[libc-commits] [libc] 8989aa0 - [libc] Add POSIX functions dup, dup2, and GNU extension function dup3.
Siva Chandra Reddy via libc-commits
libc-commits at lists.llvm.org
Tue Sep 13 11:06:41 PDT 2022
Author: Siva Chandra Reddy
Date: 2022-09-13T18:06:30Z
New Revision: 8989aa003f3d33498801e3a41871472da1bc211e
URL: https://github.com/llvm/llvm-project/commit/8989aa003f3d33498801e3a41871472da1bc211e
DIFF: https://github.com/llvm/llvm-project/commit/8989aa003f3d33498801e3a41871472da1bc211e.diff
LOG: [libc] Add POSIX functions dup, dup2, and GNU extension function dup3.
Reviewed By: lntue
Differential Revision: https://reviews.llvm.org/D133748
Added:
libc/src/unistd/dup.h
libc/src/unistd/dup2.h
libc/src/unistd/dup3.h
libc/src/unistd/linux/dup.cpp
libc/src/unistd/linux/dup2.cpp
libc/src/unistd/linux/dup3.cpp
libc/test/src/unistd/dup2_test.cpp
libc/test/src/unistd/dup3_test.cpp
libc/test/src/unistd/dup_test.cpp
Modified:
libc/config/linux/aarch64/entrypoints.txt
libc/config/linux/x86_64/entrypoints.txt
libc/include/llvm-libc-macros/linux/fcntl-macros.h
libc/spec/gnu_ext.td
libc/spec/posix.td
libc/src/unistd/CMakeLists.txt
libc/src/unistd/linux/CMakeLists.txt
libc/test/src/unistd/CMakeLists.txt
Removed:
################################################################################
diff --git a/libc/config/linux/aarch64/entrypoints.txt b/libc/config/linux/aarch64/entrypoints.txt
index fc64f1ee94062..adb4602cbfe2b 100644
--- a/libc/config/linux/aarch64/entrypoints.txt
+++ b/libc/config/linux/aarch64/entrypoints.txt
@@ -113,6 +113,9 @@ set(TARGET_LIBC_ENTRYPOINTS
# unistd.h entrypoints
libc.src.unistd.chdir
libc.src.unistd.close
+ libc.src.unistd.dup
+ libc.src.unistd.dup2
+ libc.src.unistd.dup3
libc.src.unistd.fchdir
libc.src.unistd.fsync
libc.src.unistd.ftruncate
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index b1fb34cafc4c0..bd384637122e2 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -113,6 +113,9 @@ set(TARGET_LIBC_ENTRYPOINTS
# unistd.h entrypoints
libc.src.unistd.chdir
libc.src.unistd.close
+ libc.src.unistd.dup
+ libc.src.unistd.dup2
+ libc.src.unistd.dup3
libc.src.unistd.fchdir
libc.src.unistd.fsync
libc.src.unistd.ftruncate
diff --git a/libc/include/llvm-libc-macros/linux/fcntl-macros.h b/libc/include/llvm-libc-macros/linux/fcntl-macros.h
index 6f30330f3a457..92e4568e61a22 100644
--- a/libc/include/llvm-libc-macros/linux/fcntl-macros.h
+++ b/libc/include/llvm-libc-macros/linux/fcntl-macros.h
@@ -70,4 +70,11 @@
// has to perform the equivalent of "rmdir" on the path argument.
#define AT_REMOVEDIR 0x200
+// Values of SYS_fcntl commands.
