From: Andrii Nakryiko <andriin@fb.com>
To: <bpf@vger.kernel.org>, <netdev@vger.kernel.org>, <ast@fb.com>,
<daniel@iogearbox.net>
Cc: <andrii.nakryiko@gmail.com>, <kernel-team@fb.com>,
Andrii Nakryiko <andriin@fb.com>
Subject: [PATCH v2 bpf-next 4/6] bpftool: apply preserve_access_index attribute to all types in BTF dump
Date: Sun, 12 Jan 2020 23:31:41 -0800 [thread overview]
Message-ID: <20200113073143.1779940-5-andriin@fb.com> (raw)
In-Reply-To: <20200113073143.1779940-1-andriin@fb.com>
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>
---
tools/bpf/bpftool/btf.c | 8 ++++++++
1 file changed, 8 insertions(+)
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;
--
2.17.1
next prev parent reply other threads:[~2020-01-13 7:32 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-13 7:31 [PATCH v2 bpf-next 0/6] Implement runqslower BCC tool with BPF CO-RE Andrii Nakryiko
2020-01-13 7:31 ` [PATCH v2 bpf-next 1/6] tools: sync uapi/linux/if_link.h Andrii Nakryiko
2020-01-13 7:31 ` [PATCH v2 bpf-next 2/6] libbpf: clean up bpf_helper_defs.h generation output Andrii Nakryiko
2020-01-13 7:31 ` [PATCH v2 bpf-next 3/6] selftests/bpf: conform selftests/bpf Makefile output to libbpf and bpftool Andrii Nakryiko
2020-01-13 7:31 ` Andrii Nakryiko [this message]
2020-01-13 7:31 ` [PATCH v2 bpf-next 5/6] tools/bpf: add runqslower tool to tools/bpf Andrii Nakryiko
2020-01-14 13:22 ` Jiri Olsa
2020-01-14 17:25 ` Alexei Starovoitov
2020-01-14 18:42 ` Jiri Olsa
2020-01-13 7:31 ` [PATCH v2 bpf-next 6/6] selftests/bpf: build runqslower from selftests Andrii Nakryiko
2020-01-14 2:15 ` [PATCH v2 bpf-next 0/6] Implement runqslower BCC tool with BPF CO-RE Alexei Starovoitov
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