[libc-commits] [libc] [libc] Implement the linux-specific memfd_create syscall wrapper (PR #197439)
via libc-commits
libc-commits at lists.llvm.org
Wed May 13 06:28:00 PDT 2026
llvmorg-github-actions[bot] wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-backend-risc-v
Author: Pavel Labath (labath)
<details>
<summary>Changes</summary>
I'm using the MFD constants from the kernel header as that's what was done for mmap, though it would be relatively simple to declare these ourselves, as they are not architecture-dependent.
---
Full diff: https://github.com/llvm/llvm-project/pull/197439.diff
14 Files Affected:
- (modified) libc/config/linux/aarch64/entrypoints.txt (+1)
- (modified) libc/config/linux/arm/entrypoints.txt (+1)
- (modified) libc/config/linux/riscv/entrypoints.txt (+1)
- (modified) libc/config/linux/x86_64/entrypoints.txt (+1)
- (modified) libc/include/llvm-libc-macros/sys-mman-macros.h (+4)
- (modified) libc/include/sys/mman.yaml (+7)
- (modified) libc/src/__support/OSUtil/linux/syscall_wrappers/CMakeLists.txt (+12)
- (added) libc/src/__support/OSUtil/linux/syscall_wrappers/memfd_create.h (+36)
- (modified) libc/src/sys/mman/CMakeLists.txt (+7)
- (modified) libc/src/sys/mman/linux/CMakeLists.txt (+11)
- (added) libc/src/sys/mman/linux/memfd_create.cpp (+31)
- (added) libc/src/sys/mman/memfd_create.h (+25)
- (modified) libc/test/src/sys/mman/linux/CMakeLists.txt (+21)
- (added) libc/test/src/sys/mman/linux/memfd_create_test.cpp (+48)
``````````diff
diff --git a/libc/config/linux/aarch64/entrypoints.txt b/libc/config/linux/aarch64/entrypoints.txt
index e62bc67e2d5ca..f7e40c1a142fe 100644
--- a/libc/config/linux/aarch64/entrypoints.txt
+++ b/libc/config/linux/aarch64/entrypoints.txt
@@ -256,6 +256,7 @@ set(TARGET_LIBC_ENTRYPOINTS
# sys/mman.h entrypoints
libc.src.sys.mman.madvise
+ libc.src.sys.mman.memfd_create
libc.src.sys.mman.mincore
libc.src.sys.mman.mlock
libc.src.sys.mman.mlock2
diff --git a/libc/config/linux/arm/entrypoints.txt b/libc/config/linux/arm/entrypoints.txt
index 1c4dd1a4cb879..906f36d45e337 100644
--- a/libc/config/linux/arm/entrypoints.txt
+++ b/libc/config/linux/arm/entrypoints.txt
@@ -177,6 +177,7 @@ set(TARGET_LIBC_ENTRYPOINTS
libc.src.sys.ioctl.ioctl
# sys/mman.h entrypoints
+ libc.src.sys.mman.memfd_create
libc.src.sys.mman.mmap
libc.src.sys.mman.munmap
diff --git a/libc/config/linux/riscv/entrypoints.txt b/libc/config/linux/riscv/entrypoints.txt
index d1c52dffdb6e7..bf2fb014f4f77 100644
--- a/libc/config/linux/riscv/entrypoints.txt
+++ b/libc/config/linux/riscv/entrypoints.txt
@@ -256,6 +256,7 @@ set(TARGET_LIBC_ENTRYPOINTS
# sys/mman.h entrypoints
libc.src.sys.mman.madvise
+ libc.src.sys.mman.memfd_create
libc.src.sys.mman.mincore
libc.src.sys.mman.mlock
libc.src.sys.mman.mlock2
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 73b4b3fcd191f..2a6a79cfa77de 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -262,6 +262,7 @@ set(TARGET_LIBC_ENTRYPOINTS
# sys/mman.h entrypoints
libc.src.sys.mman.madvise
+ libc.src.sys.mman.memfd_create
libc.src.sys.mman.mincore
libc.src.sys.mman.mlock
libc.src.sys.mman.mlock2
diff --git a/libc/include/llvm-libc-macros/sys-mman-macros.h b/libc/include/llvm-libc-macros/sys-mman-macros.h
index a6dc6d96b5b79..bc9f783d84a40 100644
--- a/libc/include/llvm-libc-macros/sys-mman-macros.h
+++ b/libc/include/llvm-libc-macros/sys-mman-macros.h
@@ -18,6 +18,10 @@
#error "cannot use <sys/mman.h> without proper system headers."
#endif
+#if __has_include(<linux/memfd.h>)
+#include <linux/memfd.h>
+#endif
+
// Some posix standard flags may not be defined in system headers.
