* Re: PPC bn_div_words routine rewrite [not found] <4dd15d1805063003587276af7e@mail.gmail.com> @ 2005-06-30 22:22 ` David Ho 2005-07-01 17:36 ` Andy Polyakov 0 siblings, 1 reply; 10+ messages in thread From: David Ho @ 2005-06-30 22:22 UTC (permalink / raw) To: openssl-dev, linuxppc-embedded 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 decima= l. Regards, David=20 On 6/30/05, David Ho <davidkwho@gmail.com> wrote: > Hi all, >=20 > 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. >=20 > I wrote a C function to confirm correctness of the code. >=20 > 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 */ >=20 > unsigned long i_cntr; > unsigned long i_carry; >=20 > unsigned long ret_q; /* return quotient */ >=20 > /* cannot divide by zero */ > if (d =3D=3D 0) return 0xffffffff; >=20 > /* do simple 32-bit divide */ > if (h =3D=3D 0) return l/d; >=20 > i_q =3D h/d; > i_r =3D h - (i_q*d); > ret_q =3D i_q; >=20 > i_cntr =3D 32; >=20 > while (i_cntr--) > { > i_carry =3D (l & 0x80000000) ? 1:0; > l =3D l << 1; >=20 > i_h =3D (i_r << 1) | i_carry; > i_q =3D i_h/d; > i_r =3D i_h - (i_q*d); >=20 > ret_q =3D (ret_q << 1) | i_q; > } >=20 > return ret_q; > } >=20 >=20 > 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. >=20 > Regards, > David Ho >=20 >=20 > # > # Handcrafted version of bn_div_words > # > # r3 =3D h > # r4 =3D l > # r5 =3D d >=20 > 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 > ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: PPC bn_div_words routine rewrite 2005-06-30 22:22 ` PPC bn_div_words routine rewrite David Ho @ 2005-07-01 17:36 ` Andy Polyakov 2005-07-04 14:35 ` David Ho 0 siblings, 1 reply; 10+ messages in thread From: Andy Polyakov @ 2005-07-01 17:36 UTC (permalink / raw) To: openssl-dev; +Cc: linuxppc-embedded > 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. If would help if you provide evidence such as debugger stack trace and program output. Provided description makes no sense. "seg-faults when routine returns junk to BN_div_word"? Seg-fault [segmentation violation] can occur when you write something to memory and nothing gets written to memory upon result return. BN_div_word does write to memory, but I fail to see how a bogus value could possibly trigger seg-fault. The only possibility is that assembler doesn't follow ABI convention and corrupts registers, which caller is using/expects to be preserved by callee. There're several PPC ABI flavors in use, but OpenSSL routines were designed ABI-neutral, Well, "neutrality" really means "common denominator for ABI specs examined at the moment of coding," so there is a window of opportunity that it won't be "neutral" to future ABI, but is it really case? That your system uses some newly designed PPC ABI? You never mentioned what's your system... But you're apparently right about a bug being present in PPC assembler. I too have got insane [with very few significant digits] decimal printout of public key generated by ssh-keygen... >>This is a rewrite of the bn_div_words routine for the PowerPC arch, >>tested on a MPC8xx processor. Well, suggested routine apparently sends ssh-keygen on the PPC-based 32-bit system I have access to to an end-less loop... And (cd test; make test_bn) fails early in BN_sqr... And test/exptest fails miserably with "bad reciprocal"... >>I initially thought there is maybe a small mistake in the code that >>requires a one-liner change But apparently this appears to be the case! Please verify following: --- crypto/bn/asm/ppc.pl.orig 2004-04-28 00:05:50.000000000 +0200 +++ crypto/bn/asm/ppc.pl 2005-07-01 18:58:21.105656512 +0200 @@ -1717,7 +1717,7 @@ li r9,1 # r9=1 $SHL r10,r9,r8 # r9<<=r8 $UCMP 0,r3,r10 # - bc BO_IF,CR0_GT,Lppcasm_div2 #or if (h > (1<<r8)) + bc BO_IF_NOT,CR0_GT,Lppcasm_div2 #or if (h > (1<<r8)) $UDIV r3,r3,r0 #if not assert(0) divide by 0! #that's how we signal overflow bclr BO_ALWAYS,CR0_LT #return. NEVER REACHED. A. ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: PPC bn_div_words routine rewrite 2005-07-01 17:36 ` Andy Polyakov @ 2005-07-04 14:35 ` David Ho 2005-07-05 15:00 ` Andy Polyakov 0 siblings, 1 reply; 10+ messages in thread From: David Ho @ 2005-07-04 14:35 UTC (permalink / raw) To: openssl-dev; +Cc: linuxppc-embedded [-- Attachment #1: Type: text/plain, Size: 5108 bytes --] Good morning gentleman, Let's start the week off with less hostility and more productive criticism on this topic. As I see it, the popular Linux distributions are not that interested on ppc32 since neither Novell nor Redhat openly support this arch. We will have to put our heads together to make ppc32 a stable Linux platform. On 7/1/05, Andy Polyakov <appro@fy.chalmers.se> wrote: > BN_div_word does write to memory, but I fail > to see how a bogus value could possibly trigger seg-fault. Assuming that you are a maintainer of the openssl code, which I gather you are, would you even care to take the time to examine the code in suspect, or find someone who is capable of doing that, I'm sure you must have a lot of friends, at least one who is knowledgeable in the ppc32 arch. > The only > possibility is that assembler doesn't follow ABI convention and corrupts > registers, which caller is using/expects to be preserved by callee. > There're several PPC ABI flavors in use, but OpenSSL routines were > designed ABI-neutral, Well, "neutrality" really means "common > denominator for ABI specs examined at the moment of coding," so there is > a window of opportunity that it won't be "neutral" to future ABI, but is > it really case? I don't understand the terminology you use here. As I understand it ABI is there so binaries can inter-operate in the case of dynamic loading, when the ABI is consistent you can use any compiler that conforms to the ABI and those binaries can work together. As I see it I'm building openssl and openssh with the same compiler so what is the real issue here? Or is it an issue at all? If you are referring to C calling convention, then I can only guess you have figured it out or otherwise none of the assembly routine will work. > That your system uses some newly designed PPC ABI? You > never mentioned what's your system... In my very first email, I have already said quote "tested on a MPC8xx processor" and I am using 2.4.24 which is nothing close to the bleeding edge so I reckon the ABI is fairly standard. Do you have any experience with the PowerPC arch? > But you're apparently right about a bug being present in PPC assembler. So you are saying there is a bug in the GCC assembler? How confident are you in that? Is the first correct step to examine the assembly code for errors before jumping to any conclusion that the GCC assembler is bad? > >>This is a rewrite of the bn_div_words routine for the PowerPC arch, > >>tested on a MPC8xx processor. > > Well, suggested routine apparently sends ssh-keygen on the PPC-based > 32-bit system I have access to to an end-less loop... If you care to read the c function I supplied or if you don't believe it: If you understand ppc 32-bit instructions, as specified in the PowerPC Microprocessor Family: Programming Environments for 32-Bit Microprocessors. My routine would not be able to find a condition that will make it go into an end-less loop,unless you messed up bad somewhere. > And (cd test; make > test_bn) fails early in BN_sqr... And test/exptest fails miserably with > "bad reciprocal"... I don't know what you did but (make test_bn) works for me. So I question how diligently you are in setting up the tests. If you are busy, please get one of your ppc friends to do it. > >>I initially thought there is maybe a small mistake in the code that > >>requires a one-liner change > > But apparently this appears to be the case! Please verify following: > > --- crypto/bn/asm/ppc.pl.orig 2004-04-28 00:05:50.000000000 +0200 > +++ crypto/bn/asm/ppc.pl 2005-07-01 18:58:21.105656512 +0200 > @@ -1717,7 +1717,7 @@ > li r9,1 # r9=1 > $SHL r10,r9,r8 # r9<<=r8 > $UCMP 0,r3,r10 # > - bc BO_IF,CR0_GT,Lppcasm_div2 #or if (h > (1<<r8)) > + bc BO_IF_NOT,CR0_GT,Lppcasm_div2 #or if (h > (1<<r8)) > $UDIV r3,r3,r0 #if not assert(0) divide by 0! > #that's how we signal overflow > bclr BO_ALWAYS,CR0_LT #return. NEVER REACHED. > You don't think I have gone in and fix that before realizing it's worse than that? I am sure you didn't think I spend 3 days out in the beach and somehow come up with an idea of clobbering some useful routine because I think my routine is better? In summary, what I am trying to provide the community is an alternative to do something, the current implementation of which is very questionable. You might resist change which is understandable. But I were a diligent maintainer and I realize something is broken in my code, then I will put the time to investigate the problem. If I don't have the time, I will delagate it to a friend. If I don't have a friend with that expertise then, I will try to make friends with the reporter of the bug since he will most likely have spent hours fixing the problem. Regards, David Ho. [-- Attachment #2: test_bn.txt --] [-- Type: text/plain, Size: 3397 bytes --] bash-2.05b# make test_bn starting big number library test, could take a while... test BN_add test BN_sub test BN_lshift1 test BN_lshift (fixed) test BN_lshift test BN_rshift1 test BN_rshift test BN_sqr test BN_mul test BN_div test BN_div_recp test BN_mod test BN_mod_mul test BN_mont test BN_mod_exp test BN_exp test BN_kronecker ...