On Sat, Mar 2, 2019 at 3:03 AM Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> wrote: > > On Fri, Mar 01, 2019 at 03:25:05PM +0900, Masahiro Yamada wrote: > [...] > > > > I am guessing the user will run these commands > > > > on the target system. > > > > In other words, external modules are native-compiled. > > > > So, > > > > > > > > target-arch: arm64 > > > > host-arch: arm64 > > > > > > > > > > > > Is this correct? > > > > > > > > > > > > If I understood the assumed use-case correctly, > > > > kheaders.tar.xw will contain host-programs compiled for x86, > > > > which will not work on the target system. > > > > > > > > > > You are right, the above commands in the commit message work only if the > > > host/target are same arch due to scripts. > > > > > > However we can build with arm64 device connected to a host, like this (which > > > I tested): > > > > > > adb shell modprobe kheaders; adb pull /proc/kheaders.tar.xz > > > rm -rf $HOME/headers; mkdir -p $HOME/headers > > > tar -xvf /proc/kheaders.tar.xz -C $HOME/headers >/dev/null > > > cd my-kernel-module > > > make -C $HOME/headers M=$(pwd) ARCH=arm64 CROSS_COMPILE=aarch64- modules > > > adb push test.ko /data/; adb shell rmmod kheaders > > > > > > The other way we can make this work is using x86 usermode emulation inside a > > > chroot on the Android device which will make the earlier commands work. One > > > thing to note is that Android also runs on x86 hardware so the commands in > > > the commit message will work even for x86 Android targets already. > > > > > > Also note that this the "module building" part is really only one of the > > > usecases. eBPF is another which needs the headers - and the headers are vast > > > majority of the archive. Headers take 3.1MB out of 3.6MB of the archive on > > > arm64 builds. > > > > > > How do you want to proceed here, should I mention these points in the commit > > > message? > > > > > > > > I do not request a re-spin just for a matter of commit log, > > but this version produces an empty tarball. > > So, you will have a chance to update the patch anyway. > > > > In the next version, it would be nice to note that > > "external modules must be built on the same host arch > > as built vmlinux". > > Ok, I respun it with 1 more minor nit for arm64 building. Please take a look. I have not checked code-diff in v3 yet. Anyway, I will add comments to v4 if I notice something. > > Let me ask one more question. > > > > I guess this patch is motivated by > > how difficult to convey kernel headers > > from vendors to users. > > > > In that situation, how will the user find > > the right compiler to use for building external modules? > > > > > > > > > > Greg KH said: > > > > We don't ever support the system of loading a module built with anything > > other than the _exact_ same compiler than the kernel was. > > > > > > For the full context, see this: > > https://lore.kernel.org/patchwork/patch/836247/#1031547 > > IMO this issue is not related to this patch but is just an issue with > building external modules in general. I do not think it is an issue of the build system, at least. As far as I understood Greg's comment, it is troublesome without the assumption that vmlinux and modules are built by the same compiler. It is related to this patch since this patch assumes use-cases where external modules are built in a completely different environment, where a different compiler is probably installed. > It is up to the user to use the right > compiler, etc. I will let Greg comment more on that. > thanks, > > - Joel > -- Best Regards Masahiro Yamada
