[PATCH bpf-next 1/5] libbpf: call memfd_create() syscall directly

[Andrii Nakryiko <andrii@kernel.org>]

Some versions of Android do not implement memfd_create() wrapper in
their libc implementation, leading to build failures ([0]). On the other
hand, memfd_create() is available as a syscall on quite old kernels
(3.17+, while bpf() syscall itself is available since 3.18+), so it is
ok to assume that syscall availability and call into it with syscall()
helper to avoid Android-specific workarounds.

Validated in libbpf-bootstrap's CI ([1]).

  [0] https://github.com/libbpf/libbpf-bootstrap/actions/runs/7701003207/job/20986080319#step:5:83
  [1] https://github.com/libbpf/libbpf-bootstrap/actions/runs/7715988887/job/21031767212?pr=253

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/lib/bpf/libbpf.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index db65ea59a05a..b21fda6b9b85 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -1525,11 +1525,20 @@ static Elf64_Sym *find_elf_var_sym(const struct bpf_object *obj, const char *nam
 	return ERR_PTR(-ENOENT);
 }
 
+/* Some versions of Android don't provide memfd_create() in their libc
+ * implementation, so avoid complications and just go straight to Linux
+ * syscall.
+ */
+static int sys_memfd_create(const char *name, unsigned flags)
+{
+	return syscall(__NR_memfd_create, name, flags);
+}
+
 static int create_placeholder_fd(void)
 {
 	int fd;
 
-	fd = ensure_good_fd(memfd_create("libbpf-placeholder-fd", MFD_CLOEXEC));
+	fd = ensure_good_fd(sys_memfd_create("libbpf-placeholder-fd", MFD_CLOEXEC));
 	if (fd < 0)
 		return -errno;
 	return fd;
-- 
2.34.1