[PATCH] D64597: CodeGet: Init 32bit pointers with 0xFFFFFFFF

Fri Jul 12 09:43:32 PDT 2019

jfb added a comment.

In D64597#1582944 <https://reviews.llvm.org/D64597#1582944>, @hubert.reinterpretcast wrote:

> In D64597#1581605 <https://reviews.llvm.org/D64597#1581605>, @pcc wrote:
>
> > The problem with `0xaaaaaaaa` on 32-bit is that it is likely to be a valid address.
> >
> > When I discussed this with JF I proposed a pointer initialization of `0xffffffff` which he agreed to. This value is very likely to trap when accessed (due to accesses likely wrapping to zero) and also has the benefit of being the same pattern as for floats.
>
>
> The value is very likely not to trap on some systems (due to accesses likely wrapping to zero). I am not sure I have a better magic value to offer though.

On 32-bit platforms the only region that's likely to trap is the zero page. This seems to be the best choice, but platforms with other regions should be able to tune this value (i.e. I'd accept platform checks here which change the value on such a target).

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https://reviews.llvm.org/D64597