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Re: [PATCH 5/9] i386: Add address spaces for fs/gs segments
- From: Paolo Bonzini <bonzini at gnu dot org>
- To: Richard Henderson <rth at redhat dot com>, gcc-patches at gcc dot gnu dot org, Avi Kivity <avi dot kivity at gmail dot com>
- Date: Fri, 16 Oct 2015 17:28:31 +0200
- Subject: Re: [PATCH 5/9] i386: Add address spaces for fs/gs segments
- Authentication-results: sourceware.org; auth=none
- References: <1444280375-20866-1-git-send-email-rth at redhat dot com> <1444280375-20866-6-git-send-email-rth at redhat dot com>
On 08/10/2015 06:59, Richard Henderson wrote:
> +/* Address space support.
> +
> + This is not "far pointers" in the 16-bit sense, but an easy way
> + to use %fs and %gs segment prefixes. Therefore:
> +
> + (a) All address spaces have the same modes,
> + (b) All address spaces have the same addresss forms,
> + (c) While %fs and %gs are technically subsets of the generic
> + address space, they are probably not subsets of each other.
> + (d) Since we have no access to the segment base register values
> + without resorting to a system call, we cannot convert a
> + non-default address space to a default address space.
> + Therefore we do not claim %fs or %gs are subsets of generic.
rdfsbase and rdgsbase are potentially accessible to userspace too, so I
think %fs or %gs should be considered subsets of generic.
Paolo
> + Therefore, we need not override any of the address space hooks. */