Commit 54b8625c authored Oct 18, 2019 by John Fastabend Committed by Daniel Borkmann Oct 18, 2019

bpf, libbpf: Add kernel version section parsing back

With commit "libbpf: stop enforcing kern_version,..." we removed the
kernel version section parsing in favor of querying for the kernel
using uname() and populating the version using the result of the
query. After this any version sections were simply ignored.

Unfortunately, the world of kernels is not so friendly. I've found some
customized kernels where uname() does not match the in kernel version.
To fix this so programs can load in this environment this patch adds
back parsing the section and if it exists uses the user specified
kernel version to override the uname() result. However, keep most the
kernel uname() discovery bits so users are not required to insert the
version except in these odd cases.

Fixes: 5e61f270 ("libbpf: stop enforcing kern_version, populate it for users")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/157140968634.9073.6407090804163937103.stgit@john-XPS-13-9370

parent 1f5343c0

tools/lib/bpf/libbpf.c

+20 −1

Original line number	Diff line number	Diff line
		@@ -657,6 +657,21 @@ bpf_object__init_license(struct bpf_object obj, void data, size_t size)
		return 0;
		}

		static int
		bpf_object__init_kversion(struct bpf_object obj, void data, size_t size)
		{
		__u32 kver;

		if (size != sizeof(kver)) {
		pr_warning("invalid kver section in %s\n", obj->path);
		return -LIBBPF_ERRNO__FORMAT;
		}
		memcpy(&kver, data, sizeof(kver));
		obj->kern_version = kver;
		pr_debug("kernel version of %s is %x\n", obj->path, obj->kern_version);
		return 0;
		}

		static int compare_bpf_map(const void _a, const void _b)
		{
		const struct bpf_map *a = _a;
		@@ -1574,7 +1589,11 @@ static int bpf_object__elf_collect(struct bpf_object *obj, bool relaxed_maps)
		if (err)
		return err;
		} else if (strcmp(name, "version") == 0) {
		/* skip, we don't need it anymore */
		err = bpf_object__init_kversion(obj,
		data->d_buf,
		data->d_size);
		if (err)
		return err;
		} else if (strcmp(name, "maps") == 0) {
		obj->efile.maps_shndx = idx;
		} else if (strcmp(name, MAPS_ELF_SEC) == 0) {

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