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

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Date:	Wed, 8 Apr 2015 19:50:50 +0200
From:	Ulrich Weigand <Ulrich.Weigand@...ibm.com>
To:	Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:	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,
	Michael Neuling <mikey@...ling.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

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?

Bye,
Ulrich

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