bpf: Document sockmap '-target bpf' requirement for PROG_TYPE_SK_MSG
BPF_PROG_TYPE_SK_MSG programs use a 'void *' for both data and the data_end pointers. Additionally, the verifier ensures that every accesses into the values is a __u64 read. This correctly maps on to the BPF 64-bit architecture. However, to ensure that when building on 32bit architectures that clang uses correct types the '-target bpf' option _must_ be specified. To make this clear add a note to the Documentation. Signed-off-by: John Fastabend <john.fastabend@gmail.com> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
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@ -557,6 +557,14 @@ A: Although LLVM IR generation and optimization try to stay architecture
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pulls in some header files containing file scope host assembly codes.
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pulls in some header files containing file scope host assembly codes.
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- You can add "-fno-jump-tables" to work around the switch table issue.
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- You can add "-fno-jump-tables" to work around the switch table issue.
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Otherwise, you can use bpf target.
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Otherwise, you can use bpf target. Additionally, you _must_ use bpf target
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when:
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- Your program uses data structures with pointer or long / unsigned long
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types that interface with BPF helpers or context data structures. Access
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into these structures is verified by the BPF verifier and may result
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in verification failures if the native architecture is not aligned with
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the BPF architecture, e.g. 64-bit. An example of this is
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BPF_PROG_TYPE_SK_MSG require '-target bpf'
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Happy BPF hacking!
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Happy BPF hacking!
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