libbpf: Fix build with latest gcc/binutils with LTO

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 assembler directives.

This addresses Red Hat ([0]) and OpenSUSE ([1]) bug reports, as well as libbpf
issue ([2]).

  [0]: https://bugzilla.redhat.com/show_bug.cgi?id=1863059
  [1]: https://bugzilla.opensuse.org/show_bug.cgi?id=1188749
  [2]: Closes: https://github.com/libbpf/libbpf/issues/338

Co-developed-by: Patrick McCarty <patrick.mccarty@intel.com>
Co-developed-by: Michal Suchanek <msuchanek@suse.de>
Signed-off-by: Patrick McCarty <patrick.mccarty@intel.com>
Signed-off-by: Michal Suchanek <msuchanek@suse.de>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210907221023.2660953-1-andrii@kernel.org

CHECKPOINT-COMMIT

@@ -1 +1 @@
-d20b41115ad53293201cc07ee429a38740cb056b
+47bb27a20d6ea22cd092c1fc2bb4fcecac374838

include/uapi/linux/bpf.h

@@ -84,7 +84,7 @@ struct bpf_lpm_trie_key {
 
 struct bpf_cgroup_storage_key {
 	__u64	cgroup_inode_id;	/* cgroup inode id */
-	__u32	attach_type;		/* program attach type */
+	__u32	attach_type;		/* program attach type (enum bpf_attach_type) */
 };
 
 union bpf_iter_link_info {
@@ -4871,6 +4871,12 @@ union bpf_attr {
  * 	Return
  *		Value specified by user at BPF link creation/attachment time
  *		or 0, if it was not specified.
+ *
+ * long bpf_task_pt_regs(struct task_struct *task)
+ *	Description
+ *		Get the struct pt_regs associated with **task**.
+ *	Return
+ *		A pointer to struct pt_regs.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -5048,6 +5054,7 @@ union bpf_attr {
 	FN(timer_cancel),		\
 	FN(get_func_ip),		\
 	FN(get_attach_cookie),		\
+	FN(task_pt_regs),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper

src/bpf_helper_defs.h

@@ -4033,4 +4033,14 @@ static __u64 (*bpf_get_func_ip)(void *ctx) = (void *) 173;
  */
 static __u64 (*bpf_get_attach_cookie)(void *ctx) = (void *) 174;
 
+/*
+ * bpf_task_pt_regs
+ *
+ * 	Get the struct pt_regs associated with **task**.
+ *
+ * Returns
+ * 	A pointer to struct pt_regs.
+ */
+static long (*bpf_task_pt_regs)(struct task_struct *task) = (void *) 175;
+
 

src/libbpf.c

@@ -2993,6 +2993,12 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
 		}
 	}
 
+	if (!obj->efile.symbols) {
+		pr_warn("elf: couldn't find symbol table in %s, stripped object file?\n",
+			obj->path);
+		return -ENOENT;
+	}
+
 	scn = NULL;
 	while ((scn = elf_nextscn(elf, scn)) != NULL) {
 		idx++;

src/libbpf.h

@@ -854,7 +854,7 @@ struct bpf_object_skeleton {
 	size_t sz; /* size of this struct, for forward/backward compatibility */
 
 	const char *name;
-	void *data;
+	const void *data;
 	size_t data_sz;
 
 	struct bpf_object **obj;

src/libbpf_internal.h

@@ -90,17 +90,30 @@
 /* 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.
+ * Starting with GNU C 10, use symver attribute instead of .symver assembler
+ * directive, which works better with GCC LTO builds.
  */
-#ifdef SHARED
+#if defined(SHARED) && defined(__GNUC__) && __GNUC__ >= 10
-# define COMPAT_VERSION(internal_name, api_name, version) \
+
+#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)))
+
+#elif defined(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)
+#else /* !SHARED */
-# define DEFAULT_VERSION(internal_name, api_name, version) \
+
+#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
 
 extern void libbpf_print(enum libbpf_print_level level,

src/xsk.c

@@ -281,6 +281,7 @@ out_mmap:
 	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)
 {

travis-ci/vmtest/configs/blacklist/BLACKLIST-5.5.0

@@ -45,6 +45,7 @@ mmap			# 5.5 kernel is too permissive with re-mmaping
 modify_return		# fmod_ret support is missing
 module_attach		# module BTF support missing (v5.11+)
 netcnt
+netns_cookie		# v5.15+
 ns_current_pid_tgid	# bpf_get_ns_current_pid_tgid() helper is missing
 pe_preserve_elems	# v5.10+
 perf_branches		# bpf_read_branch_records() helper is missing
@@ -74,10 +75,12 @@ socket_cookie		# v5.12+
 sockmap_basic		# uses new socket fields, 5.8+
 sockmap_listen		# no listen socket supportin SOCKMAP
 sockopt_sk
+sockopt_qos_to_cc	# v5.15+
 stacktrace_build_id	# v5.9+
 stack_var_off		# v5.12+
 syscall			# v5.14+
 task_local_storage	# v5.12+
+task_pt_regs		# v5.15+
 tcp_hdr_options		# v5.10+, new TCP header options feature in BPF
 tcpbpf_user		# LINK_CREATE is missing
 tc_redirect		# v5.14+

travis-ci/vmtest/run.sh

@@ -459,10 +459,10 @@ if kvm-ok ; then
 else
   accel="-cpu qemu64 -machine accel=tcg"
 fi
-qemu-system-x86_64 -nodefaults -display none -serial mon:stdio \
+qemu-system-x86_64 -nodefaults -display none -serial mon:stdio -no-reboot \
   ${accel} -smp "$(nproc)" -m 4G \
   -drive file="$IMG",format=raw,index=1,media=disk,if=virtio,cache=none \
-  -kernel "$vmlinuz" -append "root=/dev/vda rw console=ttyS0,115200$APPEND"
+  -kernel "$vmlinuz" -append "root=/dev/vda rw console=ttyS0,115200 kernel.panic=-1 $APPEND"
 sudo mount -o loop "$IMG" "$mnt"
 if exitstatus="$(cat "$mnt/exitstatus" 2>/dev/null)"; then
 	printf '\nTests exit status: %s\n' "$exitstatus" >&2