From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from wproxy.gmail.com (wproxy.gmail.com [64.233.184.202]) by ozlabs.org (Postfix) with ESMTP id D979767B79 for ; Wed, 6 Jul 2005 01:45:57 +1000 (EST) Received: by wproxy.gmail.com with SMTP id i6so906007wra for ; Tue, 05 Jul 2005 08:45:55 -0700 (PDT) Message-ID: <4dd15d1805070508451b76afae@mail.gmail.com> Date: Tue, 5 Jul 2005 11:45:55 -0400 From: David Ho To: appro@fy.chalmers.se, linuxppc-embedded@ozlabs.org In-Reply-To: <4dd15d1805070508312427a0ba@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 References: <19EE6EC66973A5408FBE4CB7772F6F0A02C8770E@ltnmail.xyplex.com> <4dd15d1805070508312427a0ba@mail.gmail.com> Subject: Fwd: PPC bn_div_words routine rewrite Reply-To: David Ho List-Id: Linux on Embedded PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , This is the second confirmed report of the same problem on the ppc8xx. After reading my email. I must say I was the unfriendly one, I apologize for that. More debugging evidence to come. ---------- Forwarded message ---------- From: Murch, Christopher Date: Jul 1, 2005 9:46 AM Subject: RE: PPC bn_div_words routine rewrite To: David Ho David, I had observed the same issue on ppc 8xx machines after upgrading to the as= m version of the BN routines. Thank you very much for your work for the fix. My question is, do you have high confidence in the other new asm ppc BN routines after observing this issue or do you think they might have similia= r problems? Thanks. Chris -----Original Message----- From: David Ho [mailto:davidkwho@gmail.com] Sent: Thursday, June 30, 2005 6:22 PM To: openssl-dev@openssl.org; linuxppc-embedded@ozlabs.org Subject: Re: PPC bn_div_words routine rewrite The reason I had to redo this routine, in case anyone is wondering, is because ssh-keygen segfaults when this assembly routine returns junk to the BN_div_word function. On a ppc, if you issue the command ssh-keygen -t rsa1 -f /etc/ssh/ssh_host_key -N "" The program craps out when it tries to write the public key in ascii decimal. Regards, David On 6/30/05, David Ho wrote: > Hi all, > > This is a rewrite of the bn_div_words routine for the PowerPC arch, > tested on a MPC8xx processor. > I initially thought there is maybe a small mistake in the code that > requires a one-liner change but it turns out I have to redo the > routine. > I guess this routine is not called very often as I see that most other > routines are hand-crafted, whereas this routine is compiled from a C > function that apparently has not gone through a whole lot of testing. > > I wrote a C function to confirm correctness of the code. > > unsigned long div_words (unsigned long h, > unsigned long l, > unsigned long d) > { > unsigned long i_h; /* intermediate dividend */ > unsigned long i_q; /* quotient of i_h/d */ > unsigned long i_r; /* remainder of i_h/d */ > > unsigned long i_cntr; > unsigned long i_carry; > > unsigned long ret_q; /* return quotient */ > > /* cannot divide by zero */ > if (d =3D=3D 0) return 0xffffffff; > > /* do simple 32-bit divide */ > if (h =3D=3D 0) return l/d; > > i_q =3D h/d; > i_r =3D h - (i_q*d); > ret_q =3D i_q; > > i_cntr =3D 32; > > while (i_cntr--) > { > i_carry =3D (l & 0x80000000) ? 1:0; > l =3D l << 1; > > i_h =3D (i_r << 1) | i_carry; > i_q =3D i_h/d; > i_r =3D i_h - (i_q*d); > > ret_q =3D (ret_q << 1) | i_q; > } > > return ret_q; > } > > > Then I handcrafted the routine in PPC assembly. > The result is a 26 line assembly that is easy to understand and > predictable as opposed to a 81liner that I am still trying to > decipher... > If anyone is interested in incorporating this routine to the openssl > code I'll be happy to assist. > At this point I think I will be taking a bit of a break from this 3 > day debugging/fixing marathon. > > Regards, > David Ho > > > # > # Handcrafted version of bn_div_words > # > # r3 =3D h > # r4 =3D l > # r5 =3D d > > cmplwi 0,r5,0 # compare r5 and 0 > bc BO_IF_NOT,CR0_EQ,.Lppcasm_div1 # proceed if d!=3D0 > li r3,-1 # d=3D0 return -1 > bclr BO_ALWAYS,CR0_LT > .Lppcasm_div1: > cmplwi 0,r3,0 # compare r3 and 0 > bc BO_IF_NOT,CR0_EQ,.Lppcasm_div2 # proceed if h !=3D 0 > divwu r3,r4,r5 # ret_q =3D l/d > bclr BO_ALWAYS,CR0_LT # return result in r3 > .Lppcasm_div2: > divwu r9,r3,r5 # i_q =3D h/d > mullw r10,r9,r5 # i_r =3D h - (i_q*d) > subf r10,r10,r3 > mr r3,r9 # req_q =3D i_q > .Lppcasm_set_ctr: > li r12,32 # ctr =3D bitsizeof(d) > mtctr r12 > .Lppcasm_div_loop: > addc r4,r4,r4 # l =3D l << 1 -> i_carry > adde r11,r10,r10 # i_h =3D (i_r << 1) | i_carry > divwu r9,r11,r5 # i_q =3D i_h/d > mullw r10,r9,r5 # i_r =3D i_h - (i_q*d) > subf r10,r10,r11 > add r3,r3,r3 # ret_q =3D ret_q << 1 | i_q > add r3,r3,r9 > bc BO_dCTR_NZERO,CR0_EQ,.Lppcasm_div_loop > .Lppc_div_end: > bclr BO_ALWAYS,CR0_LT # return result in r3 > .long 0x00000000 > _______________________________________________ Linuxppc-embedded mailing list Linuxppc-embedded@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-embedded