Re: ColdFire and Thread-Local Storage

[Sebastian Huber <sebastian.huber@embedded-brains.de>]

On 2014-01-28 20:15, Ian Lance Taylor wrote:
> On Tue, Jan 28, 2014 at 7:49 AM, Sebastian Huber
> <sebastian.huber@embedded-brains.de> wrote:
>>
>> it seems GCC uses this ColdFire TLS ABI:
>>
>> https://lists.debian.org/debian-68k/2007/11/msg00071.html
>>
>> Here we have a function
>>
>> void *__m68k_read_tp(void)
>>
>> which must return the thread pointer in register a0.
>>
>> I have to implement this function.  Is there a way to instruct GCC to return
>> the value in register a0 instead of d0 or do I have to use assembler to
>> implement this function?
>
> I believe that on m68k GNU/Linux a function that returns a pointer
> will normally return the value in a0.
>
> Ian
>

The function

void *__m68k_read_tp(void)
{
   const Thread_Control *executing = _Thread_Get_executing();

   return (char *) executing->Start.tls_area +
     _TLS_Get_thread_control_block_area_size((uintptr_t) _TLS_Alignment)
     + 0x7000;
}

translates to

__m68k_read_tp:
         move.l #_TLS_Alignment,%d0
         moveq #8,%d1
         move.l _Per_CPU_Information+18,%a0
         cmp.l %d0,%d1
         jls .L2
         moveq #8,%d0
.L2:
         add.l #28672,%d0
         add.l 194(%a0),%d0
         rts

I use now:

void __m68k_read_tp(void)
{
   const Thread_Control *executing = _Thread_Get_executing();
   void *tp = (char *) executing->Start.tls_area +
     _TLS_Get_thread_control_block_area_size((uintptr_t) _TLS_Alignment)
     + 0x7000;

   __asm__ volatile (
     "move.l %0, %%a0"
     :
     : "d" (tp)
   );
}

-- 
Sebastian Huber, embedded brains GmbH

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