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Re: [MirageOS-devel] unsigned integers

  • To: Hannes Mehnert <hannes@xxxxxxxxxxx>
  • From: Anil Madhavapeddy <anil@xxxxxxxxxx>
  • Date: Wed, 7 Sep 2016 15:26:28 +0100
  • Cc: "mirageos-devel@xxxxxxxxxxxxxxxxxxxx" <mirageos-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Wed, 07 Sep 2016 14:26:35 +0000
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On 7 Sep 2016, at 15:21, Hannes Mehnert <hannes@xxxxxxxxxxx> wrote:
> On 07/09/2016 15:08, Anil Madhavapeddy wrote:
>> I'd prefer to allocate and have a good API, but then I would also prefer to 
>> not use compiler builtins that may introduce subtle optimisation bugs in the 
>> future -- or at least until we know that the optimisations are useful.
>> E.g. the double fetch vulnerabilities that emerged from compiler builtins 
>> https://xenbits.xen.org/xsa/advisory-155.html (not directly applicable here, 
>> but my point is that I'd prefer a slightly slower but more consistent first 
>> cut at this library)
> I don't see the relation between builtins and compiler optimisations,
> but I might lack knowledge about the bug.  Looking into some patches,
> such as
> https://xenbits.xen.org/xsa/xsa155-linux43-0005-xen-blkback-read-from-indirect-descriptors-only-once.patch
> it has not much to do with builtins.
> My first cut of this library was to use the builtins, since they're
> available on all platforms I care about, but then Travis CI turned to be
> unhappy (since it seems most Linux distributions ship arcane versions of
> gcc).

Sadly we do have to support GCC3/4 for some time in core libraries (e.g. 
OpenBSD base uses the last GPLv2 version of GCC3 in base)...

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