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libbpf: Fix implicit memfd_create() for bionic

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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").

Fixes: 6d5e5e5d7ce1 ("libbpf: Extend linker API to support in-memory ELF files")
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250330211325.530677-1-cmllamas@google.com
This commit is contained in:
Carlos Llamas
2025-03-30 21:13:23 +00:00
committed by Andrii Nakryiko
parent 4659eaafa4
commit 732d6c011f
3 changed files with 10 additions and 10 deletions
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9
src/libbpf.c
View File

@@ -1725,15 +1725,6 @@ 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

9
src/libbpf_internal.h
View File

@@ -667,6 +667,15 @@ 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.

2
src/linker.c
View File

@@ -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));