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From:   Nathan Chancellor <nathan@kernel.org>
To:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>
Cc:     Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
        Zi Shen Lim <zlim.lnx@gmail.com>,
        Xu Kuohai <xukuohai@huawei.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, bpf@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        llvm@lists.linux.dev, patches@lists.linux.dev,
        Nathan Chancellor <nathan@kernel.org>,
        Sami Tolvanen <samitolvanen@google.com>
Subject: [PATCH] bpf, arm64: Mark dummy_tramp as global
Date:   Wed, 13 Jul 2022 10:35:03 -0700
Message-Id: <20220713173503.3889486-1-nathan@kernel.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

When building with clang + CONFIG_CFI_CLANG=y, the following error
occurs at link time:

  ld.lld: error: undefined symbol: dummy_tramp

dummy_tramp is declared globally in C but its definition in inline
assembly does not use .global, which prevents clang from properly
resolving the references to it when creating the CFI jump tables.

Mark dummy_tramp as global so that the reference can be properly
resolved.

Fixes: b2ad54e1533e ("bpf, arm64: Implement bpf_arch_text_poke() for arm64")
Link: https://github.com/ClangBuiltLinux/linux/issues/1661
Suggested-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 arch/arm64/net/bpf_jit_comp.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index fd1cb0d2aaa6..dcc572b7d4da 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -604,6 +604,7 @@ void dummy_tramp(void);
 
 asm (
 "	.pushsection .text, \"ax\", @progbits\n"
+"	.global dummy_tramp\n"
 "	.type dummy_tramp, %function\n"
 "dummy_tramp:"
 #if IS_ENABLED(CONFIG_ARM64_BTI_KERNEL)

base-commit: ace2bee839e08df324cb320763258dfd72e6120e
-- 
2.37.1