[libc-commits] [libc] [libc] Implement tcsetwinsize in termios (PR #228498)

Aman Maurya via libc-commits libc-commits at lists.llvm.org
Tue Oct 6 18:56:56 PDT 2026


https://github.com/amanmaurya92 updated https://github.com/llvm/llvm-project/pull/228498

>From 9d3245afed8a15301b4cf35e874aef40836e4b4c Mon Sep 17 00:00:00 2001
From: amanmaurya92 <amanmaurya9209 at gmail.com>
Date: Fri, 2 Oct 2026 21:27:37 +0530
Subject: [PATCH 1/3] [libc] Implement tcsetwinsize in termios

Implement the standard POSIX.1-2024 function tcsetwinsize in <termios.h>.

Fixes #228380
---
 libc/config/linux/aarch64/entrypoints.txt   |  1 +
 libc/config/linux/riscv/entrypoints.txt     |  1 +
 libc/config/linux/x86_64/entrypoints.txt    |  1 +
 libc/include/CMakeLists.txt                 |  1 +
 libc/include/termios.yaml                   |  9 +++
 libc/src/termios/CMakeLists.txt             |  8 +++
 libc/src/termios/linux/CMakeLists.txt       | 15 +++++
 libc/src/termios/linux/tcsetwinsize.cpp     | 38 +++++++++++
 libc/src/termios/tcsetwinsize.h             | 26 ++++++++
 libc/test/src/termios/CMakeLists.txt        | 19 ++++++
 libc/test/src/termios/tcsetwinsize_test.cpp | 71 +++++++++++++++++++++
 11 files changed, 190 insertions(+)
 create mode 100644 libc/src/termios/linux/tcsetwinsize.cpp
 create mode 100644 libc/src/termios/tcsetwinsize.h
 create mode 100644 libc/test/src/termios/tcsetwinsize_test.cpp

diff --git a/libc/config/linux/aarch64/entrypoints.txt b/libc/config/linux/aarch64/entrypoints.txt
index c7ded2fade05d9..f43e2b906fdfc0 100644
--- a/libc/config/linux/aarch64/entrypoints.txt
+++ b/libc/config/linux/aarch64/entrypoints.txt
@@ -437,6 +437,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.termios.tcgetsid
     libc.src.termios.tcsendbreak
     libc.src.termios.tcsetattr
+    libc.src.termios.tcsetwinsize
 
     # unistd.h entrypoints
     libc.src.unistd.alarm
diff --git a/libc/config/linux/riscv/entrypoints.txt b/libc/config/linux/riscv/entrypoints.txt
index 296985eeff937c..517da3cdab83a2 100644
--- a/libc/config/linux/riscv/entrypoints.txt
+++ b/libc/config/linux/riscv/entrypoints.txt
@@ -456,6 +456,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.termios.tcgetsid
     libc.src.termios.tcsendbreak
     libc.src.termios.tcsetattr
+    libc.src.termios.tcsetwinsize
 
     # unistd.h entrypoints
     libc.src.unistd.alarm
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 7928a35a6284a5..319a90216d93e4 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -476,6 +476,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.termios.tcgetsid
     libc.src.termios.tcsendbreak
     libc.src.termios.tcsetattr
+    libc.src.termios.tcsetwinsize
 
     # unistd.h entrypoints
     libc.src.unistd.alarm
diff --git a/libc/include/CMakeLists.txt b/libc/include/CMakeLists.txt
index 2fe1f92afc1d19..59deca11a9cdd2 100644
--- a/libc/include/CMakeLists.txt
+++ b/libc/include/CMakeLists.txt
@@ -1197,6 +1197,7 @@ add_header_macro(
     .llvm-libc-types.pid_t
     .llvm-libc-types.speed_t
     .llvm-libc-types.struct_termios
+    .llvm-libc-types.struct_winsize
     .llvm-libc-types.tcflag_t
 )
 
