On Mon, Nov 02, 2020 at 07:34:30PM +0100, Borislav Petkov wrote: > On Mon, Nov 02, 2020 at 12:10:00PM -0600, Segher Boessenkool wrote: > > (It does not allow *all* memory and *all* constants, btw... And the > > condition for registers is not really "general register", whatever that > > means... > > I think that means general purpose registers. I.e., it won't use, say > FPU, XMM or whatever special regs. > > What does the asm() parsing code in gcc do for "g"? There should be > some logic which constraints what register is valid...
It just asks the general_operand function, which (for registers) accepts the hard registers that are accessible. This does include the float and vector etc. registers, normally. But you usually have a pseudo-register there (which is always allowed here), unless you used some register asm variable. And pseudos usually are allocated a simple integer register during register allocation, in an asm that is. > > I hope no one ever told you our documentation does not have white > > lies!) > > I have convinced myself of this a couple of times already so I either go > ask our gcc friends or go look straight at gcc source. It is useful to > know folks which hack on it so that I can ask them stupid questions and > not go off into the weeds, trying to figure out what the documentation > says. > > But hey, if that gets the documentation improved, that's a win-win > situation right there. Yes :-) > Might even make people copying from bad examples > to go look at the docs first... Optimism is cool :-) Segher
