On Tue, Apr 28, 2020 at 04:40:47PM -0600, Simon Glass wrote: > Hi Tom, > > On Tue, 28 Apr 2020 at 09:52, Tom Rini <[email protected]> wrote: > > > > On Tue, Apr 28, 2020 at 09:41:14AM -0600, Simon Glass wrote: > > > Hi Tom. > > > > > > On Tue, 28 Apr 2020 at 08:19, Tom Rini <[email protected]> wrote: > > > > > > > > On Mon, Apr 27, 2020 at 04:10:06PM -0700, Vagrant Cascadian wrote: > > > > > On 2020-04-27, Simon Glass wrote: > > > > > > On Sun, 26 Apr 2020 at 18:58, Heinrich Schuchardt > > > > > > <[email protected]> wrote: > > > > > >> > > > > > >> Am April 27, 2020 12:29:29 AM UTC schrieb Simon Glass > > > > > >> <[email protected]>: > > > > > >> >At present U-Boot always builds dtc if CONFIG_OF_CONTROL is > > > > > >> >defined. > > > > > >> >This > > > > > >> >is wasteful when the system already has a suitable version > > > > > >> >available. > > > > > >> > > > > > > >> >Update the Makefile logic to build dtc only if the version > > > > > >> >available is > > > > > >> >too old. > > > > > >> > > > > > > >> >This saves about 2.5 seconds of elapsed time on a clean build for > > > > > >> >me. > > > > > >> > > > > > > >> >- Add a patch to bring back the dtc-version.sh script > > > > > >> >- Update the check to make sure libfdt is available if needed > > > > > >> > > > > > >> U -Boot has been set up to create reproducible builds. With this > > > > > >> patch dtc will have to be made a build dependency to provide > > > > > >> reproducibility. Cf. > > > > > >> https://www.debian.org/doc/debian-policy/ch-source.html#reproducibility > > > > > >> > > > > > >> This may require changes in the packaging of U-Boot in Linux > > > > > >> distributions. Nothing to stop this patch, just something to keep > > > > > >> in > > > > > >> mind. > > > > > >> > > > > > >> You presume that future versions of dtc will always be backward > > > > > >> compatible with U-Boot. Ok, we do the same for other tools like gcc > > > > > >> too (with surprises at each new major release). > > > > > > > > > > In general when packaging for Debian, the preference is to not use > > > > > embedded code copies if at all possible. This does require paying > > > > > attention to backwards and forwards compatibility issues a bit. > > > > > > > > > > A simple example: The security team in Debian generally likes to fix a > > > > > problem in a single source package, rather than an arbitrary number of > > > > > source packages that happen to share some embedded copy of the code > > > > > from > > > > > who knows when... > > > > > > > > > > So at least from my perspective, I'd be happy to use the Debian > > > > > packaged > > > > > dtc (a.k.a. device-tree-compiler), rather than the one embedded in > > > > > u-boot sources. > > > > > > > > > > Silently switching to the embedded copy sounds a little scary; I would > > > > > prefer for that to be explicit... a build flag to specify one way or > > > > > the > > > > > other and failing is better that being too clever about autodetecting. > > > > > > > > > > > > > > > > Should we disable this check (and always build dtc) when doing a > > > > > > repeatable build? Is that SOURCE_DATE_EPOCH? > > > > > > > > > > And with my Reproducible Builds hat on, builds would ideally *always* > > > > > be > > > > > reproducible, given the same sources and toolchain... several > > > > > distributions and software projects provide information sufficient to > > > > > reproduce the build environment: > > > > > > > > > > https://reproducible-builds.org/docs/recording/ > > > > > > > > > > > > > > > While SOURCE_DATE_EPOCH is definitely one sign that the builder is > > > > > explicitly attempting to be reproducible; It's a bit of a kludge to > > > > > try > > > > > and be more reproducible just because SOURCE_DATE_EPOCH is > > > > > set. SOURCE_DATE_EPOCH should really only affect the behavior of date > > > > > or > > > > > time related things; even better would be to not embded time related > > > > > > > > This is probably one of those cases where we should just continue to act > > > > like the linux kernel and always use and build our own copy of dtc. > > > > Then, when someone convinces the kernel folks to change their ways, we > > > > can adopt that. > > > > > > It seems that Vagrant wants to use the system dtc by default and > > > require an explicit option to use the in-built dtc. I don't think that > > > would work well for most users though. > > > > Right, and this is where I disagree and point to the kernel. Get that > > changed first. > > > > > It is in my view somewhat mad to build dtc for every one of 1400 > > > boards as I do today when running buildman. > > > > This is a different funny case. Perhaps ccache could be helpful here? > > I think the way it's used in OpenEmbedded, such that you have a cache > > that's more local to what's building vs global cache, could be helpful > > here too. A ccache instance per CI job / world build could help. A > > flag to buildman to support that could help, yes? Thanks! > > So not allow using the system dtc? Or are you OK with a build option?
I'd rather not have a build option as that's going to encourage people to use it, and then that'll lead to problems down the line. > The thing is I would prefer to avoid another level of cache for a > problem that only exists because of our kernel design decision. > > As to changing the kernel, I cannot imagine that happening as they > change dtc all the time. We really need to stay better in sync with the kernel here too. Trying to get more syncs of kbuild/kconfig/dtc/etc with kernel releases is on my list. -- Tom
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