On Thu, Mar 23, 2023 at 02:49:34PM +0000, Conor Dooley wrote: > This would requiring picking up your patch Jason, but with an > "if !XIP_KERNEL" added to the select. So the risk of making this all work is that we wind up forgetting to add `select alternatives if !xip` to various places that need it (fpu, kvm, maybe others? future others?), because it appears to work, thanks to the code in your patch. But making it work is also probably a good thing, since we obviously want the fpu and maybe other things to work on xip kernels. So maybe we should get rid of the CONFIG_RISCV_ALTERNATIVES knob entirely, making it "always enabled", and then conditonalize the alternatives code to BUILD_BUG_ON when called with CONFIG_XIP_KERNEL=y. Then, this build bug will get hit immediately by riscv_has_extension_*(), which will then require your patch, which can run in a `if (IS_ENABLED(XIP_KERNEL))` block or similar. The result of that will be: - !xip kernels properly use the fast riscv_has_extension_*() code and any alternatives code needed, since it's always selected. - xip kernels get a BUILD_BUG_ON if they use any alternatives-based code that doesn't have a xip fallback yet. What do you think of that approach? A "lighter weight" version of that approach would be to just remove all of the `select RISCV_ALTERNATIVES` lines, and instead make RISCV_ALTERNATIVES specify `default !XIP_KERNEL`. That would more or less amount to the above too, though with weirder error cases. Jason
