netdev - [PATCH] libbpf: Fix build with latest gcc/binutils with LTO

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Date:   Fri, 27 Aug 2021 09:28:55 +0200
From:   Michal Suchanek <msuchanek@...e.de>
To:     bpf@...r.kernel.org
Cc:     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>,
        Björn Töpel <bjorn@...nel.org>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Patrick McCarty <patrick.mccarty@...el.com>,
        Michal Suchanek <msuchanek@...e.de>
Subject: [PATCH] libbpf: Fix build with latest gcc/binutils with LTO

From: Patrick McCarty <patrick.mccarty@...el.com>

After updating to binutils 2.35, the build began to fail with an
assembler error. A bug was opened on the Red Hat Bugzilla a few days
later for the same issue.

Work around the problem by using the new `symver` attribute (introduced
in GCC 10) as needed, instead of the `COMPAT_VERSION` and
`DEFAULT_VERSION` macros, which expand to assembler directives.

Fixes: https://github.com/libbpf/libbpf/issues/338
Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1863059
Fixes: https://bugzilla.opensuse.org/show_bug.cgi?id=1188749
Signed-off-by: Patrick McCarty <patrick.mccarty@...el.com>
Make the change conditional on GCC version
Signed-off-by: Michal Suchanek <msuchanek@...e.de>
---
 tools/lib/bpf/libbpf_internal.h | 23 +++++++++++++++++------
 tools/lib/bpf/xsk.c             |  4 ++--
 2 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index 016ca7cb4f8a..af0f3fb102c0 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -86,20 +86,31 @@
 	(offsetof(TYPE, FIELD) + sizeof(((TYPE *)0)->FIELD))
 #endif
 
+#ifdef __GNUC__
+# if __GNUC__ >= 10
+#  define DEFAULT_VERSION(internal_name, api_name, version) \
+__attribute__((__symver__(#api_name "@@" #version)))
+#  define COMPAT_VERSION(internal_name, api_name, version) \
+__attribute__((__symver__(#api_name "@" #version)))
+# endif
+#endif
+
+#if !defined(COMPAT_VERSION) || !defined(DEFAULT_VERSION)
 /* Symbol versioning is different between static and shared library.
  * Properly versioned symbols are needed for shared library, but
  * only the symbol of the new version is needed for static library.
  */
-#ifdef SHARED
-# define COMPAT_VERSION(internal_name, api_name, version) \
+# ifdef SHARED
+#  define COMPAT_VERSION(internal_name, api_name, version) \
 	asm(".symver " #internal_name "," #api_name "@" #version);
-# define DEFAULT_VERSION(internal_name, api_name, version) \
+#  define DEFAULT_VERSION(internal_name, api_name, version) \
 	asm(".symver " #internal_name "," #api_name "@@" #version);
-#else
-# define COMPAT_VERSION(internal_name, api_name, version)
-# define DEFAULT_VERSION(internal_name, api_name, version) \
+# else
+#  define COMPAT_VERSION(internal_name, api_name, version)
+#  define DEFAULT_VERSION(internal_name, api_name, version) \
 	extern typeof(internal_name) api_name \
 	__attribute__((alias(#internal_name)));
+# endif
 #endif
 
 extern void libbpf_print(enum libbpf_print_level level,
diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index e9b619aa0cdf..a2111696ba91 100644
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -281,6 +281,7 @@ static int xsk_create_umem_rings(struct xsk_umem *umem, int fd,
 	return err;
 }
 
+DEFAULT_VERSION(xsk_umem__create_v0_0_4, xsk_umem__create, LIBBPF_0.0.4)
 int xsk_umem__create_v0_0_4(struct xsk_umem **umem_ptr, void *umem_area,
 			    __u64 size, struct xsk_ring_prod *fill,
 			    struct xsk_ring_cons *comp,
@@ -345,6 +346,7 @@ struct xsk_umem_config_v1 {
 	__u32 frame_headroom;
 };
 
+COMPAT_VERSION(xsk_umem__create_v0_0_2, xsk_umem__create, LIBBPF_0.0.2)
 int xsk_umem__create_v0_0_2(struct xsk_umem **umem_ptr, void *umem_area,
 			    __u64 size, struct xsk_ring_prod *fill,
 			    struct xsk_ring_cons *comp,
@@ -358,8 +360,6 @@ int xsk_umem__create_v0_0_2(struct xsk_umem **umem_ptr, void *umem_area,
 	return xsk_umem__create_v0_0_4(umem_ptr, umem_area, size, fill, comp,
 					&config);
 }
-COMPAT_VERSION(xsk_umem__create_v0_0_2, xsk_umem__create, LIBBPF_0.0.2)
-DEFAULT_VERSION(xsk_umem__create_v0_0_4, xsk_umem__create, LIBBPF_0.0.4)
 
 static enum xsk_prog get_xsk_prog(void)
 {
-- 
2.31.1