++++++ .................................................................................................... test BN_mod_sqrt ..... ..... ..... ..... ..... ..... ..... ..... .......++++++++++++ ..... ......++++++++++++ ..... ...++++++++++++ ..... ..++++++++++++ ..... ...++++++++++++ ..... ........++++++++++++ ..... .................++++++++++++ ..... ...........++++++++++++ ..... running bc verify BN_add.................................................................................................... verify BN_sub...................................................................................................................................................... verify BN_lshift1.................................................................................................... verify BN_lshift (fixed).................................................................................................... verify BN_lshift.................................................................................................... verify BN_rshift1.................................................................................................... verify BN_rshift.................................................................................................... verify BN_sqr.................................................................................................... verify BN_mul...................................................................................................................................................... verify BN_div............................................................................................................................................................................................................................................................................................................ verify BN_div_recp............................................................................................................................................................................................................................................................................................................ verify BN_mod.................................................................................................... verify BN_mod_mul............................................................................................................................................................................................................................................................................................................ verify BN_mont..... verify BN_mod_exp..... verify BN_exp..... verify BN_kronecker verify BN_mod_sqrt 2015 tests passed test a^b%c implementations ../util/shlib_wrap.sh ./exptest ........................................................................................................................................................................................................ done ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: PPC bn_div_words routine rewrite 2005-07-04 14:35 ` David Ho @ 2005-07-05 15:00 ` Andy Polyakov 0 siblings, 0 replies; 10+ messages in thread From: Andy Polyakov @ 2005-07-05 15:00 UTC (permalink / raw) To: openssl-dev; +Cc: linuxppc-embedded > Let's start the week off with less hostility and more productive > criticism on this topic. If you want productivity, then provide real evidence in form of stack backtrace at segmentation violation point, disassemble output in the vicinity of segmentation violation point and 'info registers' output at the same point. As for hostility I leave it without comment, as you're apparently can outrank anybody in that area:-) >>But you're apparently right about a bug being present in PPC assembler. > > > So you are saying there is a bug in the GCC assembler? How confident > are you in that? Is the first correct step to examine the assembly > code for errors before jumping to any conclusion that the GCC > assembler is bad? Did I say GCC assembler? I said PPC assembler, which refers to crypto/bn/asm/ppc.pl. >>>>This is a rewrite of the bn_div_words routine for the PowerPC arch, >>>>tested on a MPC8xx processor. >> >>Well, suggested routine apparently sends ssh-keygen on the PPC-based >>32-bit system I have access to to an end-less loop... > > > If you care to read the c function I supplied or if you don't believe > it: If you understand ppc 32-bit instructions, as specified in the > PowerPC Microprocessor Family: Programming Environments for 32-Bit > Microprocessors. My