bpf: Add 64bit enum value support #3014
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Currently, BTF only supports upto 32bit enum value with BTF_KIND_ENUM.
But in kernel, some enum indeed has 64bit values, e.g.,
in uapi bpf.h, we have
enum {
BPF_F_INDEX_MASK = 0xffffffffULL,
BPF_F_CURRENT_CPU = BPF_F_INDEX_MASK,
BPF_F_CTXLEN_MASK = (0xfffffULL << 32),
};
In this case, BTF_KIND_ENUM will encode the value of BPF_F_CTXLEN_MASK
as 0, which certainly is incorrect.
This patch added a new btf kind, BTF_KIND_ENUM64, which permits
64bit value to cover the above use case. The BTF_KIND_ENUM64 has
the following three fields followed by the common type:
struct bpf_enum64 {
__u32 nume_off;
__u32 val_lo32;
__u32 val_hi32;
};
Currently, btf type section has an alignment of 4 as all element types
are u32. Representing the value with __u64 will introduce a pad
for bpf_enum64 and may also introduce misalignment for the 64bit value.
Hence, two members of val_hi32 and val_lo32 are chosen to avoid these issues.
The kflag is also introduced for BTF_KIND_ENUM and BTF_KIND_ENUM64
to indicate whether the value is signed or unsigned. The kflag intends
to provide consistent output of BTF C fortmat with the original
source code. For example, the original BTF_KIND_ENUM bit value is 0xffffffff.
The format C has two choices, printing out 0xffffffff or -1 and current libbpf
prints out as unsigned value. But if the signedness is preserved in btf,
the value can be printed the same as the original source code.
The kflag value 0 means unsigned values, which is consistent to the default
by libbpf and should also cover most cases as well.
The new BTF_KIND_ENUM64 is intended to support the enum value represented as
64bit value. But it can represent all BTF_KIND_ENUM values as well.
The compiler ([1]) and pahole will generate BTF_KIND_ENUM64 only if the value has
to be represented with 64 bits.
In addition, a static inline function btf_kind_core_compat() is introduced which
will be used later when libbpf relo_core.c changed. Here the kernel shares the
same relo_core.c with libbpf.
[1] https://reviews.llvm.org/D124641
Signed-off-by: Yonghong Song <yhs@fb.com>
Currently, the libbpf limits the relocation value to be 32bit since all current relocations have such a limit. But with BTF_KIND_ENUM64 support, the enum value could be 64bit. So let us permit 64bit relocation value in libbpf. Signed-off-by: Yonghong Song <yhs@fb.com>
Currently, the 64bit relocation value in the instruction is computed as follows: __u64 imm = insn[0].imm + ((__u64)insn[1].imm << 32) Suppose insn[0].imm = -1 (0xffffffff) and insn[1].imm = 1. With the above computation, insn[0].imm will first sign-extend to 64bit -1 (0xffffffffFFFFFFFF) and then add 0x1FFFFFFFF, producing incorrect value 0xFFFFFFFF. The correct value should be 0x1FFFFFFFF. Changing insn[0].imm to __u32 first will prevent 64bit sign extension and fix the issue. Merging high and low 32bit values also changed from '+' to '|' to be consistent with other similar occurences in kernel and libbpf. Acked-by: Dave Marchevsky <davemarchevsky@fb.com> Signed-off-by: Yonghong Song <yhs@fb.com>
Refactor btf__add_enum() function to create a separate function btf_add_enum_common() so later the common function can be used to add enum64 btf type. There is no functionality change for this patch. Signed-off-by: Yonghong Song <yhs@fb.com>
Add enum64 parsing support and two new enum64 public APIs: btf__add_enum64 btf__add_enum64_value Also add support of signedness for BTF_KIND_ENUM. The BTF_KIND_ENUM API signatures are not changed. The signedness will be changed from unsigned to signed if btf__add_enum_value() finds any negative values. Signed-off-by: Yonghong Song <yhs@fb.com>
