On 8/18/20 10:28 PM, Andrii Nakryiko wrote:
This patch set adds libbpf support for two new classes of CO-RE relocations:
type-based (TYPE_EXISTS/TYPE_SIZE/TYPE_ID_LOCAL/TYPE_ID_TARGET) and enum
value-vased (ENUMVAL_EXISTS/ENUMVAL_VALUE):
- TYPE_EXISTS allows to detect presence in kernel BTF of a locally-recorded
BTF type. Useful for feature detection (new functionality often comes with
new internal kernel types), as well as handling type renames and bigger
refactorings.
- TYPE_SIZE allows to get the real size (in bytes) of a specified kernel
type. Useful for dumping internal structure as-is through perfbuf or
ringbuf.
- TYPE_ID_LOCAL/TYPE_ID_TARGET allow to capture BTF type ID of a BTF type in
program's BTF or kernel BTF, respectively. These could be used for
high-performance and space-efficient generic data dumping/logging by
relying on small and cheap BTF type ID as a data layout descriptor, for
post-processing on user-space side.
- ENUMVAL_EXISTS can be used for detecting the presence of enumerator value
in kernel's enum type. Most direct application is to detect BPF helper
support in kernel.
- ENUMVAL_VALUE allows to relocate real integer value of kernel enumerator
value, which is subject to change (e.g., always a potential issue for
internal, non-UAPI, kernel enums).
I've indicated potential applications for these relocations, but relocations
themselves are generic and unassuming and are designed to work correctly even
in unintended applications. Furthermore, relocated values become constants,
known to the verifier and could and would be used for dead branch code
detection and elimination. This makes them ideal to do all sorts of feature
detection and guarding functionality that's not available on some older (but
still supported by BPF program) kernels, while having to compile and maintain
one unified source code.
Selftests are added for all the new features. Selftests utilizing new Clang
built-ins are designed such that they will compile with older Clangs and will
be skipped during test runs. So this shouldn't cause any build and test
failures on systems with slightly outdated Clang compiler.
LLVM patches adding these relocation in Clang:
- __builtin_btf_type_id() ([0], [1], [2]);
- __builtin_preserve_type_info(), __builtin_preserve_enum_value() ([3], [4]).
[0] https://urldefense.proofpoint.com/v2/url?u=https-3A__reviews.llvm.org_D74572&d=DwIFAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=Sr14A5U1sClCcGVCk0rEi3mKHUVfuqMPeiM1_clUDhA&s=aOQT0NmQAfxLsMwCsIJjEkiZHZEe_Gu3KbH_KzcvJwg&e=
[1] https://urldefense.proofpoint.com/v2/url?u=https-3A__reviews.llvm.org_D74668&d=DwIFAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=Sr14A5U1sClCcGVCk0rEi3mKHUVfuqMPeiM1_clUDhA&s=0Dal6DRCFzut_D-NAd72XZSra5qiBLDZD8E2YVQbIsQ&e=
[2] https://urldefense.proofpoint.com/v2/url?u=https-3A__reviews.llvm.org_D85174&d=DwIFAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=Sr14A5U1sClCcGVCk0rEi3mKHUVfuqMPeiM1_clUDhA&s=1gWWaCVLCsmvdZalFuQNxINYvv1We4yRQ2VRyreJe3A&e=
[3] https://urldefense.proofpoint.com/v2/url?u=https-3A__reviews.llvm.org_D83878&d=DwIFAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=Sr14A5U1sClCcGVCk0rEi3mKHUVfuqMPeiM1_clUDhA&s=HvZx6wUsq8kazfavPBRGWFH6zEDYjfkrpvvsC2UgWjI&e=
[4] https://urldefense.proofpoint.com/v2/url?u=https-3A__reviews.llvm.org_D83242&d=DwIFAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=Sr14A5U1sClCcGVCk0rEi3mKHUVfuqMPeiM1_clUDhA&s=Y_Dg-Tl0lQOtbD36XQjZ20P2T7exTymmzqklOqC-USI&e=
v1->v2:
- selftests detect built-in support and are skipped if not found (Alexei).