routine would not be able to find a condition > that will make it go into an end-less loop,unless you messed up bad > somewhere. I didn't say that suggested routine goes into an end-less loop, but that it "*apparently* sends ssh-keygen into end-less loop." I made no claims about which routine exactly loops, and I even admit that I don't know for sure if it was in fact end-less loop, because I've chosen to kill the process after couple of minutes. Note that normally it takes just few seconds on the machine I've tested on, so that couple of minutes is essentially unacceptable and by all means *appears* as end-less loop. > In summary, what I am trying to provide the community is an > alternative to ... the current implementation of which is > very questionable. crypto/bn/asm/ppc.pl distributed with OpenSSL was designed for and explicitly tested by IBM under 32- and 64-bit PPC Linux, 32- and 64-bit AIX, as well as 32-bit MacOS X. Special care was taken to make sure that neither of ABIs/calling conventions used by above listed platforms are violated, so that module can be safely invoked by compiler-generated code for above mentioned OSes. Afterwards there were reports that it was successfully used on unspecified [in report] embedded PPC-based platform. Despite this on Friday I could personally confirm on 32-bit MacOS X that there admittedly was a bug in ppc.pl, which manifests as failure to generate sane decimal ASCII presentation of a BIGNUM, which is exactly the kind of operation taking place when you run ssh-keygen -t rsa1 [it should be noted decimal ASCII is unfortunately not covered by 'make test_bn' suite]. But under no circumstances segmentation violation was observed. At the same time I could personally confirm that if pasted into osx32_ppc.s, suggested implementation induces 'make test_bn' failure on 32-bit MacOS X. In particular test/bntest terminates with print "test BN_sqr\n" -FF554CAEAE * -FF554CAEAE - FEAB0B30019BBA80FE44 Square test failed! 1 while test/exptest: BN_mod_exp_recp() problems 14482:error:03082065:bignum routines:BN_div_recp:bad reciprocal:bn_recp.c:194: For me it's enough reasons to become sceptical to submission and conduct trouble-shooting of my own. Currently available ppc.pl was verified to pass 'make test_bn' on 32-bit MacOS X, 32- and 64-bit AIX [tested by IBM], as well as to generate correct decimal ASCII presentation on the mentioned platforms. If it doesn't work for you, then submit information listed in the beginning of the letter. A. ^ permalink raw reply [flat|nested] 10+ messages in thread
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* Fwd: PPC bn_div_words routine rewrite [not found] ` <4dd15d1805070508312427a0ba@mail.gmail.com> @ 2005-07-05 15:45 ` David Ho 2005-07-05 16:36 ` David Ho 0 siblings, 1 reply; 10+ messages in thread From: David Ho @ 2005-07-05 15:45 UTC (permalink / raw) To: appro, linuxppc-embedded 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 <cmurch@mrv.com> Date: Jul 1, 2005 9:46 AM Subject: RE: PPC bn_div_words routine rewrite To: David Ho <davidkwho@gmail.com> 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 <davidkwho@gmail.com> 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 ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: PPC bn_div_words routine rewrite 2005-07-05 15:45 ` Fwd: " David Ho @ 2005-07-05 16:36 ` David Ho 2005-07-05 17:01 ` David Ho 0 siblings, 1 reply; 10+ messages in thread From: David Ho @ 2005-07-05 16:36 UTC (permalink / raw) To: appro, linuxppc-embedded, openssl-dev First pass debugging results from gdb on ppc8xx. Executing ssh-keygen with following arguments. (gdb) show args Argument list to give program being debugged when it is started is "-t rsa1 -f /etc/ssh/ssh_host_key -N """. Program received signal SIGSEGV, Segmentation fault. BN_bn2dec (a=3D0x1002d9f0) at bn_print.c:136 136 *lp=3DBN_div_word(t,BN_DEC_CONV); (gdb) i r r0 0x0 0 r1 0x7fffd580 2147472768 r2 0x30012868 805382248 r3 0x80000000 2147483648 r4 0xfef33fc 267334652 r5 0x25 37 r6 0xfccdef8 265084664 r7 0x7fffd4c0 2147472576 r8 0xfbad2887 4222429319 r9 0x84044022 2214871074 r10 0x0 0 r11 0x2 2 r12 0xfef2054 267329620 r13 0x10030bc8 268635080 r14 0x0 0 r15 0x0 0 r16 0x0 0 r17 0x0 0 r18 0x0 0 r19 0x0 0 r20 0x0 0 r21 0x0 0 r22 0x0 0 r23 0x64 100 r24 0x5 5 r25 0x1002d438 268620856 r26 0x1002d9f0 268622320 r27 0x1002c578 268617080 r28 0x1 1 r29 0x10031000 268636160 r30 0xffbf7d0 268171216 r31 0x1002d9f0 268622320 pc 0xfef2058 267329624 ps 0xd032 53298 cr 0x24044022 604258338 lr 0xfef2054 267329620 ctr 0xfccefa0 265088928 xer 0x20000000 536870912 fpscr 0x0 0 vscr 0x0 0 vrsave 0x0 0 (gdb) p/x $pc $1 =3D 0xfef2058 0x0fef2058 <BN_bn2dec+472>: stw r3,0(r29) (gdb) x 0x10031000 0x10031000: Cannot access memory at address 0x10031000 On 7/5/05, David Ho <davidkwho@gmail.com> wrote: > This is the second confirmed report of the same problem on the ppc8xx. >=20 > After reading my email. I must say I was the unfriendly one, I > apologize for that. >=20 > More debugging evidence to come. >=20 > ---------- Forwarded message ---------- > From: Murch, Christopher <cmurch@mrv.com> > Date: Jul 1, 2005 9:46 AM > Subject: RE: PPC bn_div_words routine rewrite > To: David Ho <davidkwho@gmail.com> >=20 >=20 > David, > I had observed the same issue on ppc 8xx machines after upgrading to the = asm > version of the BN routines. Thank you very much for your work for the fi= x. > 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 simil= iar > problems? > Thanks. > Chris >=20 > -----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 >=20 >=20 > 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 >=20 > ssh-keygen -t rsa1 -f /etc/ssh/ssh_host_key -N "" >=20 > The program craps out when it tries to write the public key in ascii > decimal. >=20 > Regards, > David >=20 > On 6/30/05, David Ho <davidkwho@gmail.com> 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 > ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: PPC bn_div_words routine rewrite 2005-07-05 16:36 ` David Ho @ 2005-07-05 17:01 ` David Ho 2005-07-05 20:21 ` David Ho 0 siblings, 1 reply; 10+ messages in thread From: David Ho @ 2005-07-05 17:01 UTC (permalink / raw) To: appro, linuxppc-embedded, openssl-dev I can tell you with certainty, with reference to the function BN_bn2dec, that since lp is a pointer, and within the while loop around bn_print.c:136 lp is being incremented. Because the test BN_is_zero(t) is always false, you have a pointer that is going off into the stratosphere, hence the segfault on ppc8xx. More analysis to come. On 7/5/05, David Ho <davidkwho@gmail.com> wrote: > First pass debugging results from gdb on ppc8xx. Executing ssh-keygen > with following arguments. >=20 > (gdb) show args > Argument list to give program being debugged when it is started is > "-t rsa1 -f /etc/ssh/ssh_host_key -N """. >=20 > Program received signal SIGSEGV, Segmentation fault. > BN_bn2dec (a=3D0x1002d9f0) at bn_print.c:136 > 136 *lp=3DBN_div_word(t,BN_DEC_CONV); >=20 > (gdb) i r > r0 0x0 0 > r1 0x7fffd580 2147472768 > r2 0x30012868 805382248 > r3 0x80000000 2147483648 > r4 0xfef33fc 267334652 > r5 0x25 37 > r6 0xfccdef8 265084664 > r7 0x7fffd4c0 2147472576 > r8 0xfbad2887 4222429319 > r9 0x84044022 2214871074 > r10 0x0 0 > r11 0x2 2 > r12 0xfef2054 267329620 > r13 0x10030bc8 268635080 > r14 0x0 0 > r15 0x0 0 > r16 0x0 0 > r17 0x0 0 > r18 0x0 0 > r19 0x0 0 > r20 0x0 0 > r21 0x0 0 > r22 0x0 0 > r23 0x64 100 > r24 0x5 5 > r25 0x1002d438 268620856 > r26 0x1002d9f0 268622320 > r27 0x1002c578 268617080 > r28 0x1 1 > r29 0x10031000 268636160 > r30 0xffbf7d0 268171216 > r31 0x1002d9f0 268622320 > pc 0xfef2058 267329624 > ps 0xd032 53298 > cr 0x24044022 604258338 > lr 0xfef2054 267329620 > ctr 0xfccefa0 265088928 > xer 0x20000000 536870912 > fpscr 0x0 0 > vscr 0x0 0 > vrsave 0x0 0 >=20 > (gdb) p/x $pc > $1 =3D 0xfef2058 >=20 > 0x0fef2058 <BN_bn2dec+472>: stw r3,0(r29) >=20 > (gdb) x 0x10031000 > 0x10031000: Cannot access memory at address 0x10031000 >=20 >=20 >=20 >=20 >=20 >=20 >=20 >=20 >=20 >=20 > On 7/5/05, David Ho <davidkwho@gmail.com> wrote: > > 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 <cmurch@mrv.com> > > Date: Jul 1, 2005 9:46 AM > > Subject: RE: PPC bn_div_words routine rewrite > > To: David Ho <davidkwho@gmail.com> > > > > > > David, > > I had observed the same issue on ppc 8xx machines after upgrading to th= e asm > > 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 sim= iliar > > 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 <davidkwho@gmail.com> 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 othe= r > > > 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_carr= y > > > 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 > > > ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: PPC bn_div_words routine rewrite 2005-07-05 17:01 ` David Ho @ 2005-07-05 20:21 ` David Ho 2005-07-05 21:22 ` Andy Polyakov 2005-07-05 21:25 ` David Ho 0 siblings, 2 replies; 10+ messages in thread From: David Ho @ 2005-07-05 20:21 UTC (permalink / raw) To: appro, linuxppc-embedded, openssl-dev Let's take first call to BN_div_word for example from BN_bn2dec, the parameter being passed to BN_div_word is (a=3D35, w=3D1000000000) (decimal numbers). It then calls the bn_div_words with (h=3D0, l=3D35, d=3D1000000000) if you examine the code in linux_ppc32.s