On Sat, Oct 23, 2021 at 5:05 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote: > > hi, > I'm trying to enable BTF for kernel module in fedora, > and I'm getting big increase on modules sizes on s390x arch. > > Size of modules in total - kernel dir under /lib/modules/VER/ > from kernel-core and kernel-module packages: > > current new > aarch64 60M 76M > ppc64le 53M 66M > s390x 21M 41M > x86_64 64M 79M > > The reason for higher increase on s390x was that dedup algorithm > did not detect some of the big kernel structs like 'struct module', > so they are duplicated in the kernel module BTF data. The s390x > has many small modules that increased significantly in size because > of that even after compression. > > First issues was that the '--btf_gen_floats' option is not passed > to pahole for kernel module BTF generation. > > The other problem is more tricky and is the reason why this patchset > is RFC ;-) > > The s390x compiler generates multiple definitions of the same struct > and dedup algorithm does not seem to handle this at the moment. > > I put the debuginfo and btf dump of the s390x pnet.ko module in here: > http://people.redhat.com/~jolsa/kmodbtf/ > > Please let me know if you'd like to see other info/files. > Hard to tell what's going on without vmlinux itself. Can you upload a corresponding kernel image with BTF in it? > I found code in dedup that seems to handle such situation for arrays, > and added 'some' fix for structs. With that change I can no longer > see vmlinux's structs in kernel module BTF data, but I have no idea > if that breaks anything else. > > thoughts? thanks, > jirka > > > --- > Jiri Olsa (2): > kbuild: Unify options for BTF generation for vmlinux and modules > bpf: Add support to detect and dedup instances of same structs > > Makefile | 3 +++ > scripts/Makefile.modfinal | 2 +- > scripts/link-vmlinux.sh | 11 +---------- > scripts/pahole-flags.sh | 20 ++++++++++++++++++++ > tools/lib/bpf/btf.c | 12 ++++++++++-- > 5 files changed, 35 insertions(+), 13 deletions(-) > create mode 100755 scripts/pahole-flags.sh >