+#define F_DUPFD 0
+#define F_GETFD 1
+#define F_SETFD 2
+#define F_GETFL 3
+#define F_SETFL 4
+
#endif // __LLVM_LIBC_MACROS_LINUX_FCNTL_MACROS_H
diff --git a/libc/spec/gnu_ext.td b/libc/spec/gnu_ext.td
index c1f08af138146..d75d6e6a2c57d 100644
--- a/libc/spec/gnu_ext.td
+++ b/libc/spec/gnu_ext.td
@@ -144,6 +144,20 @@ def GnuExtensions : StandardSpec<"GNUExtensions"> {
]
>;
+ HeaderSpec UniStd = HeaderSpec<
+ "unistd.h",
+ [], // Macros
+ [], // Types
+ [], // Enumerations
+ [
+ FunctionSpec<
+ "dup2",
+ RetValSpec<IntType>,
+ [ArgSpec<IntType>, ArgSpec<IntType>, ArgSpec<IntType>]
+ >,
+ ]
+ >;
+
let Headers = [
CType,
FEnv,
@@ -152,5 +166,6 @@ def GnuExtensions : StandardSpec<"GNUExtensions"> {
SendFile,
StdIO,
String,
+ UniStd,
];
}
diff --git a/libc/spec/posix.td b/libc/spec/posix.td
index 4dcf09dda7e0d..12dc68b65dc39 100644
--- a/libc/spec/posix.td
+++ b/libc/spec/posix.td
@@ -266,6 +266,21 @@ def POSIX : StandardSpec<"POSIX"> {
RetValSpec<IntType>,
[ArgSpec<ConstCharPtr>]
>,
+ FunctionSpec<
+ "dup",
+ RetValSpec<IntType>,
+ [ArgSpec<IntType>]
+ >,
+ FunctionSpec<
+ "dup2",
+ RetValSpec<IntType>,
+ [ArgSpec<IntType>, ArgSpec<IntType>]
+ >,
+ FunctionSpec<
+ "dup3",
+ RetValSpec<IntType>,
+ [ArgSpec<IntType>, ArgSpec<IntType>, ArgSpec<IntType>]
+ >,
FunctionSpec<
"fchdir",
RetValSpec<IntType>,
diff --git a/libc/src/unistd/CMakeLists.txt b/libc/src/unistd/CMakeLists.txt
index d55ed7163ca44..f03a1ac7b7a03 100644
--- a/libc/src/unistd/CMakeLists.txt
+++ b/libc/src/unistd/CMakeLists.txt
@@ -16,6 +16,27 @@ add_entrypoint_object(
.${LIBC_TARGET_OS}.close
)
+add_entrypoint_object(
+ dup
+ ALIAS
+ DEPENDS
+ .${LIBC_TARGET_OS}.dup
+)
+
+add_entrypoint_object(
+ dup2
+ ALIAS
+ DEPENDS
+ .${LIBC_TARGET_OS}.dup2
+)
+
+add_entrypoint_object(
+ dup3
+ ALIAS
+ DEPENDS
+ .${LIBC_TARGET_OS}.dup3
+)
+
add_entrypoint_object(
fchdir
ALIAS
diff --git a/libc/src/unistd/dup.h b/libc/src/unistd/dup.h
new file mode 100644
index 0000000000000..21b358251ea91
--- /dev/null
+++ b/libc/src/unistd/dup.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for dup ---------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_UNISTD_DUP_H
+#define LLVM_LIBC_SRC_UNISTD_DUP_H
+
+#include <unistd.h>
+
+namespace __llvm_libc {
+
+int dup(int fd);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_UNISTD_DUP_H
diff --git a/libc/src/unistd/dup2.h b/libc/src/unistd/dup2.h
new file mode 100644
index 0000000000000..39e4da8c19fbb
--- /dev/null
+++ b/libc/src/unistd/dup2.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for dup2 --------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_UNISTD_DUP2_H
+#define LLVM_LIBC_SRC_UNISTD_DUP2_H
+
+#include <unistd.h>
+
+namespace __llvm_libc {
+
+int dup2(int oldfd, int newfd);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_UNISTD_DUP2_H
diff --git a/libc/src/unistd/dup3.h b/libc/src/unistd/dup3.h
new file mode 100644
index 0000000000000..c7e107071b7da
--- /dev/null
+++ b/libc/src/unistd/dup3.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for dup3 --------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_UNISTD_DUP3_H
+#define LLVM_LIBC_SRC_UNISTD_DUP3_H
+
+#include <unistd.h>
+
+namespace __llvm_libc {
+
+int dup3(int oldfd, int newfd, int flags);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_UNISTD_DUP3_H
