On Fri, 7 Feb 2025 at 21:51, Rik van Riel <riel@xxxxxxxxxxx> wrote: > > On Fri, 2025-02-07 at 17:03 +0100, Brendan Jackman wrote: > > O > > With !CPU_SUP_AMD and the above, broadcast_kernel_range_flush > > disappears from tlb.o. (Caveat - I didn't actually read the disasm I > > just made it noinline and checked the call disappeared). > > > > It's actually more lines of code but now they're off in a boilerplate > > header and it's consistent with the other flags that do this. > > > What compiler did you use? > > While I like the cleanup in principle, I > don't want to saddle people with older > compilers with extra code they don't need. I used a pretty fresh Clang but I'd be very surprised if it needs a fancy compiler. Compared to if (IS_ENABLED(CONFIG_FOO)) I think all we have with the disabled-features.h magic is - An extra __builtin_constant_p - I did a quick search and I can find GCC release notes referring to this at least back to 4.7 (2012) [0]. Note also this doesn't create any code. - An extra bit of constant folding to turn the (x & y) into true/false. This seems like something compilers have been good at for a long time. And if someone's happy with a compiler so old that it can't do this, I dunno but they probably don't mind a few extra instructions. [1] https://gcc.gnu.org/gcc-4.7/changes.html