it will exit early on because h is 0. the routine returns a divide by 0, which is undefined according to the manual. In the case of ppc8xx the result is 0x80000000. So this is the return value from bn_div_words, as seen in register R3. So what happens next is BN_div_word modifies "a" (1st parameter) with the result (0x80000000) and returns 23 as the remainder of the division. So "a" is never zero as a result and hence the test for BN_is_zero is always false. The problem fails the very first time it uses bn_div_words. The next thing I did naturally was to fix the case when you have h=3D0, which you can quite easy do it with the native divwu instruction. Lo and behold I was once again disappointed when h is not equal to 0. More to come... On 7/5/05, David Ho <davidkwho@gmail.com> wrote: > I can tell you with certainty, with reference to the function > BN_bn2dec, that since lp is a pointer, and within the while loop > around bn_print.c:136 lp is being incremented. Because the test > BN_is_zero(t) is always false, you have a pointer that is going off > into the stratosphere, hence the segfault on ppc8xx. >=20 > More analysis to come. >=20 > On 7/5/05, David Ho <davidkwho@gmail.com> wrote: > > First pass debugging results from gdb on ppc8xx. Executing ssh-keygen > > with following arguments. > > > > (gdb) show args > > Argument list to give program being debugged when it is started is > > "-t rsa1 -f /etc/ssh/ssh_host_key -N """. > > > > Program received signal SIGSEGV, Segmentation fault. > > BN_bn2dec (a=3D0x1002d9f0) at bn_print.c:136 > > 136 *lp=3DBN_div_word(t,BN_DEC_CONV); > > > > (gdb) i r > > r0 0x0 0 > > r1 0x7fffd580 2147472768 > > r2 0x30012868 805382248 > > r3 0x80000000 2147483648 > > r4 0xfef33fc 267334652 > > r5 0x25 37 > > r6 0xfccdef8 265084664 > > r7 0x7fffd4c0 2147472576 > > r8 0xfbad2887 4222429319 > > r9 0x84044022 2214871074 > > r10 0x0 0 > > r11 0x2 2 > > r12 0xfef2054 267329620 > > r13 0x10030bc8 268635080 > > r14 0x0 0 > > r15 0x0 0 > > r16 0x0 0 > > r17 0x0 0 > > r18 0x0 0 > > r19 0x0 0 > > r20 0x0 0 > > r21 0x0 0 > > r22 0x0 0 > > r23 0x64 100 > > r24 0x5 5 > > r25 0x1002d438 268620856 > > r26 0x1002d9f0 268622320 > > r27 0x1002c578 268617080 > > r28 0x1 1 > > r29 0x10031000 268636160 > > r30 0xffbf7d0 268171216 > > r31 0x1002d9f0 268622320 > > pc 0xfef2058 267329624 > > ps 0xd032 53298 > > cr 0x24044022 604258338 > > lr 0xfef2054 267329620 > > ctr 0xfccefa0 265088928 > > xer 0x20000000 536870912 > > fpscr 0x0 0 > > vscr 0x0 0 > > vrsave 0x0 0 > > > > (gdb) p/x $pc > > $1 =3D 0xfef2058 > > > > 0x0fef2058 <BN_bn2dec+472>: stw r3,0(r29) > > > > (gdb) x 0x10031000 > > 0x10031000: Cannot access memory at address 0x10031000 > > > > > > > > > > > > > > > > > > > > > > On 7/5/05, David Ho <davidkwho@gmail.com> wrote: > > > 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 <cmurch@mrv.com> > > > Date: Jul 1, 2005 9:46 AM > > > Subject: RE: PPC bn_div_words routine rewrite > > > To: David Ho <davidkwho@gmail.com> > > > > > > > > > David, > > > I had observed the same issue on ppc 8xx machines after upgrading to = the asm > > > version of the BN routines. Thank you very much for your work for th= e 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 s= imiliar > > > 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, i= s > > > 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 <davidkwho@gmail.com> 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 ot= her > > > > routines are hand-crafted, whereas this routine is compiled from a = C > > > > function that apparently has not gone through a whole lot of testin= g. > > > > > > > > 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 openss= l > > > > 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_ca= rry > > > > 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 > > > > > > ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: PPC bn_div_words routine rewrite 2005-07-05 20:21 ` David Ho @ 2005-07-05 21:22 ` Andy Polyakov 2005-07-05 21:25 ` David Ho 1 sibling, 0 replies; 10+ messages in thread From: Andy Polyakov @ 2005-07-05 21:22 UTC (permalink / raw) To: openssl-dev; +Cc: linuxppc-embedded > Let's take first call to BN_div_word for example from BN_bn2dec, the > parameter being passed to BN_div_word is (a=35, w=1000000000) (decimal > numbers). It then calls the bn_div_words with (h=0, l=35, > d=1000000000) if you examine the code in linux_ppc32.s it will exit > early on because h is 0. the routine returns a divide by 0, which is > undefined according to the manual. In the case of ppc8xx the result > is 0x80000000. And on the PPC machine I have access to it returns 0. This is explanation why I never