Re: [Xen-devel] RFC: 32 bits as smallest atomic size.

[Jimi Xenidis <jimix@xxxxxxxxxxxxxx>]

>>>>> "KF" == Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> writes:

 KF> On 26 Mar 2005, at 17:49, Keir Fraser wrote:

 KF> Actually, one of the more interesting thing to discuss imo is how to 
 KF> structure the public interface headers to support multiple 
 KF> architectures. Is it feasible to strive for much commonality, or should 
 KF> each arch have its own public headers, or what? I don't have a good 
 KF> feel for what the best solution is going to be...

Considering that on PPC we'll be trying to support domains of several
different ABIs (ELF, XCOFF and MachO) not to mention 32 bit apps on
64bit machines, we are extremely sensitive (and sympathetic) to your
goals.

On x86 you have Windows, and their (intentionally) incompatible 64 bit
ABI :(

The current use of specific sized types is good for this goal.
Typically, defining these data structures with a member order that
removes padding, or padding explicitly to disambiguate structure
layout, is a good strategy (-Wpadded can help here).

I think we will disable PACKED on PPC and see how that goes, as we
detect padded areas we will submit patches that may shuffle structure
members to achieve the above goals.

WRT to subword accesses, we will continue to eveluate them and
generate some patches for your approval, rather than attempt to
shuffle bits around at runtime.

-JX


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