netdev - [PATCH v4] libbpf: disable SEC pragma macro on GCC

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Date:   Wed,  6 Jul 2022 05:18:38 -0600
From:   James Hilliard <james.hilliard1@...il.com>
To:     bpf@...r.kernel.org
Cc:     James Hilliard <james.hilliard1@...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>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v4] libbpf: disable SEC pragma macro on GCC

It seems the gcc preprocessor breaks with pragmas when surrounding
__attribute__.

Disable these pragmas on GCC due to upstream bugs see:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55578
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90400

Fixes errors like:
error: expected identifier or '(' before '#pragma'
  106 | SEC("cgroup/bind6")
      | ^~~

error: expected '=', ',', ';', 'asm' or '__attribute__' before '#pragma'
  114 | char _license[] SEC("license") = "GPL";
      | ^~~

Signed-off-by: James Hilliard <james.hilliard1@...il.com>
---
Changes v3 -> v4:
  - disable SEC pragmas entirely on GCC
Changes v2 -> v3:
  - just fix SEC pragma
Changes v1 -> v2:
  - replace typeof with __typeof__ instead of changing pragma macros
---
 tools/lib/bpf/bpf_helpers.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
index fb04eaf367f1..7349b16b8e2f 100644
--- a/tools/lib/bpf/bpf_helpers.h
+++ b/tools/lib/bpf/bpf_helpers.h
@@ -22,12 +22,25 @@
  * To allow use of SEC() with externs (e.g., for extern .maps declarations),
  * make sure __attribute__((unused)) doesn't trigger compilation warning.
  */
+#if __GNUC__ && !__clang__
+
+/*
+ * Pragma macros are broken on GCC
+ * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55578
+ * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90400
+ */
+#define SEC(name) __attribute__((section(name), used))
+
+#else
+
 #define SEC(name) \
 	_Pragma("GCC diagnostic push")					    \
 	_Pragma("GCC diagnostic ignored \"-Wignored-attributes\"")	    \
 	__attribute__((section(name), used))				    \
 	_Pragma("GCC diagnostic pop")					    \
 
+#endif
+
 /* Avoid 'linux/stddef.h' definition of '__always_inline'. */
 #undef __always_inline
 #define __always_inline inline __attribute__((always_inline))
-- 
2.34.1