linux-kernel - [PATCH bpf] libbpf: Fix implicit memfd

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Message-ID: <20250330211325.530677-1-cmllamas@google.com>
Date: Sun, 30 Mar 2025 21:13:23 +0000
From: Carlos Llamas <cmllamas@...gle.com>
To: bpf@...r.kernel.org, Andrii Nakryiko <andrii@...nel.org>, 
	Eduard Zingerman <eddyz87@...il.com>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Alastair Robertson <ajor@...a.com>
Cc: linux-kernel@...r.kernel.org, kernel-team@...roid.com, 
	Carlos Llamas <cmllamas@...gle.com>, Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>
Subject: [PATCH bpf] libbpf: Fix implicit memfd_create() for bionic

Since memfd_create() is not consistently available across different
bionic libc implementations, using memfd_create() directly can break
some Android builds:

  tools/lib/bpf/linker.c:576:7: error: implicit declaration of function 'memfd_create' [-Werror,-Wimplicit-function-declaration]
    576 |         fd = memfd_create(filename, 0);
        |              ^

To fix this, relocate and inline the sys_memfd_create() helper so that
it can be used in "linker.c". Similar issues were previously fixed by
commit 9fa5e1a180aa ("libbpf: Call memfd_create() syscall directly").

Cc: Alastair Robertson <ajor@...a.com>
Cc: Andrii Nakryiko <andrii@...nel.org>
Fixes: 6d5e5e5d7ce1 ("libbpf: Extend linker API to support in-memory ELF files")
Signed-off-by: Carlos Llamas <cmllamas@...gle.com>
---
 tools/lib/bpf/libbpf.c          | 9 ---------
 tools/lib/bpf/libbpf_internal.h | 9 +++++++++
 tools/lib/bpf/linker.c          | 2 +-
 3 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 194809da5172..1f36e16461e1 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -1719,15 +1719,6 @@ 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);
-}
-
 #ifndef MFD_CLOEXEC
 #define MFD_CLOEXEC 0x0001U
 #endif
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index de498e2dd6b0..19770402807f 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -666,6 +666,15 @@ static inline int sys_dup3(int oldfd, int newfd, int flags)
 	return syscall(__NR_dup3, oldfd, newfd, flags);
 }
 
+/* Some versions of Android don't provide memfd_create() in their libc
+ * implementation, so avoid complications and just go straight to Linux
+ * syscall.
+ */
+static inline int sys_memfd_create(const char *name, unsigned flags)
+{
+	return syscall(__NR_memfd_create, name, flags);
+}
+
 /* Point *fixed_fd* to the same file that *tmp_fd* points to.
  * Regardless of success, *tmp_fd* is closed.
  * Whatever *fixed_fd* pointed to is closed silently.
diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
index b52f71c59616..077af6f8bebb 100644
--- a/tools/lib/bpf/linker.c
+++ b/tools/lib/bpf/linker.c
@@ -573,7 +573,7 @@ int bpf_linker__add_buf(struct bpf_linker *linker, void *buf, size_t buf_sz,
 
 	snprintf(filename, sizeof(filename), "mem:%p+%zu", buf, buf_sz);
 
-	fd = memfd_create(filename, 0);
+	fd = sys_memfd_create(filename, 0);
 	if (fd < 0) {
 		ret = -errno;
 		pr_warn("failed to create memfd '%s': %s\n", filename, errstr(ret));
-- 
2.49.0.472.ge94155a9ec-goog