On Thu, Nov 19, 2020 at 03:22:42PM -0800, Andrii Nakryiko wrote:
> Teach libbpf to search for candidate types for CO-RE relocations across kernel
> modules BTFs, in addition to vmlinux BTF. If at least one candidate type is
> found in vmlinux BTF, kernel module BTFs are not iterated. If vmlinux BTF has
> no matching candidates, then find all kernel module BTFs and search for all
> matching candidates across all of them.
>
> Kernel's support for module BTFs are inferred from the support for BTF name
> pointer in BPF UAPI.
>
> Signed-off-by: Andrii Nakryiko <and...@kernel.org>
> ---
> tools/lib/bpf/libbpf.c | 185 ++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 172 insertions(+), 13 deletions(-)
>
[...]
> +static int probe_module_btf(void)
> +{
> + static const char strs[] = "\0int";
> + __u32 types[] = {
> + /* int */
> + BTF_TYPE_INT_ENC(1, BTF_INT_SIGNED, 0, 32, 4),
> + };
> + struct bpf_btf_info info;
> + __u32 len = sizeof(info);
> + char name[16];
> + int fd, err;
> +
> + fd = libbpf__load_raw_btf((char *)types, sizeof(types), strs,
> sizeof(strs));
> + if (fd < 0)
> + return 0; /* BTF not supported at all */
> +
> + len = sizeof(info);
nit: reinit of len
> + memset(&info, 0, sizeof(info));
use len in memset
> + info.name = ptr_to_u64(name);
> + info.name_len = sizeof(name);
> +
> + /* check that BPF_OBJ_GET_INFO_BY_FD supports specifying name pointer;
> + * kernel's module BTF support coincides with support for
> + * name/name_len fields in struct bpf_btf_info.
> + */
> + err = bpf_obj_get_info_by_fd(fd, &info, &len);
> + close(fd);
> + return !err;
> +}
[...]
