bpf: Add 64bit enum value support #2953
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Master branch: 20b87e7 |
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 bytes followed by the common type:
struct bpf_enum64 {
__u32 nume_off;
__u32 hi32;
__u32 lo32;
};
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 hi32 and 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, print 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 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 value size of BTF_KIND_ENUM64 is encoded to 8 to represent its intent.
The compiler ([1]) and pahole will generate BTF_KIND_ENUM64 only if the value has
to be represented with 64 bits.
[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. Signed-off-by: Yonghong Song <yhs@fb.com> Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com> Acked-by: Dave Marchevsky <davemarchevsky@fb.com>
Add BTF_KIND_ENUM64 support. Deprecated btf__add_enum() and btf__add_enum_value() and introduced the following new APIs btf__add_enum32() btf__add_enum32_value() btf__add_enum64() btf__add_enum64_value() due to new kind and introduction of kflag. To support old kernel with enum64, the sanitization is added to replace BTF_KIND_ENUM64 with a bunch of pointer-to-void types. The enum64 value relocation is also supported. The enum64 forward resolution, with enum type as forward declaration and enum64 as the actual definition, is also supported. Signed-off-by: Yonghong Song <yhs@fb.com> Reported-by: kernel test robot <lkp@intel.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.
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.
With enum64 support in kernel and libbpf,
selftest btf_dump/btf_dump failed with
no-enum64 support llvm for the following
enum definition:
enum e2 {
C = 100,
D = 4294967295,
E = 0,
};
With the no-enum64 support llvm, the signedness is
'signed' by default, and D (4294967295 = 0xffffffff)
will print as -1. With enum64 support llvm, the signedness
is 'unsigned' and the value of D will print as 4294967295.
To support both old and new compilers, this patch
changed the value to 268435455 = 0xfffffff which works
with both enum64 or non-enum64 support llvm.
Signed-off-by: Yonghong Song <yhs@fb.com>
Acked-by: Dave Marchevsky <davemarchevsky@fb.com>
Add tests to use the newer libbpf enum32/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>
Signed-off-by: Yonghong Song <yhs@fb.com>
Add a test for enum64 value relocations. Signed-off-by: Yonghong Song <yhs@fb.com>
|
Master branch: 7b3a063 |
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>
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=637423 expired. Closing PR. |
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Pull request for series with
subject: bpf: Add 64bit enum value support
version: 1
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=637423