linux-kernel - [PATCH AUTOSEL 5.4 34/80] selftests/bpf: Define string const as global for test_sysctl

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Date:   Mon, 26 Oct 2020 19:54:30 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Yonghong Song <yhs@...com>, Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andriin@...com>,
        Sasha Levin <sashal@...nel.org>,
        linux-kselftest@...r.kernel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: [PATCH AUTOSEL 5.4 34/80] selftests/bpf: Define string const as global for test_sysctl_prog.c

From: Yonghong Song <yhs@...com>

[ Upstream commit 6e057fc15a2da4ee03eb1fa6889cf687e690106e ]

When tweaking llvm optimizations, I found that selftest build failed
with the following error:
  libbpf: elf: skipping unrecognized data section(6) .rodata.str1.1
  libbpf: prog 'sysctl_tcp_mem': bad map relo against '.L__const.is_tcp_mem.tcp_mem_name'
          in section '.rodata.str1.1'
  Error: failed to open BPF object file: Relocation failed
  make: *** [/work/net-next/tools/testing/selftests/bpf/test_sysctl_prog.skel.h] Error 255
  make: *** Deleting file `/work/net-next/tools/testing/selftests/bpf/test_sysctl_prog.skel.h'

The local string constant "tcp_mem_name" is put into '.rodata.str1.1' section
which libbpf cannot handle. Using untweaked upstream llvm, "tcp_mem_name"
is completely inlined after loop unrolling.

Commit 7fb5eefd7639 ("selftests/bpf: Fix test_sysctl_loop{1, 2}
failure due to clang change") solved a similar problem by defining
the string const as a global. Let us do the same here
for test_sysctl_prog.c so it can weather future potential llvm changes.

Signed-off-by: Yonghong Song <yhs@...com>
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Acked-by: Andrii Nakryiko <andriin@...com>
Link: https://lore.kernel.org/bpf/20200910202718.956042-1-yhs@fb.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 tools/testing/selftests/bpf/progs/test_sysctl_prog.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/bpf/progs/test_sysctl_prog.c b/tools/testing/selftests/bpf/progs/test_sysctl_prog.c
index 5cbbff416998c..4396faf33394a 100644
--- a/tools/testing/selftests/bpf/progs/test_sysctl_prog.c
+++ b/tools/testing/selftests/bpf/progs/test_sysctl_prog.c
@@ -19,11 +19,11 @@
 #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
 #endif
 
+const char tcp_mem_name[] = "net/ipv4/tcp_mem";
 static __always_inline int is_tcp_mem(struct bpf_sysctl *ctx)
 {
-	char tcp_mem_name[] = "net/ipv4/tcp_mem";
 	unsigned char i;
-	char name[64];
+	char name[sizeof(tcp_mem_name)];
 	int ret;
 
 	memset(name, 0, sizeof(name));
-- 
2.25.1