Messages in this thread | | | Date | Mon, 11 May 2015 13:53:40 +0200 | From | Laurent Dufour <> | Subject | Re: powerpc: Enabling sys_kcmp for CRIU |
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On 11/05/2015 12:31, Michael Ellerman wrote: > On Tue, 2015-05-05 at 15:30:21 UTC, Laurent Dufour wrote: >> The commit 8170a83f15ee ("powerpc: Wireup the kcmp syscall to sys_ni") has >> disabled the kcmp syscall for powerpc. This has been done due to the use >> of unsigned long parameters which may require a dedicated wrapper to handle >> 32bit process on top of 64bit kernel. However in the kcmp() case, the 2 >> unsigned long parameters are currently only used to carry file descriptors >> from user space to the kernel. Since such a parameter is passed through >> register, and file descriptor doesn't need to get extended, there is, >> today, no need for a wrapper. >> >> In the case there will be a need to pass address in or out of this system >> call, then a wrapper could be required, it will then be to care of it. >> >> As today this is not the case, it is safe to enable kcmp() on powerpc. > > That's mostly convincing. Though I see that s390 does have a compat wrapper, > i386 doesn't. So who knows what that means. > > But, there's a selftest in tools/testing/selftests/kcmp. So can you run that as > 32-bit and confirm it works? Then I'd be 100% convinced :)
Hi Michael,
I was myself a bit confused about this system call, so to be sure before sending the patch I ran the selftest/kcmp series on 64bit, 32bit, and also build it in 32bit and run it on top of a 64bit kernel without any trouble...
Cheers, Laurent.
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