This is a discussion on Re: PPC bn_div_words routine rewrite - Openssl ; > 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 ...
> 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
>>>>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
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!
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.
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