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

Steven Rostedt
2013-08-05T19:04:33Z

On Mon, 2013-08-05 at 11:34 -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.

I would love to. But IIRC, the asm_goto() has some strict constraints.
We may be able to jump to a different section, but we have no way of
coming back. Not to mention, you must tell the asm goto() what label you
may be jumping to.

I don't know how safe something like this may be:

static inline trace_sched_switch(prev, next)
{
asm goto("jmp foo1\n" : : foo2);
foo1:
return;

asm goto(".pushsection\n"
"section \".foo\"\n");
foo2:
__trace_sched_switch(prev, next);
asm goto("jmp foo1"
".popsection\n" : : foo1);
}

The above looks too fragile for my taste. I'm afraid gcc will move stuff
out of those "asm goto" locations, and make things just fail. But I can
play with this, but I don't like it.

-- Steve