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

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Date:	Mon, 19 May 2014 15:43:21 +0100
From:	Pedro Alves <palves@...hat.com>
To:	Anshuman Khandual <khandual@...ux.vnet.ibm.com>
CC:	mikey@...ling.org, avagin@...nvz.org, linux-kernel@...r.kernel.org,
	oleg@...hat.com, michael@...erman.id.au, linuxppc-dev@...abs.org
Subject: Re: [PATCH V2 2/3] powerpc, ptrace: Enable support for transactional
 memory register sets

On 05/19/2014 12:46 PM, Anshuman Khandual wrote:

>> > I couldn't actually find any arch that currently returns -ENODEV in
>> > the "active" hook.  I see that binfmt_elf.c doesn't handle
>> > regset->active() returning < 0.  Guess that may be why.  Looks like
>> > something that could be cleaned up, to me.
>> >
> Also it does not consider the return value of regset->active(t->task, regset)
> (whose objective is to figure out whether we need to request regset->n number
> of elements or less than that) in the subsequent call to regset->get function.

Indeed.

TBC, do you plan on fixing this?  Otherwise ...

> Now coming to the installation of the .active hooks part for all the new regsets, it
> should be pretty straight forward as well. Though its optional and used for elf_core_dump
> purpose only, its worth adding them here. Example of an active function should be something
> like this. The function is inexpensive as required.
> 
> +static int tm_spr_active(struct task_struct *target,
> +                               const struct user_regset *regset)
> +{
> +       if (!cpu_has_feature(CPU_FTR_TM))
> +               return -ENODEV;

... unfortunately this will do the wrong thing.

Thanks,
-- 
Pedro Alves

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