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.
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