experienced any SEGV, but a sparse decimal output. And it does explain why BN_is_zero condition never met on your system and you hit sbrk(0) limit and suffer the penalty. However! Note that updated routine, http://cvs.openssl.org/getfile/openssl/crypto/bn/asm/ppc.pl?v=1.4 never issues divide by 0 [it traps instead, but the condition is never met now when called from BN_div_words] and it does return correct answer to me. Can you really confirm that updated subroutine doesn't work for you? And if so, how does problem manifest? Still SEGV? At same point? It should pointed out that bug in ppc.pl is encountered only in 0.9.7 context, as 0.9.8 avoids it by normalizing divisor [and adjusting dividend accordingly]. BTW, I can confirm that 0.9.7 produces correct decimal ASCII with your routine [but no luck with make test_bn], but in 0.9.8 context decimal printout comes out truncated [not sparse with some significant digits there and there, but truncated] if your routine is pasted in. A. ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: PPC bn_div_words routine rewrite 2005-07-05 20:21 ` David Ho 2005-07-05 21:22 ` Andy Polyakov @ 2005-07-05 21:25 ` David Ho 2005-07-05 21:49 ` Andy Polyakov 1 sibling, 1 reply; 10+ messages in thread From: David Ho @ 2005-07-05 21:25 UTC (permalink / raw) To: appro, linuxppc-embedded, openssl-dev Okay, having actually did what Andy suggested, i.e. the one liner fix in the assembly code, bn_div_words returns the correct results. At this point, my conclusion is, up to openssl-0.9.8-beta6, the ppc32 bn_div_words routine generated from crypto/bn/ppc.pl is still busted.=20 Your solution is either to use the one liner fix andy provided in his reply or my routine. My solution is a complete rewrite of the routine, which is tested to work on ppc8xx. I personally do not know why it would not work on other ppc32 systems but if you have time to spare you are welcome to give it a try on your ppc32, because it is by far the most straight-forward algorithm for division. If you have done long division on paper from your primary school days, this function mimics exactly the long division steps in binary (as opposed to decimal). Way easier to fix if you know what the algorithm is trying to do. Comments I have for the old routine are: Why do you signal an overflow condition when it appears functions that call bn_div_words do not check for overflow conditions? That's why in my routine I just let the register overflow. Why the complexity, does it offer performance advantage? Obviously code size is huge compared to mine. David On 7/5/05, David Ho <davidkwho@gmail.com> wrote: > Let's take first call to BN_div_word for example from BN_bn2dec, the > parameter being passed to BN_div_word is (a=3D35, w=3D1000000000) (decima= l > numbers). It then calls the bn_div_words with (h=3D0, l=3D35, > d=3D1000000000) if you examine the code in linux_ppc32.s it will exit > early on because h is 0. the routine returns a divide by 0, which is > undefined according to the manual. In the case of ppc8xx the result > is 0x80000000. So this is the return value from bn_div_words, as seen > in register R3. >=20 > So what happens next is BN_div_word modifies "a" (1st parameter) with > the result (0x80000000) and returns 23 as the remainder of the > division. So "a" is never zero as a result and hence the test for > BN_is_zero is always false. The problem fails the very first time it > uses bn_div_words. >=20 > The next thing I did naturally was to fix the case when you have h=3D0, > which you can quite easy do it with the native divwu instruction. Lo > and behold I was once again disappointed when h is not equal to 0. >=20 > More to come... >=20 >=20 > On 7/5/05, David Ho <davidkwho@gmail.com> wrote: > > I can tell you with certainty, with reference to the function > > BN_bn2dec, that since lp is a pointer, and within the while loop > > around bn_print.c:136 lp is being incremented. Because the test > > BN_is_zero(t) is always false, you have a pointer that is going off > > into the stratosphere, hence the segfault on ppc8xx. > > > > More analysis to come. > > > > On 7/5/05, David Ho <davidkwho@gmail.com> wrote: > > > First pass debugging results from gdb on ppc8xx. Executing ssh-keyge= n > > > with following arguments. > > > > > > (gdb) show args > > > Argument list to give program being debugged when it is started is > > > "-t rsa1 -f /etc/ssh/ssh_host_key -N """. > > > > > > Program received signal SIGSEGV, Segmentation fault. > > > BN_bn2dec (a=3D0x1002d9f0) at bn_print.c:136 > > > 136 *lp=3DBN_div_word(t,BN_DEC_CONV); > > > > > > (gdb) i r > > > r0 0x0 0 > > > r1 0x7fffd580 2147472768 > > > r2 0x30012868 