Messages in this thread | | | Date | Fri, 22 Nov 2013 00:18:58 +0100 | From | Alexander Holler <> | Subject | Re: current_thread_info() not respecting program order with gcc 4.8.x |
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Am 21.11.2013 23:32, schrieb Linus Torvalds: > On Thu, Nov 21, 2013 at 8:02 AM, Alexander Holler <holler@ahsoftware.de> 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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