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libbpf: Support kernel module function calls

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This patch adds libbpf support for kernel module function call support.
The fd_array parameter is used during BPF program load to pass module
BTFs referenced by the program. insn->off is set to index into this
array, but starts from 1, because insn->off as 0 is reserved for
btf_vmlinux.

We try to use existing insn->off for a module, since the kernel limits
the maximum distinct module BTFs for kfuncs to 256, and also because
index must never exceed the maximum allowed value that can fit in
insn->off (INT16_MAX). In the future, if kernel interprets signed offset
as unsigned for kfunc calls, this limit can be increased to UINT16_MAX.

Also introduce a btf__find_by_name_kind_own helper to start searching
from module BTF's start id when we know that the BTF ID is not present
in vmlinux BTF (in find_ksym_btf_id).

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211002011757.311265-7-memxor@gmail.com
This commit is contained in:
Kumar Kartikeya Dwivedi
2021-10-02 06:47:54 +05:30
committed by Andrii Nakryiko
parent 962f241379
commit 7dde8f8f8d
4 changed files with 72 additions and 24 deletions
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18
src/btf.c
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@@ -695,15 +695,15 @@ __s32 btf__find_by_name(const struct btf *btf, const char *type_name)
return libbpf_err(-ENOENT);
}
__s32 btf__find_by_name_kind(const struct btf *btf, const char *type_name,
__u32 kind)
static __s32 btf_find_by_name_kind(const struct btf *btf, int start_id,
const char *type_name, __u32 kind)
{
__u32 i, nr_types = btf__get_nr_types(btf);
if (kind == BTF_KIND_UNKN || !strcmp(type_name, "void"))
return 0;
for (i = 1; i <= nr_types; i++) {
for (i = start_id; i <= nr_types; i++) {
const struct btf_type *t = btf__type_by_id(btf, i);
const char *name;
@@ -717,6 +717,18 @@ __s32 btf__find_by_name_kind(const struct btf *btf, const char *type_name,
return libbpf_err(-ENOENT);
}
__s32 btf__find_by_name_kind_own(const struct btf *btf, const char *type_name,
__u32 kind)
{
return btf_find_by_name_kind(btf, btf->start_id, type_name, kind);
}
__s32 btf__find_by_name_kind(const struct btf *btf, const char *type_name,
__u32 kind)
{
return btf_find_by_name_kind(btf, 1, type_name, kind);
}
static bool btf_is_modifiable(const struct btf *btf)
{
return (void *)btf->hdr != btf->raw_data;