> > On 01/11/17 12:54, gengdongjiu wrote: > > Hi Robin, > > > > On 2017/11/1 19:24, Robin Murphy wrote: > >>> + esb > >>> +alternative_else_nop_endif > >>> +1: > >>> + .endm > >> Having a branch in here is pretty horrible, and furthermore using > >> label number 1 has a pretty high chance of subtly breaking code where > >> this macro is inserted. > >> > >> Can we not somehow nest or combine the alternative conditions here? > > > > I found it will report error if combine the alternative conditions here. > > > > For example: > > > > + .macro error_synchronize > > +alternative_if ARM64_HAS_IESB > > +alternative_if ARM64_HAS_RAS_EXTN > > + esb > > +alternative_else_nop_endif > > +alternative_else_nop_endif > > + .endm > > > > And even using b.eq/cbz instruction in the alternative instruction in > > arch/arm64/kernel/entry.S, it will report Error. > > > > For example below > > > > alternative_if ARM64_HAS_PAN > > xxxxxxxxxxxxxxxxxxxx > > b.eq xxxxx > > alternative_else_nop_endif > > > > I do not dig it deeply, do you know the reason about it or good suggestion > > about that? > > Thanks a lot in advance. > > Actually, on second look ARM64_HAS_RAS_EXTN doesn't even matter - ESB is a > hint, so if the CPU doesn't have RAS it should behave as a > NOP anyway.
Yes, you are right. It is "HINT #16" So in fact it can be written below: + .macro error_synchronize +alternative_if_not ARM64_HAS_IESB + esb +alternative_else_nop_endif + .endm If written to that, whether it will be strange? although ESB should behave as a NOP anyway if the CPU doesn't have RAS. > > On which note, since I don't see one here - are any of those other patches > defining an "esb" assembly macro similar to the inline asm case? > If not then this isn't going to build with older toolchains - perhaps we > should just use the raw hint syntax directly. Sorry for that I do not push the dependent patch[1]. The "ESB" is defined as a macro /* + * RAS Error Synchronization barrier + */ + .macro esb + hint #16 + .endm + +/* [1] https://www.spinics.net/lists/arm-kernel/msg612884.html > > Robin. _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
