On Mon, Feb 13, 2017 at 06:08:52PM -0500, Jessica Yu wrote: > +++ Josh Poimboeuf [13/02/17 12:41 -0600]: > > On Mon, Feb 13, 2017 at 12:07:09AM -0800, Marc MERLIN wrote: > > > Hi Josh, > > > > > > I'll start with the story as to why. > > > i've lost more hours than I care to list, because I was unable to build > > > the virtualbox kernel driver with newer kernels. > > > Sadly, it gives no useful debug info outside of > > > make[1]: *** No rule to make target '/tmp/vbox.0/linux/SUPDrv-linux.o', > > > needed by '/tmp/vbox.0/vboxdrv.o'. Stop. > > > > > > It took some pretty deep debugging to finally see this: > > > Trying rule prerequisite 'tools/objtool/objtool'. > > > Looking for a rule with intermediate file 'tools/objtool/objtool'. > > > Avoiding implicit rule recursion. > > > which look quite inoccuous and don't look as errors at all. > > > When I filed a bug with the vbox folks, they were unable to find out why > > > the module refused to build on my kernel, and I was stuck with older > > > kernels as a result. > > > > > > Then, I had another module, bbswitch, to turn off the nvidia chip on my > > > laptop to save battery. That one also failed to build with newer > > > kernels, but thankfully made it more clear that the problem was related > > > to tools/objtool/objtool missing. > > > > > > But why was it missing? No idea... > > > I trace that down to CONFIG_STACK_VALIDATION which there seems to be no > > > menu option for, so I manually disable it in .config, rebuild, and it's > > > automatically re-enabled. Gah. > > > > Hm, that doesn't sound right. Nothing automatically enables > > CONFIG_STACK_VALIDATION. It should be disabled unless manually enabled. > > Maybe you got it confused with CONFIG_HAVE_STACK_VALIDATION, which is > > always enabled? > > > > BTW, there is a config option for it in the menu: > > > > Kernel hacking > > Compile-time checks and compiler options > > Compile-time stack metadata validation > > > > > More hair pulling, and finally I make a typo > > > saruman:/usr/src/linux-block# make xonfig > > > Makefile:1044: "Cannot use CONFIG_STACK_VALIDATION, please install > > > libelf-dev, libelf-devel or elfutils-libelf-devel" > > > scripts/kconfig/conf --silentoldconfig Kconfig > > > Makefile:1044: "Cannot use CONFIG_STACK_VALIDATION, please install > > > libelf-dev, libelf-devel or elfutils-libelf-devel" > > > make: *** No rule to make target 'xonfig'. Stop. > > > > > > Sure enough, this was my problem, but I never saw the error message > > > because I build kernels with > > > make-kpkg --revision 1gandalf kernel-image > > > which does other stuff and hid that warning, which really should have > > > been a fatal error in my opinion. > > > > > > Given that > > > 1) CONFIG_STACK_VALIDATION seems silently auto enabled. > > > 2) without libelf-dev, the kernel will build but will leave a tree > > > missing objtool, which in turn causes (all?) 3rd party modules to fail > > > building. > > > > Yes, this is a bug. > > > > > 3) and that it's kind of non trivial to find out why if that happens, > > > > > > Would you consider making > > > "Cannot use CONFIG_STACK_VALIDATION, please install libelf-dev, > > > libelf-devel or elfutils-libelf-devel" > > > a build error as opposed to a warning? > > > This sure would have saved me countless errors of debugging the wrong > > > things. > > > > Correct me if I'm wrong, but it sounds like make-kpkg suppressed stderr? > > If so, that should be fixed. > > > > When I try to build an OOT module with CONFIG_STACK_VALIDATION enabled > > and elfutils-libelf-devel missing (on Fedora), I get: > > > > make: Entering directory '/home/jpoimboe/git/linux' > > make[1]: Entering directory '/home/jpoimboe/ktest/output' > > CC [M] /home/jpoimboe/livepatch-test/1/livepatch2.o > > /bin/sh: ./tools/objtool/objtool: No such file or directory > > /home/jpoimboe/git/linux/scripts/Makefile.build:300: recipe for target > > '/home/jpoimboe/livepatch-test/1/livepatch2.o' failed > > make[2]: *** [/home/jpoimboe/livepatch-test/1/livepatch2.o] Error 1 > > /home/jpoimboe/git/linux/Makefile:1490: recipe for target > > '_module_/home/jpoimboe/livepatch-test/1' failed > > make[1]: *** [_module_/home/jpoimboe/livepatch-test/1] Error 2 > > make[1]: Leaving directory '/home/jpoimboe/ktest/output' > > Makefile:150: recipe for target 'sub-make' failed > > make: *** [sub-make] Error 2 > > make: Leaving directory '/home/jpoimboe/git/linux' > > > > It's not a perfect error message, but the > > > > '/bin/sh: ./tools/objtool/objtool: No such file or directory' > > > > is at least a big clue. I'm curious why you didn't see that. > > > > Anyway, the above libelf-dev warning is just a warning and not a build > > error because CONFIG_STACK_VALIDATION is enabled for allyesconfig, and > > it's not a severe enough problem to warrant breaking the build. > > > > Ideally the same warning should be printed when building OOT modules. > > I'll try to figure out if there's a way to do that it. > > Btw, it looks like the libelf warning is inside an `ifeq ($(KBUILD_EXTMOD),)` > block, so it does not get applied to OOT modules. It would be > possible to add the warning to the corresponding KBUILD_EXTMOD (else) > block or somewhere else in the Makefile common to both cases (probably > more preferable). I tried the latter case and the warning prints for > all cases (vmlinux, intree, external modules).
Aha, that explains it, thanks. Will look into fixing it. -- Josh
