On Sun, Dec 13, 2020 at 03:36:58PM -0800, Chris Marusich wrote: > Hi, > > I tried to do some experiments to see if this problem happens with the > current GCC (version 10). > > I built GCC 10 (not cross-compiling) on an x86_64 system using Guix with > substitutes on Debian. (I tried without substitutes, too, but some of > the dependencies failed to be built for unrelated reasons.) I then > manually copied the /gnu/store and related files (except for the GCC 10 > output paths) from Debian onto a Fedora machine, and I rebuilt GCC 10 > there using Guix (again, not cross-compiling). The output on Fedora was > identical to that of Debian. Of course, the configuration Guix uses to > build GCC 10 is a bit different from the one used to (cross-)build the > powerpc64-linux bootstrap GCC, but it's still an interesting data point. > In particular, GCC 10's libstdc++.a was identical on Debian and Fedora, > so I suppose maybe they've fixed that issue in the more recent versions. > > I also tried to use Guix (the current version, from master branch - I > ran guix pull today) to cross-build gcc-10 for the powerpc64-linux-gnu > target on both Debian and Fedora x86_64 systems, starting from scratch > with substitutes enabled: > > guix build --target=powerpc64-linux-gnu -e '(@ (gnu packages gcc) gcc-10)' > > On both Debian and Fedora, the build of gcc-10.2.0.drv failed with the > following error: > > checking for -fPIC -shared... yes > configure: error: > Building GCC with plugin support requires a host that supports > -fPIC, -shared, -ldl and -rdynamic. > > This basically just means that we can't cross-build gcc-10 for > powerpc64-linux-gnu out of the box on x86_64 with current Guix. I was > hoping that the builds would succeed, and I would be able to find out if > cross-building gcc-10 in this way would create non-reproducible > artifacts. I was hoping maybe I could ask for help from the GCC > community if that were the case. But since it doesn't even build, the > results of that experiment were not very useful. > > It's been almost half a year now, and we're not really any closer to > figuring out why the cross-built GCC bootstrap binary is > non-reproducible. It seems counter-productive to obsess about making > this specific binary reproducible, although I wish it could be so. > > What do you think about using the bootstrap binaries we built half a > year ago, and proceed with bootstrapping efforts? To be totally honest, > I'm feeling pretty exhausted by this bug, since I have spent so many > days trying to unravel it, and I haven't made any significant progress. > With no clear end in sight, I would really prefer to move on instead of > blocking the entire bootstrapping effort on this reproducibility bug. > The reproducibility of the bootstrap binaries is important, but simply > having any bootstrap binaries at all is also important. I think I have > done my due diligence to try making them reproducible. Most of them > are, but I just can't figure out why GCC isn't. I think it would be > best to proceed with the binaries we have. > > Ludovic Courtès writes: > > > Hi Chris, > > > > Chris Marusich skribis: > > > >> From e3d1778a86dfd171d59d91eb01417faaf63dfa17 Mon Sep 17 00:00:00 2001 > >> From: Chris Marusich > >> Date: Sat, 19 Sep 2020 14:25:43 -0700 > >> Subject: [PATCH] gnu: Disable libstdc++ in bootstrap GCC. > >> > >> Fixes part of: . > >> > >> * gnu/packages/make-bootstrap.scm (%gcc-static) [#:configure-flags]: Add > >> --disable-libstdcxx to disable building the libstdc++-v3 directory. > > > > [...] > > > >> + ;; In this GCC version, libstdc++.a is not reproducible: > >> + ;; https://debbugs.gnu.org/cgi/bugreport.cgi?bug=41669 > >> + "--disable-libstdcxx" > > > > Does it have any effect with GCC > 4.7? My understanding is that it > > builds its libstdc++ no matter what. > > > > Also, if it’s just libstdc++.a that’s problematic (ordering issue in the > > .a archive?), perhaps we can use --disable-shared? > > > > My 2¢ (I didn’t follow the whole discussion), > > Ludo’. > > Actually, --disable-shared is already present in the configure options. > My understanding is that libstdc++.a is a statically linked library > (perhaps I am mistaken...?), so I don't see why the presence or absence > of --disable-shared would affect it. I thought that option was just > supposed to control whether or not to build shared libraries. > > Efraim Flashner writes: > > > On Fri, Sep 25, 2020 at 11:52:48PM -0700, Chris Marusich wrote: > >> Hi everyone, > >> > >> Efraim Flashner writes: > >> > >> > Is this a file we actually need during the bootstrap process? Can we > >> > "work around it" by just deleting it? > > I've spent all of my spare Guix time trying to debug this > reproducibility issue first, and half a year has passed without progress > as a result. I think we should use the bootstrap binaries we built half > a year ago, and move on with life. > > At this point, it might even make more sense to try bootstrapping for > powerpc64le instead of powerpc64, since the rest of the world seems to > be gravitating toward the little-endian variant on POWER9 hardware, and > thus various programs out there are more likely to be better tested on > powerpc64le than powerpc64. > > In any case, I don't think we should wait any longer. As far as powerpc64 vs powerpc64le, I'll let those with the hardware have more of a say, they'll be the ones using it. As far as the bootstrap binaries go, I don't remember having this much pushback with my binaries for aarch64 (just a request to rebuild with guile-2.0.14 since it was reproducible), and I'm not sure how much Janneke had with the Hurd binaries but I don't think it was this much. The ultimate goal anyway is to replace them with artisanally crafted mes binaries, and I understand we want to have them as reproducible as possible, but I don't think it's fair to keep this architecture out when we've let other ones in with similar reproducible problems. -- Efraim Flashner אפרים פלשנר GPG key = A28B F40C 3E55 1372 662D 14F7 41AA E7DC CA3D 8351 Confidentiality cannot be guaranteed on emails sent or received unencrypted