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authorAndrii Nakryiko2020-01-12 23:31:41 -0800
committerAlexei Starovoitov2020-01-13 17:48:13 -0800
commit1cf5b23988ea0086a252a5c8b005b075f1e9b030 (patch)
tree8dabe0a326970a8b8a47ce8457b9530dad94f744
parent2cc51d34d93c9cf76128da6535a2a0a38c9faddb (diff)
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
-rw-r--r--tools/bpf/bpftool/btf.c8
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;