diff --git a/libc/src/unistd/linux/CMakeLists.txt b/libc/src/unistd/linux/CMakeLists.txt
index 249b057ca950d..812c7ef7a60ee 100644
--- a/libc/src/unistd/linux/CMakeLists.txt
+++ b/libc/src/unistd/linux/CMakeLists.txt
@@ -24,6 +24,46 @@ add_entrypoint_object(
libc.src.errno.errno
)
+add_entrypoint_object(
+ dup
+ SRCS
+ dup.cpp
+ HDRS
+ ../dup.h
+ DEPENDS
+ libc.include.unistd
+ libc.include.sys_syscall
+ libc.src.__support.OSUtil.osutil
+ libc.src.errno.errno
+)
+
+add_entrypoint_object(
+ dup2
+ SRCS
+ dup2.cpp
+ HDRS
+ ../dup2.h
+ DEPENDS
+ libc.include.fcntl
+ libc.include.unistd
+ libc.include.sys_syscall
+ libc.src.__support.OSUtil.osutil
+ libc.src.errno.errno
+)
+
+add_entrypoint_object(
+ dup3
+ SRCS
+ dup3.cpp
+ HDRS
+ ../dup3.h
+ DEPENDS
+ libc.include.unistd
+ libc.include.sys_syscall
+ libc.src.__support.OSUtil.osutil
+ libc.src.errno.errno
+)
+
add_entrypoint_object(
fchdir
SRCS
diff --git a/libc/src/unistd/linux/dup.cpp b/libc/src/unistd/linux/dup.cpp
new file mode 100644
index 0000000000000..9706b98897a80
--- /dev/null
+++ b/libc/src/unistd/linux/dup.cpp
@@ -0,0 +1,28 @@
+//===-- Linux implementation of dup ---------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/unistd/dup.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+
+#include <errno.h>
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, dup, (int fd)) {
+ long ret = __llvm_libc::syscall(SYS_dup, fd);
+ if (ret < 0) {
+ errno = -ret;
+ return -1;
+ }
+ return ret;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/unistd/linux/dup2.cpp b/libc/src/unistd/linux/dup2.cpp
new file mode 100644
index 0000000000000..e066a7c471692
--- /dev/null
+++ b/libc/src/unistd/linux/dup2.cpp
@@ -0,0 +1,47 @@
+//===-- Linux implementation of dup2 --------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/unistd/dup2.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, dup2, (int oldfd, int newfd)) {
+#ifdef SYS_dup2
+ // If dup2 syscall is available, we make use of directly.
+ long ret = __llvm_libc::syscall(SYS_dup2, oldfd, newfd);
+#elif defined(SYS_dup3)
+ // If dup2 syscall is not available, we try using the dup3 syscall. However,
+ // dup3 fails if oldfd is the same as newfd. So, we handle that case
+ // separately before making the dup3 syscall.
+ if (oldfd == newfd) {
+ // Check if oldfd is actually a valid file descriptor.
+ long ret = __llvm_libc::syscall(SYS_fcntl, oldfd, F_GETFD);
+ if (ret >= 0)
+ return oldfd;
+ errno = -ret;
+ return -1;
+ }
+ long ret = __llvm_libc::syscall(SYS_dup3, oldfd, newfd, 0);
+#else
+#error "SYS_dup2 and SYS_dup3 not available for the target."
+#endif
+ if (ret < 0) {
+ errno = -ret;
+ return -1;
+ }
+ return ret;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/unistd/linux/dup3.cpp b/libc/src/unistd/linux/dup3.cpp
new file mode 100644
index 0000000000000..193ff3e278dd8
--- /dev/null
+++ b/libc/src/unistd/linux/dup3.cpp
@@ -0,0 +1,28 @@
+//===-- Linux implementation of dup3 --------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/unistd/dup3.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+
+#include <errno.h>
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, dup3, (int oldfd, int newfd, int flags)) {
+ // If dup2 syscall is available, we make use of directly.
