** Description changed: [Impact] When building out-of-tree kernel modules (via DKMS or manual module build), BTF (BPF Type Format) generation is skipped due to a vmlinux not being found in the expected location. This prevents BPF-based tracing tools (bpftrace, BCC) from attaching kprobes/kfuncs to out-of-tree module functions. [Fix] - The patch "UBUNTU: [Packaging] dbgsym: add vmlinux symlink to headers - directory" resolves this issue by including a stripped-down version of - the vmlinux with only .BTF and .BTF_ids sections at /usr/src/linux- - headers-7.0.0-xx-generic/vmlinux in the linux-headers-7.0.0-xx-<flavour> - packages. + The patch "UBUNTU: [Packaging] add stripped-down vmlinux with only BTF + sections to flavour headers package" resolves this issue by including a + stripped-down version of the vmlinux with only .BTF and .BTF_ids + sections at /usr/src/linux-headers-7.0.0-xx-generic/vmlinux in the + linux-headers-7.0.0-xx-<flavour> packages. This solution matches the one in Debian by Bastian Blank: https://salsa.debian.org/kernel-team/linux/-/commit/0dedced119aea5426f81a931 8c36e0a6c7339547. [Test Plan] Verify that BTF generation succeeds: 1. Install headers for the target kernel. $ sudo apt install linux-headers-7.0.0-xx-generic 2. Obtain sources for a test kernel module. $ git clone https://github.com/ivbakula/hello-world-kernel-module 3. Build this kernel module. make -C /lib/modules/7.0.0-xx-generic/build M=hello-world-kernel-module modules 4. Verify BTF generation is successful. $ objdump --section=.BTF -s ~/hello-world-kernel-module/hello.ko /root/hello-world-kernel-module/hello.ko: file format elf64-x86-64 Contents of section .BTF: 0000 9feb0100 18000000 00000000 60000000 ............`... 0010 60000000 16000000 00000000 0000000a `............... 0020 02000000 00000000 00000003 00000000 ................ 0030 03000000 01000000 05000000 00000000 ................ 0040 0000000a 04000000 15000000 0000000c ................ 0050 09000000 20000000 0000000c 08000000 .... ........... 0060 00000000 0000000d 01000000 00000000 ................ 0070 0000000d 00000000 68656c6c 6f5f6578 ........hello_ex 0080 69740068 656c6c6f 5f696e69 7400 it.hello_init. Note: if BTF generation is unsuccessful, the output will appear as: $ objdump --section=.BTF -s hello.nobtf.ko hello.nobtf.ko: file format elf64-x86-64 objdump: section '.BTF' mentioned in a -j option, but not found in any input file [Where issues could occur] This modifies the flavour-specific header package to include a stripped- down vmlinux with only .BTF and .BTF_ids sections. Issues could occur if software on the system assumes vmlinux at this path will be a full vmlinux, but finds the version with only .BTF and .BTF_ids sections. As a vmlinux file was not included in the headers at all before, it is unlikely existing functionality was relying on it. Original bug description: steps to reproduce: git clone https://github.com/ivbakula/hello-world-kernel-module $ cd hello-world-kernel-module $ make -C /usr/src/linux-headers-6.14.0-33-generic/ M=$PWD modules V=1 make: Entering directory '/usr/src/linux-headers-6.14.0-33-generic' <snip> # LD [M] hello.ko ld -r -m elf_x86_64 -z noexecstack --no-warn-rwx-segments --build- id=sha1 -T /usr/src/linux-headers-6.14.0-33-generic/scripts/module.lds -o hello.ko hello.o hello.mod.o .module-common.o # BTF [M] hello.ko if [ ! -f /usr/src/linux-headers-6.14.0-33-generic/vmlinux ]; then printf "Skipping BTF generation for %s due to unavailability of vmlinux\n" hello.ko 1>&2; else LLVM_OBJCOPY="objcopy" pahole -J --btf_gen_floats -j --skip_encoding_btf_inconsistent_proto --btf_gen_optimized --lang_exclude=rust --btf_base /usr/src/linux- headers-6.14.0-33-generic/vmlinux hello.ko; /usr/src/linux- headers-6.14.0-33-generic/tools/bpf/resolve_btfids/resolve_btfids -b /usr/src/linux-headers-6.14.0-33-generic/vmlinux hello.ko; fi; Skipping BTF generation for hello.ko due to unavailability of vmlinux make[1]: Leaving directory '/tmp/hello-world-kernel-module' make: Leaving directory '/usr/src/linux-headers-6.14.0-33-generic' "Skipping BTF generation for hello.ko due to unavailability of vmlinux" says vmlinux wasn't found. Workaround: ln -s /usr/lib/debug/boot/vmlinux-$(uname -r) /usr/src/linux-headers-$(uname -r)/vmlinux it seems to work.
-- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2133794 Title: BTF Generation Fails for Out-of-Tree Modules with Debuginfo Package To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2133794/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
