Re: 2.6.37-rc7: Regression: b43: crashes in hwrng_register()

[Mario 'BitKoenig' Holbe]

On Fri, Jan 07, 2011 at 12:35:41AM +1100, Herbert Xu wrote:
> On Thu, Jan 06, 2011 at 02:15:16PM +0100, Mario 'BitKoenig' Holbe wrote:
> > 1. Having ECX on the clobber-list is not really necessary.
> > XSTORE doesn't touch ECX at all.
> > REP XSTORE would touch it, but for this ECX would be an input anyways.
> 
> The documentation wasn't clear whether ECX would be updated without
> the REP prefix so I included it to be on the safe side.  Unfortunately
> my only VIA machine is on another continent at the moment so I can't
> test it myself.  Can you verify that ECX isn't changed without the
> REP prefix?

session-log (including small test case) attached: ECX is not changed.

> > 2. Would you mind doing the same for EDX as you did for EDI?
> According to my documentation EDX isn't be modified (nor would it
> make sense as it would break REP XSTORE).  Are you seeing anything
> different?

http://linux.via.com.tw/support/beginDownload.action?eleid=181&fid=261
VIA PadLock Programming Guide, v1.66, 4th August 2005
2.1 XSTORE Instructions (page 9)
RNG Quality Factor: EDX
[...] Only the lower two bits of EDX are meaningful; the upper 30 bits
are ignored by the instruction and may be set to zero.
                                   ^^^^^^^^^^^^^^^^^^

http://hackipedia.org/Hardware/CPU/x86/chip,%20VIA/nano/Padlock,%20quick%20reference%20v0.95%20(July%2025th,%202008).pdf
PadLock Quick Reference, v0.95, 25th July 2008
RANDOM NUMBER GENERATION (page 3)
Register Usage: Output
EDX Bits 0:1 are unchanged, all higher order bits are zero.
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

See the attached session-log as well: those EDX bits are indeed zeroed.


Btw: I believe both documents are quite clear regarding ECX for XSTORE.


Mario
-- 
User sind wie ideale Gase - sie verteilen sich gleichmaessig ueber alle Platten
holbe@ideapad ~ % cat via-rng-test.c
#include <stdio.h>
#include <string.h>

static inline unsigned long xstore(unsigned long *addr, unsigned long edx)
{
	unsigned long eax_out;
	unsigned long ecx = 0xaa55aa55;
	int ts_state;

	printf("ecx: %08lx\tedx: %08lx\tedi: %p\n", ecx, edx, addr);

	asm(".byte 0x0F,0xA7,0xC0 /* xstore %%edi (addr=%0) */"
		: "=m" (*addr), "=a" (eax_out), "+D" (addr), "+d" (edx), "+c" (ecx));

	printf("ecx: %08lx\tedx: %08lx\tedi: %p\n", ecx, edx, addr);

	return eax_out;
}

int main(void) {
	unsigned long addr[8];

	memset(addr, 0, sizeof(addr));

	printf("%p: %08lx\n", addr, *(unsigned long *)addr);
	xstore(addr, 0xffffff03); /* 8 rand bits, 32 stored bits */
	printf("%p: %08lx\n", addr, *(unsigned long *)addr);

	return 0;
}
holbe@ideapad ~ % gcc -o via-rng-test via-rng-test.c
holbe@ideapad ~ % ./via-rng-test
0xbff09d40: 00000000
ecx: aa55aa55   edx: ffffff03   edi: 0xbff09d40
ecx: aa55aa55   edx: 00000003   edi: 0xbff09d48
0xbff09d40: 339d4525
holbe@ideapad ~ %

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