linux-kernel - Re: [PATCH] libbpf: correct the macro KERNEL

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Date:   Mon, 17 Apr 2023 14:36:57 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     "songrui.771" <songrui.771@...edance.com>
Cc:     Andrii Nakryiko <andrii@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] libbpf: correct the macro KERNEL_VERSION for old kernel

On Mon, Apr 17, 2023 at 04:44:49PM +0800, songrui.771 wrote:
> 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@...edance.com>

This needs to be your name, not your email alias (do you use ".771" as a
name to sign things with?)

> ---
>  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?

thanks,

greg k-h