diff --git a/libc/include/termios.yaml b/libc/include/termios.yaml
index 21ee25d700d9ae..ef89c430253d5a 100644
--- a/libc/include/termios.yaml
+++ b/libc/include/termios.yaml
@@ -10,6 +10,7 @@ types:
   - type_name: speed_t
   - type_name: pid_t
   - type_name: cc_t
+  - type_name: struct_winsize
 enums: []
 objects: []
 functions:
@@ -87,3 +88,11 @@ functions:
       - type: int
       - type: int
       - type: struct termios *
+  - name: tcsetwinsize
+    standards:
+      - posix
+    return_type: int
+    arguments:
+      - type: int
+      - type: const struct winsize *
+
diff --git a/libc/src/termios/CMakeLists.txt b/libc/src/termios/CMakeLists.txt
index 0fbd632b78fbda..dd9516690e9862 100644
--- a/libc/src/termios/CMakeLists.txt
+++ b/libc/src/termios/CMakeLists.txt
@@ -78,3 +78,11 @@ add_entrypoint_object(
   DEPENDS
     .${LIBC_TARGET_OS}.tcsetattr
 )
+
+add_entrypoint_object(
+  tcsetwinsize
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.tcsetwinsize
+)
+
diff --git a/libc/src/termios/linux/CMakeLists.txt b/libc/src/termios/linux/CMakeLists.txt
index 86565cf1294c7d..1e18156c32784d 100644
--- a/libc/src/termios/linux/CMakeLists.txt
+++ b/libc/src/termios/linux/CMakeLists.txt
@@ -162,3 +162,18 @@ add_entrypoint_object(
     libc.src.errno.errno
     libc.src.__support.macros.null_check
 )
+
+add_entrypoint_object(
+  tcsetwinsize
+  SRCS
+    tcsetwinsize.cpp
+  HDRS
+    ../tcsetwinsize.h
+  DEPENDS
+    libc.hdr.types.struct_winsize
+    libc.src.__support.OSUtil.linux.syscall_wrappers.ioctl
+    libc.src.errno.errno
+    libc.src.__support.macros.config
+    libc.src.__support.macros.null_check
+)
+
diff --git a/libc/src/termios/linux/tcsetwinsize.cpp b/libc/src/termios/linux/tcsetwinsize.cpp
new file mode 100644
index 00000000000000..dfe28209e75276
--- /dev/null
+++ b/libc/src/termios/linux/tcsetwinsize.cpp
@@ -0,0 +1,38 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 tcsetwinsize.
+///
+//===----------------------------------------------------------------------===//
+
+#include "src/termios/tcsetwinsize.h"
+
+#include "hdr/types/struct_winsize.h"
+#include "src/__support/OSUtil/linux/syscall_wrappers/ioctl.h"
+#include "src/__support/common.h"
+#include "src/__support/libc_errno.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/null_check.h"
+
+#include <asm/ioctls.h> // Safe to include without the risk of name pollution.
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, tcsetwinsize, (int fd, const struct winsize *ws)) {
+  LIBC_CRASH_ON_NULLPTR(ws);
+
+  auto ret = linux_syscalls::ioctl(fd, TIOCSWINSZ, ws);
+  if (!ret.has_value()) {
+    libc_errno = ret.error();
+    return -1;
+  }
+  return 0;
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/termios/tcsetwinsize.h b/libc/src/termios/tcsetwinsize.h
new file mode 100644
index 00000000000000..48d5d300602877
--- /dev/null
+++ b/libc/src/termios/tcsetwinsize.h
@@ -0,0 +1,26 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+/// Header file for tcsetwinsize function.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_TERMIOS_TCSETWINSIZE_H
+#define LLVM_LIBC_SRC_TERMIOS_TCSETWINSIZE_H
+
+#include "hdr/types/struct_winsize.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int tcsetwinsize(int fd, const struct winsize *ws);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_TERMIOS_TCSETWINSIZE_H
