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

Hi Jan,

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).

So obviously, this is not only a MISRA "problem" as you state here and below.

I believe Stefano, Stewart and I provided plenty of documentation/thread to support our positions. Can you provide us documentation/thread showing the compiler will not try to leverage that case?


[1] https://kristerw.blogspot.com/2016/12/pointer-comparison-invalid-optimization.html?m=1

Julien Grall

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