// Posix mmap flags.
#ifndef MAP_FAILED
diff --git a/libc/include/sys/mman.yaml b/libc/include/sys/mman.yaml
index 6adc2c2d5bfa6..f14a90436b791 100644
--- a/libc/include/sys/mman.yaml
+++ b/libc/include/sys/mman.yaml
@@ -19,6 +19,13 @@ functions:
- type: void *
- type: size_t
- type: int
+ - name: memfd_create
+ standards:
+ - Linux
+ return_type: int
+ arguments:
+ - type: const char *
+ - type: unsigned int
- name: mincore
standards:
- Linux
diff --git a/libc/src/__support/OSUtil/linux/syscall_wrappers/CMakeLists.txt b/libc/src/__support/OSUtil/linux/syscall_wrappers/CMakeLists.txt
index bbe76fece3bdd..8d0acca011bec 100644
--- a/libc/src/__support/OSUtil/linux/syscall_wrappers/CMakeLists.txt
+++ b/libc/src/__support/OSUtil/linux/syscall_wrappers/CMakeLists.txt
@@ -198,6 +198,18 @@ add_header_library(
libc.include.sys_syscall
)
+add_header_library(
+ memfd_create
+ HDRS
+ memfd_create.h
+ DEPENDS
+ libc.src.__support.OSUtil.osutil
+ libc.src.__support.common
+ libc.src.__support.error_or
+ libc.src.__support.macros.config
+ libc.include.sys_syscall
+)
+
add_header_library(
mmap
HDRS
diff --git a/libc/src/__support/OSUtil/linux/syscall_wrappers/memfd_create.h b/libc/src/__support/OSUtil/linux/syscall_wrappers/memfd_create.h
new file mode 100644
index 0000000000000..e748c3c6fb80d
--- /dev/null
+++ b/libc/src/__support/OSUtil/linux/syscall_wrappers/memfd_create.h
@@ -0,0 +1,36 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// ErrorOr-returning syscall wrapper for memfd_create.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_MEMFD_CREATE_H
+#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_MEMFD_CREATE_H
+
+#include "src/__support/OSUtil/linux/syscall.h" // syscall_impl
+#include "src/__support/common.h"
+#include "src/__support/error_or.h"
+#include "src/__support/macros/config.h"
+#include <sys/syscall.h> // For syscall numbers
+
+namespace LIBC_NAMESPACE_DECL {
+namespace linux_syscalls {
+
+LIBC_INLINE ErrorOr<int> memfd_create(const char *name, unsigned int flags) {
+ int ret = syscall_impl<int>(SYS_memfd_create, name, flags);
+ if (ret < 0)
+ return Error(-ret);
+ return ret;
+}
+
+} // namespace linux_syscalls
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_MEMFD_CREATE_H
diff --git a/libc/src/sys/mman/CMakeLists.txt b/libc/src/sys/mman/CMakeLists.txt
index c7be1eddacb5e..ca18fe36449da 100644
--- a/libc/src/sys/mman/CMakeLists.txt
+++ b/libc/src/sys/mman/CMakeLists.txt
@@ -9,6 +9,13 @@ add_entrypoint_object(
.${LIBC_TARGET_OS}.madvise
)
+add_entrypoint_object(
+ memfd_create
+ ALIAS
+ DEPENDS
+ .${LIBC_TARGET_OS}.memfd_create
+)
+
add_entrypoint_object(
mmap
ALIAS
diff --git a/libc/src/sys/mman/linux/CMakeLists.txt b/libc/src/sys/mman/linux/CMakeLists.txt
index 6cafa9ba45c1a..e8d9ed384c9b0 100644
--- a/libc/src/sys/mman/linux/CMakeLists.txt
+++ b/libc/src/sys/mman/linux/CMakeLists.txt
@@ -18,6 +18,17 @@ add_entrypoint_object(
libc.src.errno.errno
)
+add_entrypoint_object(
+ memfd_create
+ SRCS
+ memfd_create.cpp
+ HDRS
+ ../memfd_create.h
+ DEPENDS
+ libc.src.__support.OSUtil.linux.syscall_wrappers.memfd_create
+ libc.src.errno.errno
+)
+
add_entrypoint_object(
mmap
SRCS
diff --git a/libc/src/sys/mman/linux/memfd_create.cpp b/libc/src/sys/mman/linux/memfd_create.cpp
new file mode 100644
index 0000000000000..e3e1e00034e1a
--- /dev/null
+++ b/libc/src/sys/mman/linux/memfd_create.cpp
@@ -0,0 +1,31 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Linux implementation of the memfd_create function.