diff --git a/libc/test/src/termios/CMakeLists.txt b/libc/test/src/termios/CMakeLists.txt
index a802b3e7aba2aa..2228af98780c33 100644
--- a/libc/test/src/termios/CMakeLists.txt
+++ b/libc/test/src/termios/CMakeLists.txt
@@ -23,3 +23,22 @@ add_libc_test(
     libc.test.UnitTest.ErrnoCheckingTest
     libc.test.UnitTest.ErrnoSetterMatcher
 )
+
+add_libc_test(
+  tcsetwinsize_test
+  SUITE
+    libc_termios_unittests
+  SRCS
+    tcsetwinsize_test.cpp
+  DEPENDS
+    libc.hdr.fcntl_macros
+    libc.hdr.types.struct_winsize
+    libc.src.errno.errno
+    libc.src.fcntl.open
+    libc.src.termios.tcsetwinsize
+    libc.src.unistd.close
+    libc.src.unistd.pipe
+    libc.test.UnitTest.ErrnoCheckingTest
+    libc.test.UnitTest.ErrnoSetterMatcher
+)
+
diff --git a/libc/test/src/termios/tcsetwinsize_test.cpp b/libc/test/src/termios/tcsetwinsize_test.cpp
new file mode 100644
index 00000000000000..4457a65dce89b4
--- /dev/null
+++ b/libc/test/src/termios/tcsetwinsize_test.cpp
@@ -0,0 +1,71 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+/// Unit tests for tcsetwinsize.
+///
+//===----------------------------------------------------------------------===//
+
+#include "hdr/fcntl_macros.h"
+#include "hdr/types/struct_winsize.h"
+#include "src/__support/libc_errno.h"
+#include "src/fcntl/open.h"
+#include "src/termios/tcsetwinsize.h"
+#include "src/unistd/close.h"
+#include "src/unistd/pipe.h"
+#include "test/UnitTest/ErrnoCheckingTest.h"
+#include "test/UnitTest/ErrnoSetterMatcher.h"
+#include "test/UnitTest/Test.h"
+
+using LlvmLibcTcSetWinSizeTest = LIBC_NAMESPACE::testing::ErrnoCheckingTest;
+using namespace LIBC_NAMESPACE::testing::ErrnoSetterMatcher;
+
+TEST_F(LlvmLibcTcSetWinSizeTest, InvalidFileDescriptor) {
+  constexpr unsigned short TEST_ROWS = 24;
+  constexpr unsigned short TEST_COLS = 80;
+  struct winsize ws = {TEST_ROWS, TEST_COLS, 0, 0};
+  ASSERT_THAT(LIBC_NAMESPACE::tcsetwinsize(-1, &ws), Fails(EBADF));
+}
+
+TEST_F(LlvmLibcTcSetWinSizeTest, NonTerminalFileDescriptor) {
+  int pipefd[2];
+  ASSERT_THAT(LIBC_NAMESPACE::pipe(pipefd), Succeeds(0));
+
+  constexpr unsigned short TEST_ROWS = 24;
+  constexpr unsigned short TEST_COLS = 80;
+  struct winsize ws = {TEST_ROWS, TEST_COLS, 0, 0};
+  ASSERT_THAT(LIBC_NAMESPACE::tcsetwinsize(pipefd[0], &ws), Fails(ENOTTY));
+  ASSERT_THAT(LIBC_NAMESPACE::tcsetwinsize(pipefd[1], &ws), Fails(ENOTTY));
+
+  ASSERT_THAT(LIBC_NAMESPACE::close(pipefd[0]), Succeeds(0));
+  ASSERT_THAT(LIBC_NAMESPACE::close(pipefd[1]), Succeeds(0));
+}
+
+TEST_F(LlvmLibcTcSetWinSizeTest, TerminalSmokeTest) {
+  int fd = LIBC_NAMESPACE::open("/dev/ptmx", O_RDWR);
+  if (fd < 0)
+    fd = LIBC_NAMESPACE::open("/dev/tty", O_RDWR);
+
+  if (fd < 0) {
+    // When no terminal is available, gracefully skip the test.
+    libc_errno = 0;
+    return;
+  }
+  ASSERT_ERRNO_SUCCESS();
+
+  constexpr unsigned short TEST_ROWS = 30;
+  constexpr unsigned short TEST_COLS = 100;
+  struct winsize ws = {TEST_ROWS, TEST_COLS, 0, 0};
+  int ret = LIBC_NAMESPACE::tcsetwinsize(fd, &ws);
+  if (ret < 0) {
+    ASSERT_ERRNO_EQ(ENOTTY);
+  } else {
+    ASSERT_ERRNO_SUCCESS();
+  }
+  ASSERT_THAT(LIBC_NAMESPACE::close(fd), Succeeds(0));
+}

