linux-kernel - Re: [PATCH V2 2/3] powerpc, ptrace: Enable support for transactional memory register sets

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Message-ID: <53730326.6000400@linux.vnet.ibm.com>
Date:	Wed, 14 May 2014 11:16:14 +0530
From:	Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:	Pedro Alves <palves@...hat.com>
CC:	linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org,
	michael@...erman.id.au, mikey@...ling.org, avagin@...nvz.org,
	oleg@...hat.com
Subject: Re: [PATCH V2 2/3] powerpc, ptrace: Enable support for transactional
 memory register sets

On 05/13/2014 10:43 PM, Pedro Alves wrote:
> On 05/05/14 08:54, Anshuman Khandual wrote:
>> This patch enables get and set of transactional memory related register
>> sets through PTRACE_GETREGSET/PTRACE_SETREGSET interface by implementing
>> four new powerpc specific register sets i.e REGSET_TM_SPR, REGSET_TM_CGPR,
>> REGSET_TM_CFPR, REGSET_CVMX support corresponding to these following new
>> ELF core note types added previously in this regard.
>>
>> 	(1) NT_PPC_TM_SPR
>> 	(2) NT_PPC_TM_CGPR
>> 	(3) NT_PPC_TM_CFPR
>> 	(4) NT_PPC_TM_CVMX
> 
> Sorry that I couldn't tell this from the code, but, what does the
> kernel return when the ptracer requests these registers and the
> program is not in a transaction?  Specifically I'm wondering whether
> this follows the same semantics as the s390 port.
> 

Right now, it still returns the saved state of the registers from thread
struct. I had assumed that the user must know the state of the transaction
before initiating the ptrace request. I guess its better to check for
the transaction status before processing the request. In case if TM is not
active on that thread, we should return -EINVAL.

I am not familiar with the s390 side of code. But if we look at the
s390_tdb_get function it checks for (regs->int_code & 0x200) before
processing the request. Not sure what 0x200 signifies though.

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