[OpenBIOS] [RFC 3/3] ppc: RTAS WIP

[Andreas Färber]

[2nd try]

Am 15.10.2010 um 12:26 schrieb Alexander Graf:

> On 15.10.2010, at 00:38, Alexander Graf wrote:
>
>> /* saving non-volatile registers */
>>
>>> +    stw r13,  8(r4)
>>
>> I would recommend multiplying here:
>>
>> stw r13, (3 * 4)(r4)
>>
>> That makes it more readable.
>>
>>> +    stw r14, 12(r4)
>>> +    stw r15, 16(r4)
>>> +    stw r16, 20(r4)
>>> +    stw r17, 24(r4)
>>> +    stw r18, 28(r4)
>>> +    stw r19, 32(r4)
>>> +    stw r20, 36(r4)
>>> +    stw r21, 40(r4)
>>> +    stw r22, 44(r4)
>>> +    stw r23, 48(r4)
>>> +    stw r24, 52(r4)
>>> +    stw r25, 56(r4)
>>> +    stw r26, 60(r4)
>>> +    stw r27, 64(r4)
>>> +    stw r28, 68(r4)
>>> +    stw r29, 72(r4)
>>> +    stw r30, 76(r4)
>>> +    stw r31, 80(r4)
>
> Actually thinking about this a bit more, r13-r31 are already defined  
> non-volatile by the C ABI, so you can be sure that the C function  
> you're calling doesn't clobber them. You don't need to manually save/ 
> restore them :).

The OF client interface saves r5-r31 as well as ctr, cr and xer.
It shouldn't hurt to save more registers than necessary to assert the  
requirements of the CHRP spec [1]:

<<<
7.2.2 Register Usage

Requirements:

7–10. Except as required by a specific function, RTAS must not modify  
the following operating environment registers: TB, DEC, SPRG0-SPRG3,  
EAR, DABR, SDR1, ASR, SR0-SR15, FPSCR, FPR0-FPR3, and any processor  
specific registers.

7-11. RTAS must preserve the following user mode registers: R1-R2, R13- 
R31, and CR.

7–12. RTAS must preserve the following operating environment  
registers: MSR, DAR, DSISR, IBAT0-IBAT3, and DBAT0-DBAT3.
 >>>

Andreas

[1] ftp://ftp.software.ibm.com/rs6000/technology/spec/chrp/ 
hrpa_103.ps.Z (p.94)