> > The introduced header file linux/version.h in libbpf_probes.c may have a > > wrong macro KERNEL_VERSION for calculating LINUX_VERSION_CODE in some old > > kernel (Debian9, 10). Below is a version info example from Debian 10. > > > > release: 4.19.0-22-amd64 > > version: #1 SMP Debian 4.19.260-1 (2022-09-29) > > > > The macro KERNEL_VERSION is defined to (((a) << 16) + ((b) << 8)) + (c)), > > which a, b, and c stand for major, minor and patch version. So in example here, > > the major is 4, minor is 19, patch is 260, the LINUX_VERSION(4, 19, 260) which > > is 267268 should be matched to LINUX_VERSION_CODE. However, the KERNEL_VERSION_CODE > > in linux/version.h is defined to 267263. > > > > I noticed that the macro KERNEL_VERSION in linux/version.h of some new kernel is > > defined to (((a) << 16) + ((b) << 8) + ((c) > 255 ? 255 : (c))). And > > KERNEL_VERSION(4, 19, 260) is equal to 267263 which is the right LINUX_VERSION_CODE. > > > > The mismatched LINUX_VERSION_CODE which will cause failing to load kprobe BPF > > programs in the version check of BPF syscall. > > > > The return value of get_kernel_version in libbpf_probes.c should be matched to > > LINUX_VERSION_CODE by correcting the macro KERNEL_VERSION. > > > > Signed-off-by: songrui.771 <songrui.771@xxxxxxxxxxxxx> > > This needs to be your name, not your email alias (do you use ".771" as a > name to sign things with?) Thanks for your reminding. I will change it. > > > --- > > tools/lib/bpf/libbpf_probes.c | 10 +++++++--- > > 1 file changed, 7 insertions(+), 3 deletions(-) > > > > diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c > > index 4f3bc968ff8e..5b22a880c7e7 100644 > > --- a/tools/lib/bpf/libbpf_probes.c > > +++ b/tools/lib/bpf/libbpf_probes.c > > @@ -18,6 +18,10 @@ > > #include "libbpf.h" > > #include "libbpf_internal.h" > > > > +#ifndef LIBBPF_KERNEL_VERSION > > +#define LIBBPF_KERNEL_VERSION(a, b, c) (((a) << 16) + ((b) << 8) + ((c) > 255 ? 255 : (c))) > > +#endif > > What is wrong with using the KERNEL_VERSION() macro, it should be fixed > to work properly here, right? Did we not get this resolved in the > main portion of the kernel already? The KERNEL_VERSION() macro from linux/version.h is wrong in some old kernel(Debian 9, 10) that we would like to support. As you said, the problem was resolved in the newer kernel. Here is the difference: linux/version.h in older kernel: #define KERNEL_VERSION(a, b, c) (((a) << 16) + ((b) << 8)) + (c))) in newer kernel: #define KERNEL_VERSION(a, b, c) KERNEL_VERSION(a, b, c) (((a) << 16) + ((b) << 8) + ((c) > 255 ? 255 : (c))) Using the KERNEL_VERSION macro in the older kernel returns the kern version which is mismatched to the LINUX_VERSION_CODE that will cause failing to load the BPF kprobe program. In my opinion, it is a more generic solution that corrects the KERNEL_VERSION() macro in libbpf to support some old kernel. Hope I make that clear. Thanks. Jerry Song
