Am 21.11.2013 23:32, schrieb Linus Torvalds:
On Thu, Nov 21, 2013 at 8:02 AM, Alexander Holler <[email protected]> wrote:
The bug is not that gcc can re-order or combine the accesses to "sp".
WE WANT THAT TO HAPPEN.
Sure, and I don't disagree on that.
The bug is *outside* that "current_thread_info()" macro/inline
function. It's the *dereference* of the pointer that gcc re-orders.
AND THAT IS WRONG.
Gcc seems to mess up the alias analysis, and decide that the
deferences cannot alias. Which is wrong. They clearly *can* alias,
exactly because the value of "sp & ~(THREAD_SIZE - 1)" ends up having
the same value all the time.
Sorry, that I still disagree.
I try to describe it more clearly why I still think that the problem
might be because of that const declaration.
(...)
foobar1 = current_thread_info() __attribute_const__ {
return sp->somewhere_local;
}
(...)
foobar2 = current_thread_info() __attribute_const__ {
return sp->somewhere_local;
}
So, even if sp is the same in both cases, that const states that
wherever sp points to is local to current_thread_info(), so it can't be
the same for both cases.
Regards,
Alexander Holler
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