Re: [PATCHv2 1/4] x86_64: cleanup THREAD_INFO(reg,offset) macro

[Borislav Petkov]

On Wed, Jan 21, 2015 at 05:20:09PM +0100, Alexander van Heukelum wrote:
> On Wed, Jan 21, 2015, at 14:40, Denys Vlasenko wrote:
> > On Sun, Jan 18, 2015 at 12:45 PM, Alexander van Heukelum
> > <heukelum@xxxxxxxxxxx> wrote:
> > > The macro THREAD_INFO(reg,offset) is used in assembly to compute the
> > > offset between the user ptregs and the thread_info struct. Change
> > > the macro and all its uses so that offset is given as the current
> > > top of stack in the pt_regs frame. The generated code is identical.
> > 
> > What is the purpose of doing this?
> > 
> > I don't mean to say that it's pointless, but it is also not obvious
> > why it's better than the code before patch.
> 
> Just because I had a hard time understanding what the offset
> parameter means. Turns out Borislav did another variant in his
> patchset. Quoting him from the commit message which made
> that the change:
> > Semi-mysterious expressions THREAD_INFO(%rsp,RIP) - "why RIP??"
> > are now replaced by more logical THREAD_INFO(%rsp,SIZEOF_PTREGS) -
> > "rsp is SIZEOF_PTREGS bytes below the top, calculate
> > thread_info's address using that information"
> 
> Borislav expresses "offset" as an offset from the stack's page
> boundary,while I chose the offset from the start of struct
> pt_regs on the stack.

I've never done any such thing :-)

s/Borislav/Denys/g.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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