Messages in this thread | | | Date | Wed, 11 Aug 2010 21:22:51 -0700 | From | "H. Peter Anvin" <> | Subject | Re: + drivers-acpi-apei-erst-dbgc-get_useru64-doesnt-work-on-i386.patch added to -mm tree |
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[Adding Linux and linux-arch. The context is that get_user/put_user don't work on 64 bit values on i386.]
On 08/11/2010 05:33 PM, Andrew Morton wrote: > > Anyway, this should be fixed in x86 core, I suspect.
After looking at it -- and suffering a bad case of déjà vu -- I'm reluctant to change it, as get/put_user are specified to work only on locally atomic data:
* This macro copies a single simple variable from user space to kernel * space. It supports simple types like char and int, but not larger * data types like structures or arrays.
Given that u64 is not a simple type on 32 bits, it would appear that the behavior is intentional.
A user might very well find that supporting u64 and/or structure types would be beneficial, but it would a) be a semantic change, and b) would introduce the possibility of a partially completed transfer. That is a semantic change to the interface. However, it may very well be nicer to have a generally available get_user()/put_user() for the cases which would just kick an EFAULT up the stack when they fail anyway.
If there is consensus for making get_user/put_user a general interface, I'm more than willing to do the x86 changes, but I don't want to do them a) unilaterally and b) for 2.6.36. This seems like .37 material at this point.
-hpa
-- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf.
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