> > > > 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: > > But the kernels you want to "support" all have older kernel versions and > so you do not need the change to the macro as they are not running newer > kernel versions with an increased minor version number. > > So on those systems, building will work just fine, if not, then that's a > Debian bug and they should fix it in their kernel packages. > > 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. > > The KERNEL_VERSION() macro comes from the kernel you are building > against. And so that should match that kernel only. Thanks again for your reply. You're absolutely right. This bug exists on many older kernels(Debian9, 10, CentOS 7). It's not a kernel bug, but the kernel release package bug. I will correct the KERNEL_VERSION() macro in header file linux/kernel.h provided by kernel package to make things right. Thanks Best Jerry Song
