[OpenBIOS] [PATCH, RFC 6/6] ppc: Fix stack setup
agraf at suse.de
Mon Oct 11 11:16:52 CEST 2010
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.
>> 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 code
> a little of course.
I'd personally say go for simplicity.
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