[OpenBIOS] [PATCH, RFC 6/6] ppc: Fix stack setup
andreas.faerber at web.de
Mon Oct 11 12:32:07 CEST 2010
Am 11.10.2010 um 11:16 schrieb Alexander Graf:
> Andreas Färber wrote:
>> Am 11.10.2010 um 04:53 schrieb Segher Boessenkool:
>>>> + mfpvr r14 /* check if ppc64 */
>>>> + li r15, 4
>>>> + srw r14, r14, r15 /* >> 4 */
>>> srwi 14,14,4
>>> but you actually want to shift 16, not 4.
>>>> + cmplwi r14, 0x33
>>>> + blt 1f
>>>> + cmplwi r14, 0x7033
>>>> + bge 1f
>>> This is too simplistic.
>> Are you saying the original is_ppc64() function I transformed into
>> assembler code is wrong, too?
>> static int is_ppc64(void)
>> unsigned int pvr;
>> asm volatile("mfspr %0, 0x11f" : "=r" (pvr) );
>> return ((pvr >= 0x330000) && (pvr < 0x70330000));
> In here we don't know if SF=1 because we forcefully disable it always.
Ah! You mean this?
li r0, 0
That would mean I don't need a 64-bit RTAS unless AIX sets SF=1. :)
>>> Here's something that detects
>>> whether the CPU is currently in 64-bit mode, without
>>> using 64-bit-only instructions:
>>> lis 3,0x4000
>>> add 3,3,3
>>> addc 3,3,3
>>> adde 3,3,3
>>> cmplwi 3,0
>>> beq 64bit
>>> bne 32bit
>> Thanks! I'll give it a try.
>>> Anyway, can't you always align to 128 bytes, and create
>>> one frame for the 64-bit ABI? Or do you really want to
>>> save those few bytes...
>> As for "those few bytes", I guess I mixed up bits and hexadecimal
>> digits once again. An example:
>> -m 1024
>> RAM 0..0x40000000
>> OpenBIOS @ 0x3ff00000
>> Hash table @ 0x3fef0000 vs. 0x3fe00000
>> We'd be wasting 960 KiB. If that's acceptable, it'll simplify the
>> a little of course.
> I'd personally say go for simplicity.
On second thoughts, unfortunately I don't think 32-bit CPUs can handle
clrrdi, so we'd still need the distinction here since we're
subtracting from RAM size.
Or better, we'd need a distinction at the original setup of r1, so
that it fits into the low 32 or 31 bits in the first place. Currently
everything over -m 2048 would overlap with ISA and at some point PCI
and fw_cfg. Memory would probably have to become non-contiguous then,
breaking some more assumptions...
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