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

[David Daney <ddaney.cavm@gmail.com>]

On 01/09/2015 05:23 AM, Daniel Sanders wrote:
> Hi,
>
> Thanks for the quick reply.
>
>> -----Original Message-----
>> From: Sergei Shtylyov [mailto:sergei.shtylyov@cogentembedded.com]
>> Sent: 09 January 2015 12:18
>> To: Daniel Sanders; linux-mips@linux-mips.org; Ralf Baechle
>> Cc: 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
>>
>> Hello.
>>
>> On 1/9/2015 3:06 PM, Daniel Sanders wrote:
>>
>>> Without this, a 'break' instruction is executed very early in the boot and
>>> the boot hangs.
>>
>>> The problem is that clang doesn't honour named registers on local variables
>>> and silently treats them as normal uninitialized variables. However, it
>>> does honour them on global variables.

Why not fix clang instead?

>>
>>> 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.

>
> gcc gives:
> arch/mips/include/asm/thread_info.h:61:1: error: multiple storage classes in declaration specifiers
>   static register struct thread_info *current_gp_register asm("$28");
>   ^
>
> and clang gives:
> arch/mips/include/asm/thread_info.h:61:8: error: cannot combine with previous 'static' declaration specifier
> static register struct thread_info *current_gp_register asm("$28");
>         ^
>
>