I think I now understand. The Makefile indeed seems to fail to correctly rebuild when a header has changed.
As the performance branch has removed the 'int bigendian' from SHA1_CTX in lib/sha1.h, the perf-branch and master-branch are binary incompatible. So the command-line utility does not get fully recompiled and instead of the value of found_collision will read a different value of SHA1_CTX. So be careful to always do a 'make clean' for now. -- Marc ----- Original Message ----- From: "Jeff King" <p...@peff.net> To: "Marc Stevens" <marc.stev...@cwi.nl> Cc: "Linus Torvalds" <torva...@linux-foundation.org>, "Dan Shumow" <dan...@microsoft.com>, "Junio C Hamano" <gits...@pobox.com>, "Git Mailing List" <git@vger.kernel.org> Sent: Monday, March 13, 2017 10:00:23 PM Subject: Re: [PATCH] Put sha1dc on a diet On Mon, Mar 13, 2017 at 09:47:54PM +0100, Marc Stevens wrote: > Linus: > I would be surprised, the dependencies should be automatically determined. > > BTW Did you make local changes to this perf branch? I can reproduce it with: cd sha1collisiondetection git clean -dqfx ;# make sure we are starting from scratch git checkout 9c8e73cadb35776d3310e3f8ceda7183fa75a39f make bin/sha1dcsum $file git checkout 55d1db0980501e582f6cd103a04f493995b1df78 make bin/sha1dcsum $file The final call to sha1dcsum will report a collision, even though the first one did not. It also reproduces with the original snippet I posted. I didn't notice because I was just collecting the timings then (and I originally noticed the problem on the versions I had pulled into Git, where it works as expected; but then I am just pulling in the two source files, without all of the libtool magic). -Peff