+ long ret = __llvm_libc::syscall(SYS_dup3, oldfd, newfd, flags);
+ if (ret >= 0)
+ return ret;
+ errno = -ret;
+ return -1;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/test/src/unistd/CMakeLists.txt b/libc/test/src/unistd/CMakeLists.txt
index 1ea5fcfbbebc7..9ac884ccff271 100644
--- a/libc/test/src/unistd/CMakeLists.txt
+++ b/libc/test/src/unistd/CMakeLists.txt
@@ -17,6 +17,60 @@ add_libc_unittest(
libc.test.errno_setter_matcher
)
+add_libc_unittest(
+ dup_test
+ SUITE
+ libc_unistd_unittests
+ SRCS
+ dup_test.cpp
+ DEPENDS
+ libc.include.errno
+ libc.include.unistd
+ libc.src.fcntl.open
+ libc.src.unistd.close
+ libc.src.unistd.dup
+ libc.src.unistd.read
+ libc.src.unistd.unlink
+ libc.src.unistd.write
+ libc.test.errno_setter_matcher
+)
+
+add_libc_unittest(
+ dup2_test
+ SUITE
+ libc_unistd_unittests
+ SRCS
+ dup2_test.cpp
+ DEPENDS
+ libc.include.errno
+ libc.include.unistd
+ libc.src.fcntl.open
+ libc.src.unistd.close
+ libc.src.unistd.dup2
+ libc.src.unistd.read
+ libc.src.unistd.unlink
+ libc.src.unistd.write
+ libc.test.errno_setter_matcher
+)
+
+add_libc_unittest(
+ dup3_test
+ SUITE
+ libc_unistd_unittests
+ SRCS
+ dup3_test.cpp
+ DEPENDS
+ libc.include.errno
+ libc.include.unistd
+ libc.src.fcntl.open
+ libc.src.unistd.close
+ libc.src.unistd.dup3
+ libc.src.unistd.read
+ libc.src.unistd.unlink
+ libc.src.unistd.write
+ libc.test.errno_setter_matcher
+)
+
add_libc_unittest(
fchdir_test
SUITE
diff --git a/libc/test/src/unistd/dup2_test.cpp b/libc/test/src/unistd/dup2_test.cpp
new file mode 100644
index 0000000000000..836c9abdc822b
--- /dev/null
+++ b/libc/test/src/unistd/dup2_test.cpp
@@ -0,0 +1,63 @@
+//===-- Unittests for dup -------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/fcntl/open.h"
+#include "src/unistd/close.h"
+#include "src/unistd/dup2.h"
+#include "src/unistd/read.h"
+#include "src/unistd/unlink.h"
+#include "src/unistd/write.h"
+#include "test/ErrnoSetterMatcher.h"
+#include "utils/UnitTest/Test.h"
+#include "utils/testutils/FDReader.h"
+
+#include <errno.h>
+
+TEST(LlvmLibcdupTest, ReadAndWriteViaDup) {
+ constexpr int DUPFD = 0xD0;
+ errno = 0;
+ using __llvm_libc::testing::ErrnoSetterMatcher::Succeeds;
+ constexpr const char *TEST_FILE = "testdata/dup.test";
+ int fd = __llvm_libc::open(TEST_FILE, O_WRONLY | O_CREAT, S_IRWXU);
+ ASSERT_EQ(errno, 0);
+ ASSERT_GT(fd, 0);
+ int dupfd = __llvm_libc::dup2(fd, DUPFD);
+ ASSERT_EQ(errno, 0);
+ ASSERT_EQ(dupfd, DUPFD);
+
+ // Write something via the dup
+ constexpr char WRITE_DATA[] = "Hello, dup!";
+ constexpr size_t WRITE_SIZE = sizeof(WRITE_DATA);
+ ASSERT_EQ(ssize_t(WRITE_SIZE),
+ __llvm_libc::write(dupfd, WRITE_DATA, WRITE_SIZE));
+ ASSERT_THAT(__llvm_libc::close(dupfd), Succeeds(0));
+
+ // Reopen the file for reading and create a dup.
