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author | Andrii Nakryiko <andriin@fb.com> | 2020-01-12 23:31:41 -0800 |
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committer | Alexei Starovoitov <ast@kernel.org> | 2020-01-13 17:48:13 -0800 |
commit | 1cf5b23988ea0086a252a5c8b005b075f1e9b030 (patch) | |
tree | 8dabe0a326970a8b8a47ce8457b9530dad94f744 /tools/bpf/bpftool | |
parent | 2cc51d34d93c9cf76128da6535a2a0a38c9faddb (diff) | |
download | linux-1cf5b23988ea0086a252a5c8b005b075f1e9b030.tar.bz2 |
bpftool: Apply preserve_access_index attribute to all types in BTF dump
This patch makes structs and unions, emitted through BTF dump, automatically
CO-RE-relocatable (unless disabled with `#define BPF_NO_PRESERVE_ACCESS_INDEX`,
specified before including generated header file).
This effectivaly turns usual bpf_probe_read() call into equivalent of
bpf_core_read(), by automatically applying builtin_preserve_access_index to
any field accesses of types in generated C types header.
This is especially useful for tp_btf/fentry/fexit BPF program types. They
allow direct memory access, so BPF C code just uses straightfoward a->b->c
access pattern to read data from kernel. But without kernel structs marked as
CO-RE relocatable through preserve_access_index attribute, one has to enclose
all the data reads into a special __builtin_preserve_access_index code block,
like so:
__builtin_preserve_access_index(({
x = p->pid; /* where p is struct task_struct *, for example */
}));
This is very inconvenient and obscures the logic quite a bit. By marking all
auto-generated types with preserve_access_index attribute the above code is
reduced to just a clean and natural `x = p->pid;`.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200113073143.1779940-5-andriin@fb.com
Diffstat (limited to 'tools/bpf/bpftool')
-rw-r--r-- | tools/bpf/bpftool/btf.c | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c index e5bc97b71ceb..60c75be0666d 100644 --- a/tools/bpf/bpftool/btf.c +++ b/tools/bpf/bpftool/btf.c @@ -370,6 +370,10 @@ static int dump_btf_c(const struct btf *btf, if (IS_ERR(d)) return PTR_ERR(d); + printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n"); + printf("#pragma clang attribute push (__attribute__((preserve_access_index)), apply_to = record)\n"); + printf("#endif\n\n"); + if (root_type_cnt) { for (i = 0; i < root_type_cnt; i++) { err = btf_dump__dump_type(d, root_type_ids[i]); @@ -386,6 +390,10 @@ static int dump_btf_c(const struct btf *btf, } } + printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n"); + printf("#pragma clang attribute pop\n"); + printf("#endif\n"); + done: btf_dump__free(d); return err; |