Add enum64 deduplication support. BTF_KIND_ENUM64 handling is very similar to BTF_KIND_ENUM. Signed-off-by: Yonghong Song <yhs@fb.com>
Add enum64 btf dumping support. For long long and unsigned long long dump, suffixes 'LL' and 'ULL' are added to avoid compilation errors in some cases. Signed-off-by: Yonghong Song <yhs@fb.com>
When old kernel does not support enum64 but user space btf contains non-zero enum kflag or enum64, libbpf needs to do proper sanitization so modified btf can be accepted by the kernel. Sanitization for enum kflag can be achieved by clearing the kflag bit. For enum64, the type is replaced with an union of integer member types and the integer member size must be smaller than enum64 size. If such an integer type cannot be found, a new type is created and used for union members. Signed-off-by: Yonghong Song <yhs@fb.com>
Add BTF_KIND_ENUM64 support for bpf linking, which is very similar to BTF_KIND_ENUM. Signed-off-by: Yonghong Song <yhs@fb.com>
The enum64 relocation support is added. The bpf local type could be either enum or enum64 and the remote type could be either enum or enum64 too. The all combinations of local enum/enum64 and remote enum/enum64 are supported. Signed-off-by: Yonghong Song <yhs@fb.com>
Add BTF_KIND_ENUM64 support.
For example, the following enum is defined in uapi bpf.h.
$ cat core.c
enum A {
BPF_F_INDEX_MASK = 0xffffffffULL,
BPF_F_CURRENT_CPU = BPF_F_INDEX_MASK,
BPF_F_CTXLEN_MASK = (0xfffffULL << 32),
} g;
Compiled with
clang -target bpf -O2 -g -c core.c
Using bpftool to dump types and generate format C file:
$ bpftool btf dump file core.o
...
[1] ENUM64 'A' size=8 vlen=3
'BPF_F_INDEX_MASK' val=4294967295ULL
'BPF_F_CURRENT_CPU' val=4294967295ULL
'BPF_F_CTXLEN_MASK' val=4503595332403200ULL
$ bpftool btf dump file core.o format c
...
enum A {
BPF_F_INDEX_MASK = 4294967295ULL,
BPF_F_CURRENT_CPU = 4294967295ULL,
BPF_F_CTXLEN_MASK = 4503595332403200ULL,
};
...
The 64bit value is represented properly in BTF and C dump.
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Yonghong Song <yhs@fb.com>
The kflag is supported now for BTF_KIND_ENUM. So remove the test which tests verifier failure due to existence of kflag. Signed-off-by: Yonghong Song <yhs@fb.com>
Add tests to use the new enum kflag and enum64 API functions in selftest btf_write. Signed-off-by: Yonghong Song <yhs@fb.com>
Add unit tests for basic BTF_KIND_ENUM64 encoding. Signed-off-by: Yonghong Song <yhs@fb.com>
Add a few unit tests for BTF_KIND_ENUM64 deduplication. Signed-off-by: Yonghong Song <yhs@fb.com>
Add a test for enum64 value relocations. Signed-off-by: Yonghong Song <yhs@fb.com>
Certain subtests in selftests core_reloc and core_reloc_btfgen requires llvm ENUM64 support in llvm15. If an older compiler is used, these subtests will fail. Make this requirement clear in selftests README.rst file. Signed-off-by: Yonghong Song <yhs@fb.com>
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Master branch: 68084a1 |
Add BTF_KIND_ENUM64 documentation in btf.rst. Also fixed a typo for section number for BTF_KIND_TYPE_TAG from 2.2.17 to 2.2.18. Signed-off-by: Yonghong Song <yhs@fb.com>
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At least one diff in series https://patchwork.kernel.org/project/netdevbpf/list/?series=641621 expired. Closing PR. |
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Pull request for series with
subject: bpf: Add 64bit enum value support
version: 2
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=641621