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Re: [Xen-devel] [PATCH v6 1/4] xen: introduce SYMBOL



Hi Jan,

On 18/01/2019 11:09, Jan Beulich wrote:
On 18.01.19 at 11:48, <julien.grall@xxxxxxx> wrote:
On 18/01/2019 09:54, Jan Beulich wrote:
On 18.01.19 at 02:24, <sstabellini@xxxxxxxxxx> wrote:
On Thu, 17 Jan 2019, Jan Beulich wrote:
On 17.01.19 at 01:37, <sstabellini@xxxxxxxxxx> wrote:
On Wed, 16 Jan 2019, Jan Beulich wrote:
Stop. No. We very much can prove they are - _end points at
one past the last element of _start[]. It is the compiler which
can't prove the opposite, and hence it can't leverage
undefined behavior for optimization purposes.

You keep saying the compiler can't leverage it for optimization purpose, however
there are confirmations that GCC may actually leverage it (e.g [1]). You
actually need to trick the compiler to avoid the optimization (e.g RELOC_HIDE).

Correct - that's the case I'm referring to when saying it can't leverage
undefined behavior optimizations anymore. Without the hiding of
course it can.

But this trick is GCC specific, right? So we would need to have one trick for each compiler we support. Note that the solution originally suggested by Stefano has the same issue (i.e return unsigned long).

Cheers,

--
Julien Grall

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