RE: [PATCH] MIPS: Changed current_thread_info() to an equivalent supported by both clang and GCC

From: Daniel Sanders <Daniel.Sanders@imgtec.com>
To: David Daney <ddaney.cavm@gmail.com>
Cc: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>,
	"linux-mips@linux-mips.org" <linux-mips@linux-mips.org>,
	Ralf Baechle <ralf@linux-mips.org>,
	Paul Burton <Paul.Burton@imgtec.com>,
	Markos Chandras <Markos.Chandras@imgtec.com>,
	James Hogan <James.Hogan@imgtec.com>,
	"Behan Webster" <behanw@converseincode.com>
Subject: RE: [PATCH] MIPS: Changed current_thread_info() to an equivalent supported by both clang and GCC
Date: Sat, 10 Jan 2015 12:53:22 +0000	[thread overview]
Message-ID: <E484D272A3A61B4880CDF2E712E9279F458E8336@hhmail02.hh.imgtec.org> (raw)
In-Reply-To: <54B069D4.4090608@gmail.com>

> -----Original Message-----
> From: David Daney [mailto:ddaney.cavm@gmail.com]
> Sent: 09 January 2015 23:53
> To: Daniel Sanders
> Cc: Sergei Shtylyov; linux-mips@linux-mips.org; Ralf Baechle; Paul Burton;
> Markos Chandras; James Hogan; Behan Webster
> Subject: Re: [PATCH] MIPS: Changed current_thread_info() to an equivalent
> supported by both clang and GCC
> 
> On 01/09/2015 12:06 PM, Daniel Sanders wrote:
> >> -----Original Message-----
> >> From: David Daney [mailto:ddaney.cavm@gmail.com]
> [...]
> 
> >
> >>>>> Signed-off-by: Daniel Sanders <daniel.sanders@imgtec.com>
> >>>>
> >>>> [...]
> >>>>
> >>>>> diff --git a/arch/mips/include/asm/thread_info.h
> >>>> b/arch/mips/include/asm/thread_info.h
> >>>>> index 99eea59..2a2f3c4 100644
> >>>>> --- a/arch/mips/include/asm/thread_info.h
> >>>>> +++ b/arch/mips/include/asm/thread_info.h
> >>>>> @@ -58,11 +58,11 @@ struct thread_info {
> >>>>>     #define init_stack		(init_thread_union.stack)
> >>>>>
> >>>>>     /* How to get the thread information struct from C.  */
> >>>>> +register struct thread_info *current_gp_register asm("$28");
> >>>>
> >>>>       *static* missing?
> >>>>
> >>>> WBR, Sergei
> >>>
> >>> Combining 'register' and 'static' is invalid.
> >>
> >> Defining global variables in header files is also invalid.
> >
> > I agree with that statement but named register globals are not the same as
> normal global variables. In particular, they do not take up space in the data
> section and they do not have an entry in the symbol table. They can therefore
> be included in multiple objects without causing link errors.
> >
> 
> Well, the GCC manual seems to bless your usage, so I withdraw my
> objection on making this global.  But, changing the name to
> "current_gp_register" removes information about what it is used for.
> 
> Can you resend that patch so that it still has the name
> "__current_thread_info", and only moves it to the global scope?
> 
> Thanks,
> David Daney

Sure. I'll Cc you directly on the re-send.

The main reason I renamed it is that identifiers starting with '__' are reserved. It's pretty unlikely but it's possible that the name will conflict with a C implementation in the future.