeto/public-inbox/%3C2d3d7662a361ddd049f7dc65b94cecdd%40disroot.org%3E
