Messages in this thread | | | Date | Mon, 13 Feb 2017 18:08:52 -0500 | From | Jessica Yu <> | Subject | Re: Please turn "Cannot use CONFIG_STACK_VALIDATION" into build error |
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+++ 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).
Jessica
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