linux-kernel - [PATCH v2] bpf: Fix BTF_ID symbol generation collision

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Date:   Fri, 15 Sep 2023 09:42:20 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, stable@...r.kernel.org,
        Satya Durga Srinivasu Prabhala <quic_satyap@...cinc.com>,
        Marcus Seyfarth <m.seyfarth@...il.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: [PATCH v2] bpf: Fix BTF_ID symbol generation collision

Marcus and Satya reported an issue where BTF_ID macro generates same
symbol in separate objects and that breaks final vmlinux link.

  ld.lld: error: ld-temp.o <inline asm>:14577:1: symbol
  '__BTF_ID__struct__cgroup__624' is already defined

This can be triggered under specific configs when __COUNTER__ happens to
be the same for the same symbol in two different translation units,
which is already quite unlikely to happen.

Add __LINE__ number suffix to make BTF_ID symbol more unique, which is
not a complete fix, but it would help for now and meanwhile we can work
on better solution as suggested by Andrii.

Cc: stable@...r.kernel.org
Reported-by: Satya Durga Srinivasu Prabhala <quic_satyap@...cinc.com>
Reported-by: Marcus Seyfarth <m.seyfarth@...il.com>
Closes: https://github.com/ClangBuiltLinux/linux/issues/1913
Tested-by: Marcus Seyfarth <m.seyfarth@...il.com>
Debugged-by: Nathan Chancellor <nathan@...nel.org>
Co-developed-by: Jiri Olsa <jolsa@...nel.org>
Link: https://lore.kernel.org/bpf/CAEf4Bzb5KQ2_LmhN769ifMeSJaWfebccUasQOfQKaOd0nQ51tw@mail.gmail.com/
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
 tools/include/linux/btf_ids.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/include/linux/btf_ids.h b/tools/include/linux/btf_ids.h
index 71e54b1e3796..30e920b96a18 100644
--- a/tools/include/linux/btf_ids.h
+++ b/tools/include/linux/btf_ids.h
@@ -38,7 +38,7 @@ asm(							\
 	____BTF_ID(symbol)
 
 #define __ID(prefix) \
-	__PASTE(prefix, __COUNTER__)
+	__PASTE(prefix, __COUNTER__ __LINE__)
 
 /*
  * The BTF_ID defines unique symbol for each ID pointing

---
base-commit: 9fdfb15a3dbf818e06be514f4abbfc071004cbe7
change-id: 20230915-bpf_collision-36889a391d44

Best regards,
-- 
Nick Desaulniers <ndesaulniers@...gle.com>