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

From: Michal Suchanek
Date: Fri Aug 27 2021 - 03:25:54 EST


From: Patrick McCarty <patrick.mccarty@xxxxxxxxx>

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@xxxxxxxxx>
Make the change conditional on GCC version
Signed-off-by: Michal Suchanek <msuchanek@xxxxxxx>
---
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