805382248 > > > r3 0x80000000 2147483648 > > > r4 0xfef33fc 267334652 > > > r5 0x25 37 > > > r6 0xfccdef8 265084664 > > > r7 0x7fffd4c0 2147472576 > > > r8 0xfbad2887 4222429319 > > > r9 0x84044022 2214871074 > > > r10 0x0 0 > > > r11 0x2 2 > > > r12 0xfef2054 267329620 > > > r13 0x10030bc8 268635080 > > > r14 0x0 0 > > > r15 0x0 0 > > > r16 0x0 0 > > > r17 0x0 0 > > > r18 0x0 0 > > > r19 0x0 0 > > > r20 0x0 0 > > > r21 0x0 0 > > > r22 0x0 0 > > > r23 0x64 100 > > > r24 0x5 5 > > > r25 0x1002d438 268620856 > > > r26 0x1002d9f0 268622320 > > > r27 0x1002c578 268617080 > > > r28 0x1 1 > > > r29 0x10031000 268636160 > > > r30 0xffbf7d0 268171216 > > > r31 0x1002d9f0 268622320 > > > pc 0xfef2058 267329624 > > > ps 0xd032 53298 > > > cr 0x24044022 604258338 > > > lr 0xfef2054 267329620 > > > ctr 0xfccefa0 265088928 > > > xer 0x20000000 536870912 > > > fpscr 0x0 0 > > > vscr 0x0 0 > > > vrsave 0x0 0 > > > > > > (gdb) p/x $pc > > > $1 =3D 0xfef2058 > > > > > > 0x0fef2058 <BN_bn2dec+472>: stw r3,0(r29) > > > > > > (gdb) x 0x10031000 > > > 0x10031000: Cannot access memory at address 0x10031000 > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On 7/5/05, David Ho <davidkwho@gmail.com> wrote: > > > > This is the second confirmed report of the same problem on the ppc8= xx. > > > > > > > > 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 <cmurch@mrv.com> > > > > Date: Jul 1, 2005 9:46 AM > > > > Subject: RE: PPC bn_div_words routine rewrite > > > > To: David Ho <davidkwho@gmail.com> > > > > > > > > > > > > David, > > > > I had observed the same issue on ppc 8xx machines after upgrading t= o the asm > > > > 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 pp= c BN > > > > routines after observing this issue or do you think they might have= similiar > > > > 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 ju= nk > > > > 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 asci= i > > > > decimal. > > > > > > > > Regards, > > > > David > > > > > > > > On 6/30/05, David Ho <davidkwho@gmail.com> wrote: > > > > > Hi all, > > > > > > > > > > This is a rewrite of the bn_div_words routine for the PowerPC arc= h, > > > > > tested on a MPC8xx processor. > > > > > I initially thought there is maybe a small mistake in the code th= at > > > > > 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 test= ing. > > > > > > > > > > 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 open= ssl > > > > > 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 > > > > > > > > > > ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: PPC bn_div_words routine rewrite 2005-07-05 21:25 ` David Ho @ 2005-07-05 21:49 ` Andy Polyakov 0 siblings, 0 replies; 10+ messages in thread From: Andy Polyakov @ 2005-07-05 21:49 UTC (permalink / raw) To: openssl-dev; +Cc: linuxppc-embedded > Okay, having actually did what Andy suggested, i.e. the one liner fix > in the assembly code, bn_div_words returns the correct results. Note that the final version, one committed to all relevant OpenSSL branches since couple of days ago and one which actually made to just released 0.9.8, is a bit different from originally suggested one-line fix, see for example http://cvs.openssl.org/chngview?cn=14199. > At this point, my conclusion is, up to openssl-0.9.8-beta6, the ppc32 > bn_div_words routine generated from crypto/bn/ppc.pl is still busted. Yes. Though it should be noted that 0.9.8 was inadvertently avoiding the bug condition. Recall that original problem report was for 0.9.7. > Why do you signal an overflow condition when it appears functions that > call bn_div_words do not check for overflow conditions? That's question to IBM. By the time they submitted the code, I've explicitly asked what would be appropriate way to generate *fatal* condition at that point, i.e. one which would result in a core dump, and it came out as division by 0 instruction. By that time I had no access to any PPC machine and had to just go with it. Now it actually came as surprise that division by 0 does not raise an exception, but silently returns implementation-specific value... A. ^ permalink raw reply [flat|nested] 10+ messages in thread
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2005-06-30 22:22 ` PPC bn_div_words routine rewrite David Ho
2005-07-01 17:36 ` Andy Polyakov
2005-07-04 14:35 ` David Ho
2005-07-05 15:00 ` Andy Polyakov
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2005-07-05 15:45 ` Fwd: " David Ho
2005-07-05 16:36 ` David Ho
2005-07-05 17:01 ` David Ho
2005-07-05 20:21 ` David Ho
2005-07-05 21:22 ` Andy Polyakov
2005-07-05 21:25 ` David Ho
2005-07-05 21:49 ` Andy Polyakov
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