lkml.org 
[lkml]   [2015]   [Apr]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [V6,1/9] elf: Add new powerpc specifc core note sections
On 04/13/2015 02:18 PM, Anshuman Khandual wrote:
> On 04/10/2015 04:03 PM, Ulrich Weigand wrote:
>> Anshuman Khandual <khandual@linux.vnet.ibm.com> wrote on 10.04.2015
>> 11:10:35:
>
> I believed it stores the check pointed MSR value which was in the register
> before the transaction started. But then how it is different from the
> ckpt_regs.msr, I am not sure. Mikey or Michael should be able to clarify
> more on this. I can see "orig_msr" getting used in many places to hold the
> check pointed value of MSR.

tm_orig_msr is used during process context switch only. ckpt_regs
gets used in the signal context where we save all userspace context.
So ptrace would look into the saved MSR value correctly inside
ckpt_regs.msr slot. I believe thats the check pointed MSR value
we are interested in from the ptrace perspective not the tm_orig_msr
which just gets used during process context switch.


>> I may be misreading kernel code, but it seems the kernel does not
>> actually
>> use the ckpt_regs.msr slot at all, and therefore the corresponding slot
>> of
>> the NT_PPC_TM_CGPR regset is likewise undefined/unused. Would it not be
>> more consistent to use that slot to pass the checkpointed MSR?
>
> Hmm. Its a valid point. Would like to get some more clarity on this from
> Mikey whether that slot can be used for check pointed MSR value or not.
> Then why did we have these two slots to hold the same check pointed MSR
> value in the first place at all. Getting confused a bit.

Using ckpt_regs.msr during process context switch instead of tm_orig_msr seems
to be working fine and all the basic TM tests pass, in which case we can drop
tm_orig_msr from thread_struct. Will post a patch on this and see whats the
response from others.



\
 
 \ /
  Last update: 2015-04-20 09:21    [W:0.224 / U:0.704 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site