linux-kernel - Re: [V6,1/9] elf: Add new powerpc specifc core note sections

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Message-ID: <1428534695.4682.18.camel@neuling.org>
Date:	Thu, 09 Apr 2015 09:11:35 +1000
From:	Michael Neuling <mikey@...ling.org>
To:	Ulrich Weigand <Ulrich.Weigand@...ibm.com>
Cc:	Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
	akpm@...ux-foundation.org, avagin@...nvz.org, davej@...hat.com,
	davem@...emloft.net, dhowells@...hat.com,
	Edjunior Barbosa Machado <emachado@...ux.vnet.ibm.com>,
	james.hogan@...tec.com, kirjanov@...il.com,
	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	oleg@...hat.com, palves@...hat.com, Paul.Clothier@...tec.com,
	peterz@...radead.org, sam.bobroff@....ibm.com,
	shuahkh@....samsung.com, sukadev@...ux.vnet.ibm.com,
	tglx@...utronix.de
Subject: Re: [V6,1/9] elf: Add new powerpc specifc core note sections

On Wed, 2015-04-08 at 19:50 +0200, Ulrich Weigand wrote:
> Anshuman Khandual <khandual@...ux.vnet.ibm.com> wrote on 23.03.2015
> 11:34:30:
> 
> > > With that in mind, do we have a way to set the top 32bits of the MSR
> > > (which contain the TM bits) when ptracing 32 bit processes?  I can't
> > > find anything like that in this patch set.
> >
> > No, we dont have that yet. When ptracing in 32-bit mode the MSR value
> > which can be viewed or set from the user space through PTRACE_GETREGS
> > PTRACE_SETREGS call is it's lower 32 bits only. Either we can club
> > the upper 32 bits of MSR as part of one of the ELF core notes we are
> > adding in the patch series or we can create one more separate ELF core
> > note for that purpose. Let me know your opinion on this.
> 
> I'm not sure I understand this.  I thought we had the following:
> 
> - If the process calling ptrace is itself 64-bit (which is how GDB is
>   built on all current Linux distributions), then PTRACE_GETREGS etc.
>   will *always* operate on 64-bit register sets, even if the target
>   process is 32-bit.
> 
> - If the process calling ptrace is 32-bit, then PTRACE_GETREGS will
>   operate on 32-bit register sets.   However, there is a separate
>   PTRACE_GETREGS64 / PTRACE_SETREGS64 call that will also provide
>   the opportunity to operate on the full 64-bit register set.  Both
>   apply independently of whether the target process is 32-bit or
>   64-bit.
> 
> Is this not correct?

I think you're correct.  We should be right.  I'd forgotten about the
GET/SETREGS64 interfaces.

Mikey

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