On Mon, Apr 10, 2023 at 10:04 PM Samuel Thibault <samuel.thiba...@gnu.org> wrote: > Sergey Bugaev, le lun. 03 avril 2023 14:56:21 +0300, a ecrit: > > @@ -110,6 +132,10 @@ _hurd_setup_sighandler (struct hurd_sigstate *ss, > > const struct sigaction *action > > ucontext_t *uctxp; /* Points to uctx, below. */ > > } posix; > > }; > > + > > +#ifdef __x86_64__ > > + void *_pad; > > +#endif > > Please mention what that is for.
This is to make sigreturn_addr 16-byte aligned (and this is verified by the static assert below). Our %rsp points right here at &sigreturn_addr when we call the user's signal handler (and then sigreturn, except we ret to it instead of call'ing it, but either way it's pushing or popping 8 bytes), and it needs to be 16-byte aligned before a function call per the x86_64 ABI. You're right that another comment next to _pad itself wouldn't hurt. Sergey
