From: Andrii Nakryiko <andrii@kernel.org>
To: <bpf@vger.kernel.org>, <netdev@vger.kernel.org>, <ast@fb.com>,
<daniel@iogearbox.net>
Cc: <andrii@kernel.org>, <kernel-team@fb.com>
Subject: [RFC PATCH bpf-next 4/7] bpftool: stop emitting static variables in BPF skeleton
Date: Thu, 6 May 2021 22:41:16 -0700 [thread overview]
Message-ID: <20210507054119.270888-5-andrii@kernel.org> (raw)
In-Reply-To: <20210507054119.270888-1-andrii@kernel.org>
As discussed in [0], stop emitting static variables in BPF skeletons to avoid
issues with name-conflicting static variables across multiple
statically-linked BPF object files.
Users using static variables to pass data between BPF programs and user-space
should do a trivial one-time switch according to the following simple rules:
- read-only `static volatile const` variables should be converted to
`volatile const`;
- read/write `static volatile` variables should just drop `static volatile`
modifiers to become global variables/symbols. To better handle older Clang
versions, such newly converted global variables should be explicitly
initialized with a specific value or `= 0`/`= {}`, whichever is
appropriate.
[0] https://lore.kernel.org/bpf/CAEf4BzZo7_r-hsNvJt3w3kyrmmBJj7ghGY8+k4nvKF0KLjma=w@mail.gmail.com/T/#m664d4b0d6b31ac8b2669360e0fc2d6962e9f5ec1
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
tools/bpf/bpftool/gen.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 06fee4a2910a..27dceaf66ecb 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -131,6 +131,10 @@ static int codegen_datasec_def(struct bpf_object *obj,
int need_off = sec_var->offset, align_off, align;
__u32 var_type_id = var->type;
+ /* static variables are not exposed through BPF skeleton */
+ if (btf_var(var)->linkage == BTF_VAR_STATIC)
+ continue;
+
if (off > need_off) {
p_err("Something is wrong for %s's variable #%d: need offset %d, already at %d.\n",
sec_name, i, need_off, off);
--
2.30.2
next prev parent reply other threads:[~2021-05-07 5:41 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-07 5:41 [RFC PATCH bpf-next 0/7] BPF static linker: global symbols visibility Andrii Nakryiko
2021-05-07 5:41 ` [RFC PATCH bpf-next 1/7] bpftool: strip const/volatile/restrict modifiers from .bss and .data vars Andrii Nakryiko
2021-05-07 5:41 ` [RFC PATCH bpf-next 2/7] libbpf: add per-file linker opts Andrii Nakryiko
2021-05-07 5:41 ` [RFC PATCH bpf-next 3/7] selftests/bpf: stop using static variables for passing data to/from user-space Andrii Nakryiko
2021-05-07 5:41 ` Andrii Nakryiko [this message]
2021-05-07 5:41 ` [RFC PATCH bpf-next 5/7] libbpf: fix ELF symbol visibility update logic Andrii Nakryiko
2021-05-07 5:41 ` [RFC PATCH bpf-next 6/7] libbpf: treat STV_INTERNAL same as STV_HIDDEN for functions Andrii Nakryiko
2021-05-07 5:41 ` [RFC PATCH bpf-next 7/7] libbpf: convert STV_HIDDEN symbols into STV_INTERNAL after linking Andrii Nakryiko
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