linux-kernel - [PATCH] perf build: Suppress openssl v3 deprecation warnings in libcrypto feature test

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Date:   Sat, 25 Jun 2022 23:34:38 +0800
From:   Zixuan Tan <tanzixuangg@...il.com>
To:     terrelln@...com
Cc:     Zixuan Tan <tanzixuan.me@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: [PATCH] perf build: Suppress openssl v3 deprecation warnings in libcrypto feature test

With OpenSSL v3 installed, the libcrypto feature check fails as it use the
deprecated MD5_* API (and is compiled with -Werror). The error message is
as follows.

$ make tools/perf
```
Makefile.config:778: No libcrypto.h found, disables jitted code injection,
please install openssl-devel or libssl-dev

Auto-detecting system features:
...                         dwarf: [ on  ]
...            dwarf_getlocations: [ on  ]
...                         glibc: [ on  ]
...                        libbfd: [ on  ]
...                libbfd-buildid: [ on  ]
...                        libcap: [ on  ]
...                        libelf: [ on  ]
...                       libnuma: [ on  ]
...        numa_num_possible_cpus: [ on  ]
...                       libperl: [ on  ]
...                     libpython: [ on  ]
...                     libcrypto: [ OFF ]
...                     libunwind: [ on  ]
...            libdw-dwarf-unwind: [ on  ]
...                          zlib: [ on  ]
...                          lzma: [ on  ]
...                     get_cpuid: [ on  ]
...                           bpf: [ on  ]
...                        libaio: [ on  ]
...                       libzstd: [ on  ]
...        disassembler-four-args: [ on  ]
```

This is very confusing because the suggested library (on my Ubuntu 20.04
it is libssl-dev) is already installed. As the test only checks for the
presence of libcrypto, this commit suppresses the deprecation warning to
allow the test to pass.

Signed-off-by: Zixuan Tan <tanzixuan.me@...il.com>
---
 tools/build/feature/test-libcrypto.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/build/feature/test-libcrypto.c b/tools/build/feature/test-libcrypto.c
index a98174e0569c..31afff093d0b 100644
--- a/tools/build/feature/test-libcrypto.c
+++ b/tools/build/feature/test-libcrypto.c
@@ -2,6 +2,12 @@
 #include <openssl/sha.h>
 #include <openssl/md5.h>
 
+/*
+ * The MD5_* API have been deprecated since OpenSSL 3.0, which causes the
+ * feature test to fail silently. This is a workaround.
+ */
+#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
+
 int main(void)
 {
 	MD5_CTX context;
-- 
2.34.1