+ fd = __llvm_libc::open(TEST_FILE, O_RDONLY);
+ ASSERT_EQ(errno, 0);
+ ASSERT_GT(fd, 0);
+ dupfd = __llvm_libc::dup2(fd, DUPFD);
+ ASSERT_EQ(errno, 0);
+ ASSERT_EQ(dupfd, DUPFD);
+
+ // Read the file content via the dup.
+ char buf[WRITE_SIZE];
+ ASSERT_THAT(__llvm_libc::read(dupfd, buf, WRITE_SIZE), Succeeds(WRITE_SIZE));
+ ASSERT_STREQ(buf, WRITE_DATA);
+
+ // Verify that duping to the same fd value succeeds.
+ ASSERT_THAT(__llvm_libc::dup2(dupfd, dupfd), Succeeds(dupfd));
+
+ ASSERT_THAT(__llvm_libc::close(dupfd), Succeeds(0));
+ ASSERT_THAT(__llvm_libc::unlink(TEST_FILE), Succeeds(0));
+}
+
+TEST(LlvmLibcdupTest, DupBadFD) {
+ using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+ ASSERT_THAT(__llvm_libc::dup2(-1, 123), Fails(EBADF));
+}
diff --git a/libc/test/src/unistd/dup3_test.cpp b/libc/test/src/unistd/dup3_test.cpp
new file mode 100644
index 0000000000000..e43b5ff43f095
--- /dev/null
+++ b/libc/test/src/unistd/dup3_test.cpp
@@ -0,0 +1,69 @@
+//===-- Unittests for dup3 ------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/fcntl/open.h"
+#include "src/unistd/close.h"
+#include "src/unistd/dup3.h"
+#include "src/unistd/read.h"
+#include "src/unistd/unlink.h"
+#include "src/unistd/write.h"
+#include "test/ErrnoSetterMatcher.h"
+#include "utils/UnitTest/Test.h"
+#include "utils/testutils/FDReader.h"
+
+#include <errno.h>
+
+// The tests here are exactly the same as those of dup2. We only test the
+// plumbing of the dup3 syscall and not the dup3 functionality itself as it is
+// a simple syscall wrapper. Testing dup3 functionality is beyond the scope of
+// this test.
+
+TEST(LlvmLibcdupTest, ReadAndWriteViaDup) {
+ constexpr int DUPFD = 0xD0;
+ errno = 0;
+ using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+ using __llvm_libc::testing::ErrnoSetterMatcher::Succeeds;
+ constexpr const char *TEST_FILE = "testdata/dup.test";
+ int fd = __llvm_libc::open(TEST_FILE, O_WRONLY | O_CREAT, S_IRWXU);
+ ASSERT_EQ(errno, 0);
+ ASSERT_GT(fd, 0);
+ int dupfd = __llvm_libc::dup3(fd, DUPFD, 0);
+ ASSERT_EQ(errno, 0);
+ ASSERT_EQ(dupfd, DUPFD);
+
+ // Write something via the dup
+ constexpr char WRITE_DATA[] = "Hello, dup!";
+ constexpr size_t WRITE_SIZE = sizeof(WRITE_DATA);
+ ASSERT_EQ(ssize_t(WRITE_SIZE),
+ __llvm_libc::write(dupfd, WRITE_DATA, WRITE_SIZE));
+ ASSERT_THAT(__llvm_libc::close(dupfd), Succeeds(0));
+
+ // Reopen the file for reading and create a dup.
