Matthew -- fine, you collected information. Thank you. It is quite clear that POSIX set in stone an accident, a significant error in my opinion. Anyone with enough expertise can recognize this is an accident in the SVR4 codebase, which ended up being "ratified" (in quotes, because the more mistakes you make, the less value there is). This specific refinement may help a few pieces of code which require specific detail in siginfo, but it introduces a lot more accidental risk in those which only use the signal number/handler.
It is complicated enough that it requires experts to review how (typically poorly) programs (written by non-experts) use signals to deal with this added kernel behaviour. As in, it is bad enough that I am scared even for the way that SIGBUS and SIGSEGV handlers in crap programs in base handle it. The issue of unsafe terminal signal handlers returns IN FORCE, and we need to cope with those. Nothing ever changes, noone ever learns, noone cares. Where we go from continues to be a big question mark. Compatible? one issue.. not compatible? another issue.. Thanks POSIX, whoever you are. What favors did you do us recently?
