Le 26/04/2023 à 14:29, Michael Ellerman a écrit : > Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> writes: >> On Tue, Apr 25, 2023 at 6:58 AM Zhouyi Zhou <zhouzhouyi@xxxxxxxxx> wrote: > ... >> >> Out of curiosity for PPC folks, why cannot 64-bit PPC use per-task >> canary? Michael, is this an optimization? Adding Christophe as well >> since it came in a few years ago via the following commit: > > I think Christophe also answered these in his reply. > > We do use a per-task canary, but because we don't have "current" in a > register, we can't use the value in current for GCC. > > In one of my replies I said a possible solution would be to keep current > in a register on 64-bit, but we'd need to do that in addition to the > paca, so that would consume another GPR which we'd need to think hard > about. An analysis was done here https://github.com/linuxppc/issues/issues/45 showing that r14 is very little used. > > There's another reason to have it in the paca, which is that the paca is > always accessible, even when the MMU is off, whereas current isn't (in > some situations). Even now that powerpc is converted to CONFIG_THREAD_INFO_IN_TASK ? Christophe
