tools lib bpf: Provide wrapper for strerror_r to build in !_GNU_SOURCE systems

Same problem that got fixed in a similar fashion in tools/perf/ in
c8b5f2c96d1b ("tools: Introduce str_error_r()"), fix it in the same
way, licensing needs to be sorted out to libbpf to use libapi, so,
for this simple case, just get the same wrapper in tools/lib/bpf.

This makes libbpf and its users (bpftool, selftests, perf) to build
again in Alpine Linux 3.[45678] and edge.

Acked-by: Alexei Starovoitov <ast@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David Ahern <dsahern@gmail.com>
Cc: Hendrik Brueckner <brueckner@linux.ibm.com>
Cc: Jakub Kicinski <jakub.kicinski@netronome.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Martin KaFai Lau <kafai@fb.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Quentin Monnet <quentin.monnet@netronome.com>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: Yonghong Song <yhs@fb.com>
Fixes: 1ce6a9fc1549 ("bpf: fix build error in libbpf with EXTRA_CFLAGS="-Wp, -D_FORTIFY_SOURCE=2 -O2"")
Link: https://lkml.kernel.org/r/20180917151636.GA21790@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

4 files changed, 35 insertions, 11 deletions

diff --git a/tools/lib/bpf/Build b/tools/lib/bpf/Build
index 13a861135127..6eb9bacd1948 100644
--- a/tools/lib/bpf/Build
+++ b/tools/lib/bpf/Build
@@ -1 +1 @@
-libbpf-y := libbpf.o bpf.o nlattr.o btf.o libbpf_errno.o
+libbpf-y := libbpf.o bpf.o nlattr.o btf.o libbpf_errno.o str_error.o
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 2abd0f112627..bdb94939fd60 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -50,6 +50,7 @@
 #include "libbpf.h"
 #include "bpf.h"
 #include "btf.h"
+#include "str_error.h"
 
 #ifndef EM_BPF
 #define EM_BPF 247
@@ -469,7 +470,7 @@ static int bpf_object__elf_init(struct bpf_object *obj)
                 obj->efile.fd = open(obj->path, O_RDONLY);
                 if (obj->efile.fd < 0) {
                         char errmsg[STRERR_BUFSIZE];
-                        char *cp = strerror_r(errno, errmsg, sizeof(errmsg));
+                        char *cp = str_error(errno, errmsg, sizeof(errmsg));
 
                         pr_warning("failed to open %s: %s\n", obj->path, cp);
                         return -errno;
@@ -810,8 +811,7 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
                                                       data->d_size, name, idx);
                         if (err) {
                                 char errmsg[STRERR_BUFSIZE];
-                                char *cp = strerror_r(-err, errmsg,
-                                                      sizeof(errmsg));
+                                char *cp = str_error(-err, errmsg, sizeof(errmsg));
 
                                 pr_warning("failed to alloc program %s (%s): %s",
                                            name, obj->path, cp);
@@ -1140,7 +1140,7 @@ bpf_object__create_maps(struct bpf_object *obj)
 
                 *pfd = bpf_create_map_xattr(&create_attr);
                 if (*pfd < 0 && create_attr.btf_key_type_id) {
-                        cp = strerror_r(errno, errmsg, sizeof(errmsg));
+                        cp = str_error(errno, errmsg, sizeof(errmsg));
                         pr_warning("Error in bpf_create_map_xattr(%s):%s(%d). Retrying without BTF.\n",
                                    map->name, cp, errno);
                         create_attr.btf_fd = 0;
@@ -1155,7 +1155,7 @@ bpf_object__create_maps(struct bpf_object *obj)
                         size_t j;
 
                         err = *pfd;
-                        cp = strerror_r(errno, errmsg, sizeof(errmsg));
+                        cp = str_error(errno, errmsg, sizeof(errmsg));
                         pr_warning("failed to create map (name: '%s'): %s\n",
                                    map->name, cp);
                         for (j = 0; j < i; j++)
@@ -1339,7 +1339,7 @@ load_program(enum bpf_prog_type type, enum bpf_attach_type expected_attach_type,
         }
 
         ret = -LIBBPF_ERRNO__LOAD;
-        cp = strerror_r(errno, errmsg, sizeof(errmsg));
+        cp = str_error(errno, errmsg, sizeof(errmsg));
         pr_warning("load bpf program failed: %s\n", cp);
 
         if (log_buf && log_buf[0] != '\0') {
@@ -1654,7 +1654,7 @@ static int check_path(const char *path)
 
         dir = dirname(dname);
         if (statfs(dir, &st_fs)) {
-                cp = strerror_r(errno, errmsg, sizeof(errmsg));
+                cp = str_error(errno, errmsg, sizeof(errmsg));
                 pr_warning("failed to statfs %s: %s\n", dir, cp);
                 err = -errno;
         }
@@ -1690,7 +1690,7 @@ int bpf_program__pin_instance(struct bpf_program *prog, const char *path,
         }
 
         if (bpf_obj_pin(prog->instances.fds[instance], path)) {
-                cp = strerror_r(errno, errmsg, sizeof(errmsg));
+                cp = str_error(errno, errmsg, sizeof(errmsg));
                 pr_warning("failed to pin program: %s\n", cp);
                 return -errno;
         }
@@ -1708,7 +1708,7 @@ static int make_dir(const char *path)
                 err = -errno;
 
         if (err) {
-                cp = strerror_r(-err, errmsg, sizeof(errmsg));
+                cp = str_error(-err, errmsg, sizeof(errmsg));
                 pr_warning("failed to mkdir %s: %s\n", path, cp);
         }
         return err;
@@ -1770,7 +1770,7 @@ int bpf_map__pin(struct bpf_map *map, const char *path)
         }
 
         if (bpf_obj_pin(map->fd, path)) {
-                cp = strerror_r(errno, errmsg, sizeof(errmsg));
+                cp = str_error(errno, errmsg, sizeof(errmsg));
                 pr_warning("failed to pin map: %s\n", cp);
                 return -errno;
         }
diff --git a/tools/lib/bpf/str_error.c b/tools/lib/bpf/str_error.c
new file mode 100644
index 000000000000..b8798114a357
--- /dev/null
+++ b/tools/lib/bpf/str_error.c
@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: LGPL-2.1
+#undef _GNU_SOURCE
+#include <string.h>
+#include <stdio.h>
+#include "str_error.h"
+
+/*
+ * Wrapper to allow for building in non-GNU systems such as Alpine Linux's musl
+ * libc, while checking strerror_r() return to avoid having to check this in
+ * all places calling it.
+ */
+char *str_error(int err, char *dst, int len)
+{
+        int ret = strerror_r(err, dst, len);
+        if (ret)
+                snprintf(dst, len, "ERROR: strerror_r(%d)=%d", err, ret);
+        return dst;
+}
diff --git a/tools/lib/bpf/str_error.h b/tools/lib/bpf/str_error.h
new file mode 100644
index 000000000000..355b1db571d1
--- /dev/null
+++ b/tools/lib/bpf/str_error.h
@@ -0,0 +1,6 @@
+// SPDX-License-Identifier: LGPL-2.1
+#ifndef BPF_STR_ERROR
+#define BPF_STR_ERROR
+
+char *str_error(int err, char *dst, int len);
+#endif // BPF_STR_ERROR