On 28 June 2018 at 11:25, Peter Zijlstra [off-list ref] wrote:

On Thu, Jun 28, 2018 at 11:04:45AM +0200, Ard Biesheuvel wrote:

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On 28 June 2018 at 11:02, Ard Biesheuvel [off-list ref] wrote:

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@@ -56,7 +72,9 @@ jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)

      size = (((unsigned long)stop - (unsigned long)start)
                                      / sizeof(struct jump_entry));
-     sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
+     sort(start, size, sizeof(struct jump_entry), jump_label_cmp,
+          IS_ENABLED(CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE) ? jump_label_swap
+                                                           : NULL);
 }

That will result in jump_label_swap being an unused symbol for some
compile options.

No, and isn't that the point of IS_ENABLED()? The compiler sees a
reference to jump_label_swap(), so it won't complain about it being
unused.

Ah, ok. I hadn't figured it was quite that smart about it.

Yeah. I could use a temp variable to make the indentation less
obnoxious, but since this is an opt-in feature, I'd like to preserve
the NULL (*swap)() argument for the existing users.

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Meh. I thought IS_ENABLED() was preferred over #ifdef, no?

Dunno, I just reacted to the proposed code's uglyness :-)

I will try to come up with something that rhymes, ok? :-)

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... and it means the sort() routine will unconditionally perform an
indirect function call even if the arch does not require it.

Yeah, not sure I care about that here, this is a one time affair, very
far away from any fast paths.

Fair enough.