+ fd = __llvm_libc::open(TEST_FILE, O_RDONLY);
+ ASSERT_EQ(errno, 0);
+ ASSERT_GT(fd, 0);
+ dupfd = __llvm_libc::dup3(fd, DUPFD, 0);
+ ASSERT_EQ(errno, 0);
+ ASSERT_EQ(dupfd, DUPFD);
+
+ // Read the file content via the dup.
+ char buf[WRITE_SIZE];
+ ASSERT_THAT(__llvm_libc::read(dupfd, buf, WRITE_SIZE), Succeeds(WRITE_SIZE));
+ ASSERT_STREQ(buf, WRITE_DATA);
+
+ // Verify that, unlike dup2, duping to the same fd value with dup3 fails.
+ ASSERT_THAT(__llvm_libc::dup3(dupfd, dupfd, 0), Fails(EINVAL));
+
+ ASSERT_THAT(__llvm_libc::close(dupfd), Succeeds(0));
+ ASSERT_THAT(__llvm_libc::unlink(TEST_FILE), Succeeds(0));
+}
+
+TEST(LlvmLibcdupTest, DupBadFD) {
+ using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+ ASSERT_THAT(__llvm_libc::dup3(-1, 123, 0), Fails(EBADF));
+}
diff --git a/libc/test/src/unistd/dup_test.cpp b/libc/test/src/unistd/dup_test.cpp
new file mode 100644
index 0000000000000..54f8b5d6c61c9
--- /dev/null
+++ b/libc/test/src/unistd/dup_test.cpp
@@ -0,0 +1,59 @@
+//===-- Unittests for dup -------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/fcntl/open.h"
+#include "src/unistd/close.h"
+#include "src/unistd/dup.h"
+#include "src/unistd/read.h"
+#include "src/unistd/unlink.h"
+#include "src/unistd/write.h"
+#include "test/ErrnoSetterMatcher.h"
+#include "utils/UnitTest/Test.h"
+#include "utils/testutils/FDReader.h"
+
+#include <errno.h>
+
+TEST(LlvmLibcdupTest, ReadAndWriteViaDup) {
+ errno = 0;
+ using __llvm_libc::testing::ErrnoSetterMatcher::Succeeds;
+ constexpr const char *TEST_FILE = "testdata/dup.test";
+ int fd = __llvm_libc::open(TEST_FILE, O_WRONLY | O_CREAT, S_IRWXU);
+ ASSERT_EQ(errno, 0);
+ ASSERT_GT(fd, 0);
+ int dupfd = __llvm_libc::dup(fd);
+ ASSERT_EQ(errno, 0);
+ ASSERT_GT(dupfd, 0);
+
+ // Write something via the dup
+ constexpr char WRITE_DATA[] = "Hello, dup!";
+ constexpr size_t WRITE_SIZE = sizeof(WRITE_DATA);
+ ASSERT_EQ(ssize_t(WRITE_SIZE),
+ __llvm_libc::write(dupfd, WRITE_DATA, WRITE_SIZE));
+ ASSERT_THAT(__llvm_libc::close(dupfd), Succeeds(0));
+
+ // Reopen the file for reading and create a dup.
+ fd = __llvm_libc::open(TEST_FILE, O_RDONLY);
+ ASSERT_EQ(errno, 0);
+ ASSERT_GT(fd, 0);
+ dupfd = __llvm_libc::dup(fd);
+ ASSERT_EQ(errno, 0);
+ ASSERT_GT(dupfd, 0);
+
+ // Read the file content via the dup.
+ char buf[WRITE_SIZE];
+ ASSERT_THAT(__llvm_libc::read(dupfd, buf, WRITE_SIZE), Succeeds(WRITE_SIZE));
+ ASSERT_STREQ(buf, WRITE_DATA);
+
+ ASSERT_THAT(__llvm_libc::close(dupfd), Succeeds(0));
+ ASSERT_THAT(__llvm_libc::unlink(TEST_FILE), Succeeds(0));
+}
+
+TEST(LlvmLibcdupTest, DupBadFD) {
+ using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+ ASSERT_THAT(__llvm_libc::dup(-1), Fails(EBADF));
+}
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