On 2019-01-22 18:00:23 [+0100], Borislav Petkov wrote: > On Tue, Jan 22, 2019 at 05:15:51PM +0100, Oleg Nesterov wrote: > > I don't know... tried to google, found nothing. > > > > the comment in /usr/include/sys/ucontext.h mentions SysV/i386 ABI + historical > > reasons, this didn't help. > > So I'm being told by one of the psABI folks that this is not really > written down somewhere explicitly but it is the result from the POSIX > and psABI treatise of signal handlers, what they're supposed to do, > caller- and callee-saved registers, etc. > > And FPU registers are volatile, i.e., caller-saved. Which means, the > handler itself doesn't save them but the caller, which, doesn't really > expect any signals - they are async. So the kernel must do that and > slap the FPU regs onto the user stack... My point was save them somewhere else if it is possible. So we could save a few cycles during signal delivery and it would make the code a little simpler. Let me finish the series and then we can think how we could improve it. > Hohumm. Makes sense. > Sebastian