Andrii Nakryiko (5):
libbpf: implement type-based CO-RE relocations support
selftests/bpf: test TYPE_EXISTS and TYPE_SIZE CO-RE relocations
selftests/bpf: add CO-RE relo test for TYPE_ID_LOCAL/TYPE_ID_TARGET
libbpf: implement enum value-based CO-RE relocations
selftests/bpf: add tests for ENUMVAL_EXISTS/ENUMVAL_VALUE relocations
tools/lib/bpf/bpf_core_read.h | 80 +++-
tools/lib/bpf/libbpf.c | 376 ++++++++++++++++--
tools/lib/bpf/libbpf_internal.h | 6 +
.../selftests/bpf/prog_tests/core_reloc.c | 349 ++++++++++++++--
.../bpf/progs/btf__core_reloc_enumval.c | 3 +
.../progs/btf__core_reloc_enumval___diff.c | 3 +
.../btf__core_reloc_enumval___err_missing.c | 3 +
.../btf__core_reloc_enumval___val3_missing.c | 3 +
.../bpf/progs/btf__core_reloc_type_based.c | 3 +
...btf__core_reloc_type_based___all_missing.c | 3 +
.../btf__core_reloc_type_based___diff_sz.c | 3 +
...f__core_reloc_type_based___fn_wrong_args.c | 3 +
.../btf__core_reloc_type_based___incompat.c | 3 +
.../bpf/progs/btf__core_reloc_type_id.c | 3 +
...tf__core_reloc_type_id___missing_targets.c | 3 +
.../selftests/bpf/progs/core_reloc_types.h | 327 ++++++++++++++-
.../bpf/progs/test_core_reloc_enumval.c | 73 ++++
.../bpf/progs/test_core_reloc_kernel.c | 2 +
.../bpf/progs/test_core_reloc_type_based.c | 111 ++++++
.../bpf/progs/test_core_reloc_type_id.c | 107 +++++
20 files changed, 1408 insertions(+), 56 deletions(-)
create mode 100644 tools/testing/selftests/bpf/progs/btf__core_reloc_enumval.c
create mode 100644 tools/testing/selftests/bpf/progs/btf__core_reloc_enumval___diff.c
create mode 100644 tools/testing/selftests/bpf/progs/btf__core_reloc_enumval___err_missing.c
create mode 100644 tools/testing/selftests/bpf/progs/btf__core_reloc_enumval___val3_missing.c
create mode 100644 tools/testing/selftests/bpf/progs/btf__core_reloc_type_based.c
create mode 100644 tools/testing/selftests/bpf/progs/btf__core_reloc_type_based___all_missing.c
create mode 100644 tools/testing/selftests/bpf/progs/btf__core_reloc_type_based___diff_sz.c
create mode 100644 tools/testing/selftests/bpf/progs/btf__core_reloc_type_based___fn_wrong_args.c
create mode 100644 tools/testing/selftests/bpf/progs/btf__core_reloc_type_based___incompat.c
create mode 100644 tools/testing/selftests/bpf/progs/btf__core_reloc_type_id.c
create mode 100644 tools/testing/selftests/bpf/progs/btf__core_reloc_type_id___missing_targets.c
create mode 100644 tools/testing/selftests/bpf/progs/test_core_reloc_enumval.c
create mode 100644 tools/testing/selftests/bpf/progs/test_core_reloc_type_based.c
create mode 100644 tools/testing/selftests/bpf/progs/test_core_reloc_type_id.c
Thanks for implementing this new btf relocations in libbpf.
Hopefully people will find them useful and start to use them once clang
12 becomes widely available.
I do have a few nits when I apply the patch to my local bpf-next and
one suggestion for change. With that,
Acked-by: Yonghong Song <yhs@xxxxxx>