+///
+//===----------------------------------------------------------------------===//
+
+#include "src/sys/mman/memfd_create.h"
+#include "src/__support/OSUtil/linux/syscall_wrappers/memfd_create.h"
+#include "src/__support/common.h"
+#include "src/__support/libc_errno.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, memfd_create, (const char *name, unsigned int flags)) {
+ ErrorOr<int> result = linux_syscalls::memfd_create(name, flags);
+ if (!result) {
+ libc_errno = result.error();
+ return -1;
+ }
+ return result.value();
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/sys/mman/memfd_create.h b/libc/src/sys/mman/memfd_create.h
new file mode 100644
index 0000000000000..eefdae3e29d7e
--- /dev/null
+++ b/libc/src/sys/mman/memfd_create.h
@@ -0,0 +1,25 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Implementation header for memfd_create function.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SYS_MMAN_MEMFD_CREATE_H
+#define LLVM_LIBC_SRC_SYS_MMAN_MEMFD_CREATE_H
+
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int memfd_create(const char *name, unsigned int flags);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_SYS_MMAN_MEMFD_CREATE_H
diff --git a/libc/test/src/sys/mman/linux/CMakeLists.txt b/libc/test/src/sys/mman/linux/CMakeLists.txt
index b73212d0c322f..29d97cbfe7018 100644
--- a/libc/test/src/sys/mman/linux/CMakeLists.txt
+++ b/libc/test/src/sys/mman/linux/CMakeLists.txt
@@ -229,3 +229,24 @@ add_libc_unittest(
libc.test.UnitTest.ErrnoCheckingTest
libc.test.UnitTest.ErrnoSetterMatcher
)
+
+add_libc_unittest(
+ memfd_create_test
+ SUITE
+ libc_sys_mman_unittests
+ SRCS
+ memfd_create_test.cpp
+ DEPENDS
+ libc.hdr.fcntl_macros
+ libc.hdr.sys_mman_macros
+ libc.include.llvm-libc-macros.file_seek_macros
+ libc.include.sys_mman
+ libc.src.__support.CPP.scope
+ libc.src.errno.errno
+ libc.src.fcntl.fcntl
+ libc.src.sys.mman.memfd_create
+ libc.src.unistd.close
+ libc.src.unistd.lseek
+ libc.test.UnitTest.ErrnoCheckingTest
+ libc.test.UnitTest.ErrnoSetterMatcher
+)
diff --git a/libc/test/src/sys/mman/linux/memfd_create_test.cpp b/libc/test/src/sys/mman/linux/memfd_create_test.cpp
new file mode 100644
index 0000000000000..13c1c920e4009
--- /dev/null
+++ b/libc/test/src/sys/mman/linux/memfd_create_test.cpp
@@ -0,0 +1,48 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Unittests for memfd_create.
+///
+//===----------------------------------------------------------------------===//
+
+#include "hdr/fcntl_macros.h"
+#include "hdr/sys_mman_macros.h"
+#include "include/llvm-libc-macros/file-seek-macros.h"
+#include "src/__support/CPP/scope.h"
+#include "src/fcntl/fcntl.h"
+#include "src/sys/mman/memfd_create.h"
+#include "src/unistd/close.h"
+#include "src/unistd/lseek.h"
+#include "test/UnitTest/ErrnoCheckingTest.h"
+#include "test/UnitTest/ErrnoSetterMatcher.h"
+#include "test/UnitTest/Test.h"
+
+using namespace LIBC_NAMESPACE::testing::ErrnoSetterMatcher;
+using LlvmLibcMemfdCreateTest = LIBC_NAMESPACE::testing::ErrnoCheckingTest;
+
+TEST_F(LlvmLibcMemfdCreateTest, Basic) {
+ int fd;
+ ASSERT_THAT(fd = LIBC_NAMESPACE::memfd_create("test_memfd", MFD_CLOEXEC),
+ returns(GE(0)).with_errno(EQ(0)));
+ LIBC_NAMESPACE::cpp::scope_exit close_fd(
+ [&] { ASSERT_THAT(LIBC_NAMESPACE::close(fd), Succeeds(0)); });
+
+ int flag;
+ ASSERT_THAT(flag = LIBC_NAMESPACE::fcntl(fd, F_GETFD),
+ returns(GE(0)).with_errno(EQ(0)));
+ EXPECT_NE(flag & FD_CLOEXEC, 0);
+
+ ASSERT_THAT(LIBC_NAMESPACE::lseek(fd, 0, SEEK_END), Succeeds(off_t(0)));
+}
+
+TEST_F(LlvmLibcMemfdCreateTest, ErrorHandling) {
+ // Passing invalid flags should cause EINVAL
+ ASSERT_THAT(LIBC_NAMESPACE::memfd_create("test_memfd", 0x80000000),
+ Fails(EINVAL));
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/197439
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