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author | John Fastabend <john.fastabend@gmail.com> | 2018-04-23 12:11:02 -0700 |
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committer | Daniel Borkmann <daniel@iogearbox.net> | 2018-04-23 23:42:21 +0200 |
commit | 514d6c1959f9b396f1b51850925900adedffb951 (patch) | |
tree | f806288e530b2d6623b599123bea3d229a37d68d /Documentation | |
parent | 6899b32b5b2dee358936b82b8363b716607a138f (diff) | |
download | linux-514d6c1959f9b396f1b51850925900adedffb951.tar.bz2 |
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>
Diffstat (limited to 'Documentation')
-rw-r--r-- | Documentation/bpf/bpf_devel_QA.txt | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/Documentation/bpf/bpf_devel_QA.txt b/Documentation/bpf/bpf_devel_QA.txt index 1a0b704e1a38..da57601153a0 100644 --- a/Documentation/bpf/bpf_devel_QA.txt +++ b/Documentation/bpf/bpf_devel_QA.txt @@ -557,6 +557,14 @@ A: Although LLVM IR generation and optimization try to stay architecture pulls in some header files containing file scope host assembly codes. - You can add "-fno-jump-tables" to work around the switch table issue. - Otherwise, you can use bpf target. + Otherwise, you can use bpf target. Additionally, you _must_ use bpf target + when: + + - Your program uses data structures with pointer or long / unsigned long + types that interface with BPF helpers or context data structures. Access + into these structures is verified by the BPF verifier and may result + in verification failures if the native architecture is not aligned with + the BPF architecture, e.g. 64-bit. An example of this is + BPF_PROG_TYPE_SK_MSG require '-target bpf' Happy BPF hacking! |