On Wed, Sep 11, 2024 at 12:39:42AM -0700, Josh Poimboeuf wrote: > On Mon, Sep 02, 2024 at 08:59:43PM -0700, Josh Poimboeuf wrote: > > Hi, > > > > Here's a new way to build livepatch modules called klp-build. > > > > I started working on it when I realized that objtool already does 99% of > > the work needed for detecting function changes. > > > > This is similar in concept to kpatch-build, but the implementation is > > much cleaner. > > > > Personally I still have reservations about the "source-based" approach > > (klp-convert and friends), including the fragility and performance > > concerns of -flive-patching. I would submit that klp-build might be > > considered the "official" way to make livepatch modules. > > > > Please try it out and let me know what you think. Based on v6.10. > > > > Also avaiable at: > > > > git://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git klp-build-rfc > > Here's an updated branch with a bunch of fixes. It's still incompatible > with BTF at the moment, otherwise it should (hopefully) fix the rest of > the issues reported so far. > > While the known bugs are fixed, I haven't finished processing all the > review comments yet. Once that happens I'll post a proper v2. > > git://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git klp-build-v1.5 Hi Josh, I've had much better results with v1.5, thanks for collecting up those fixes in a branch. One new thing to report: depending on the optimzation of drivers/gpu/drm/vmwgfx/vmwgfx.o, objtool may throw a complaint about an unexpected relocation symbol type: $ make -j$(nproc) drivers/gpu/drm/vmwgfx/vmwgfx.o drivers/gpu/drm/vmwgfx/vmwgfx.o: error: objtool [check.c:1048]: unexpected relocation symbol type in .rela.discard.func_stack_frame_non_standard: 0 I modified check.c to print the reloc->sym->name in this case and it reports, "vmw_recv_msg". If I recreate vmwgfx.o and dump the symbol table, I notice that this is a NOTYPE symbol (probably because of vmw_recv_msg.constprop.0?) $ ld -m elf_x86_64 -z noexecstack -r -o drivers/gpu/drm/vmwgfx/vmwgfx.o @drivers/gpu/drm/vmwgfx/vmwgfx.mod $ readelf --wide --symbols drivers/gpu/drm/vmwgfx/vmwgfx.o | grep -b -e 'vmw_recv_msg' -e 'vmw_send_msg' 148334: 2198: 0000000000000010 183 FUNC LOCAL DEFAULT 1255 vmw_send_msg 151116: 2234: 0000000000000010 409 FUNC LOCAL DEFAULT 1251 vmw_recv_msg.constprop.0 180895: 2615: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND vmw_recv_msg I don't think the config matters (I used the centos-stream-10 config) as long as the driver builds. I only saw this with a rhel-9 gcc version 11.5.0 20240719 (Red Hat 11.5.0-2) and not fedora gcc version 12.3.1 20230508 (Red Hat 12.3.1-1), which kept vmw_recv_msg w/o constprop. -- Joe
