Date: Sun, 6 Jan 2013 02:38:07 +0100 From: magnum <john.magnum@...hmail.com> To: john-dev@...ts.openwall.com Subject: Re: New plugin load order magic On 5 Jan, 2013, at 11:58 , Frank Dittrich <frank_dittrich@...mail.com> wrote: > On 01/05/2013 10:52 AM, magnum wrote: >> On 5 Jan, 2013, at 2:34 , Frank Dittrich <frank_dittrich@...mail.com> wrote: >>> When I change the Makefile again (use $(SORT) without -r), remove >>> john.o, and build a new john version without a make clean, I get a >>> binary of size of 2146816 bytes. >>> The dummy format test gives between 62825K and 64214K now, which is >>> somewhere between the c/s rates of the other binaries. >>> >>> Admittedly, dummy isn't the most important format. >>> But I don't understand these fairly reproducible c/s rate differences. >>> And I really don't know why the binaries differ in size. >>> >>> May be I should get some sleep and hope someone else can come up with an >>> explanation. >> >> Both issues are just effects of building slightly different things. The size difference is due to alignments. > > Not really. When I use > $ make clean > before building the version with the reversed sort sequence, the binary > gets the same size as the one with the normal sort sequence. > > Only if instead of a > $ make clean > I just remove those objects which should be affected by the different > sort order (../run/john, john.o, fmt_externs.h, fmt_registers.h), > the binary which results from the build differs in size. I really appreciate your testing, but this is a fairly weird report and I can't think of any other response than just ignore it. What conclusion should I draw from this? What conclusion do you draw yourself? >> The speed difference, we have seen that before. Sometimes I have even made optmizations that I could "prove" (with valgrind) should speed things up, yet slowed things down. This may be because of bad luck with cache lines, and things like that. > > You are probably right. But I dislike this unsatisfying degree of > predictability. I do too, really, but from benchmarking dummy 10 times in a row with any build I usually get that variation in speed. This is frustrating and I have spent some time in the past trying to mitigate it. Some other formats produce the same speed, down to the last digit, every time. I have absolutely no idea why! My punch line is that I presume your observations are correct - but they are not really results of the changes to the plugin magic. magnum
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