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