Re: [RFC] gcc feature request: Moving blocks into sections

Jason Baron
2013-08-05T19:58:03Z

On 08/05/2013 03:40 PM, Marek Polacek wrote:
> On Mon, Aug 05, 2013 at 11:34:55AM -0700, Linus Torvalds wrote:
>> On Mon, Aug 5, 2013 at 11:24 AM, Linus Torvalds
>> <torvalds@linux-foundation.org> wrote:
>>> Ugh. I can see the attraction of your section thing for that case, I
>>> just get the feeling that we should be able to do better somehow.
>> Hmm.. Quite frankly, Steven, for your use case I think you actually
>> want the C goto *labels* associated with a section. Which sounds like
>> it might be a cleaner syntax than making it about the basic block
>> anyway.
> FWIW, we also support hot/cold attributes for labels, thus e.g.
>
> if (bar ())
> goto A;
> /* ... */
> A: __attribute__((cold))
> /* ... */
>
> I don't know whether that might be useful for what you want or not though...
>
> Marek
>

It certainly would be.

That was how I wanted to the 'static_key' stuff to work, but
unfortunately the last time I tried it, it didn't move the text
out-of-line any further than it was already doing. Would that be
expected? The change for us, if it worked would be quite simple.
Something like:

--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -21,7 +21,7 @@ static __always_inline bool arch_static_branch(struct
static_key *key)
".popsection \n\t"
: : "i" (key) : : l_yes);
return false;
-l_yes:
+l_yes: __attribute__((cold))
return true;
}