leandrof/linux
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

libbpf: Implement enum value-based CO-RE relocations

Browse Source 
Implement two relocations of a new enumerator value-based CO-RE relocation
kind: ENUMVAL_EXISTS and ENUMVAL_VALUE.

First, ENUMVAL_EXISTS, allows to detect the presence of a named enumerator
value in the target (kernel) BTF. This is useful to do BPF helper/map/program
type support detection from BPF program side. bpf_core_enum_value_exists()
macro helper is provided to simplify built-in usage.

Second, ENUMVAL_VALUE, allows to capture enumerator integer value and relocate
it according to the target BTF, if it changes. This is useful to have
a guarantee against intentional or accidental re-ordering/re-numbering of some
of the internal (non-UAPI) enumerations, where kernel developers don't care
about UAPI backwards compatiblity concerns. bpf_core_enum_value() allows to
capture this succinctly and use correct enum values in code.

LLVM uses ldimm64 instruction to capture enumerator value-based relocations,
so add support for ldimm64 instruction patching as well.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200819194519.3375898-5-andriin@fb.com
This commit is contained in:
Andrii Nakryiko
2020-08-19 12:45:18 -07:00
committed by Alexei Starovoitov
parent 4836bf5e2e
commit eacaaed784
3 changed files with 170 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
tools/lib/bpf/libbpf_internal.h
View File

@@ -242,6 +242,8 @@ enum bpf_core_relo_kind {
BPF_TYPE_ID_TARGET = 7, /* type ID in target kernel */
BPF_TYPE_EXISTS = 8, /* type existence in target kernel */
BPF_TYPE_SIZE = 9, /* type size in bytes */
BPF_ENUMVAL_EXISTS = 10, /* enum value existence in target kernel */
BPF_ENUMVAL_VALUE = 11, /* enum value integer value */
};
/* The minimum bpf_core_relo checked by the loader