Re: [PATCH v8 08/10] x86, mpx: add prctl commands PR_MPX_REGISTER, PR_MPX_UNREGISTER

[Dave Hansen]

On 09/15/2014 08:20 PM, Ren, Qiaowei wrote:
>> What are the semantics across execve() ?
>> 
> This will not impact on the semantics of execve(). One runtime
> library
> for MPX will be provided (or merged into Glibc), and when the
> application starts, this runtime will be called to initialize MPX
> runtime environment, including calling prctl() to notify the kernel to
> start managing the bounds directories. You can see the discussion
> about exec(): https://lkml.org/lkml/2014/1/26/199

I think he's asking what happens to the kernel value at execve() time.

The short answer is that it is zero'd along with the rest of a new mm.
It probably _shouldn't_ be, though.  It's actually valid to have a bound
directory at 0x0.  We probably need to initialize it to -1 instead, and
that means initializing to -1 at execve() time.
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