[OpenBIOS] [RFC 3/3] ppc: RTAS WIP
agraf at suse.de
Fri Oct 15 22:28:26 CEST 2010
On 15.10.2010, at 22:22, Andreas Färber wrote:
> [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 :
> 7.2.2 Register Usage
> 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.
Read: no timers, no paging, no modification of page fault handler registers
> 7-11. RTAS must preserve the following user mode registers: R1-R2, R13-R31, and CR.
Except for CR, C is the same. So you really only need to save/restore cr :).
> 7–12. RTAS must preserve the following operating environment registers: MSR, DAR, DSISR, IBAT0-IBAT3, and DBAT0-DBAT3.
Read: You're allowed to change direct mappings, but need to restore them when exiting again. Interesting :).
More information about the OpenBIOS