>From f8ab73e19291d89b95bf448a3bb282f4e0ce1d1c Mon Sep 17 00:00:00 2001
From: amanmaurya92 <amanmaurya9209 at gmail.com>
Date: Tue, 6 Oct 2026 21:36:51 +0530
Subject: [PATCH 2/3] [libc] Address review feedback for tcsetwinsize

- Remove LIBC_CRASH_ON_NULLPTR and let kernel return EFAULT

- Use scope_exit to close file descriptors in unit tests

- Remove braces on single-statement if/else bodies

- Add NullPointer unit test checking for EFAULT
---
 libc/src/termios/linux/CMakeLists.txt       |  1 -
 libc/src/termios/linux/tcsetwinsize.cpp     |  3 --
 libc/test/src/termios/CMakeLists.txt        |  1 +
 libc/test/src/termios/tcsetwinsize_test.cpp | 31 +++++++++++++++++----
 4 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/libc/src/termios/linux/CMakeLists.txt b/libc/src/termios/linux/CMakeLists.txt
index 1e18156c32784d..2da7fcd861f47c 100644
--- a/libc/src/termios/linux/CMakeLists.txt
+++ b/libc/src/termios/linux/CMakeLists.txt
@@ -174,6 +174,5 @@ add_entrypoint_object(
     libc.src.__support.OSUtil.linux.syscall_wrappers.ioctl
     libc.src.errno.errno
     libc.src.__support.macros.config
-    libc.src.__support.macros.null_check
 )
 
diff --git a/libc/src/termios/linux/tcsetwinsize.cpp b/libc/src/termios/linux/tcsetwinsize.cpp
index dfe28209e75276..485fa0758f06ca 100644
--- a/libc/src/termios/linux/tcsetwinsize.cpp
+++ b/libc/src/termios/linux/tcsetwinsize.cpp
@@ -18,15 +18,12 @@
 #include "src/__support/common.h"
 #include "src/__support/libc_errno.h"
 #include "src/__support/macros/config.h"
-#include "src/__support/macros/null_check.h"
 
 #include <asm/ioctls.h> // Safe to include without the risk of name pollution.
 
 namespace LIBC_NAMESPACE_DECL {
 
 LLVM_LIBC_FUNCTION(int, tcsetwinsize, (int fd, const struct winsize *ws)) {
-  LIBC_CRASH_ON_NULLPTR(ws);
-
   auto ret = linux_syscalls::ioctl(fd, TIOCSWINSZ, ws);
   if (!ret.has_value()) {
     libc_errno = ret.error();
diff --git a/libc/test/src/termios/CMakeLists.txt b/libc/test/src/termios/CMakeLists.txt
index 2228af98780c33..4ef43f3a09c56a 100644
--- a/libc/test/src/termios/CMakeLists.txt
+++ b/libc/test/src/termios/CMakeLists.txt
@@ -33,6 +33,7 @@ add_libc_test(
   DEPENDS
     libc.hdr.fcntl_macros
     libc.hdr.types.struct_winsize
+    libc.src.__support.CPP.scope
     libc.src.errno.errno
     libc.src.fcntl.open
     libc.src.termios.tcsetwinsize
diff --git a/libc/test/src/termios/tcsetwinsize_test.cpp b/libc/test/src/termios/tcsetwinsize_test.cpp
index 4457a65dce89b4..add9d141b31212 100644
--- a/libc/test/src/termios/tcsetwinsize_test.cpp
+++ b/libc/test/src/termios/tcsetwinsize_test.cpp
@@ -13,6 +13,7 @@
 
 #include "hdr/fcntl_macros.h"
 #include "hdr/types/struct_winsize.h"
+#include "src/__support/CPP/scope.h"
 #include "src/__support/libc_errno.h"
 #include "src/fcntl/open.h"
 #include "src/termios/tcsetwinsize.h"
@@ -35,15 +36,16 @@ TEST_F(LlvmLibcTcSetWinSizeTest, InvalidFileDescriptor) {
 TEST_F(LlvmLibcTcSetWinSizeTest, NonTerminalFileDescriptor) {
   int pipefd[2];
   ASSERT_THAT(LIBC_NAMESPACE::pipe(pipefd), Succeeds(0));
+  LIBC_NAMESPACE::cpp::scope_exit close_pipe([&] {
+    ASSERT_THAT(LIBC_NAMESPACE::close(pipefd[0]), Succeeds(0));
+    ASSERT_THAT(LIBC_NAMESPACE::close(pipefd[1]), Succeeds(0));
+  });
 
   constexpr unsigned short TEST_ROWS = 24;
   constexpr unsigned short TEST_COLS = 80;
   struct winsize ws = {TEST_ROWS, TEST_COLS, 0, 0};
   ASSERT_THAT(LIBC_NAMESPACE::tcsetwinsize(pipefd[0], &ws), Fails(ENOTTY));
   ASSERT_THAT(LIBC_NAMESPACE::tcsetwinsize(pipefd[1], &ws), Fails(ENOTTY));
-
-  ASSERT_THAT(LIBC_NAMESPACE::close(pipefd[0]), Succeeds(0));
-  ASSERT_THAT(LIBC_NAMESPACE::close(pipefd[1]), Succeeds(0));
 }
 
 TEST_F(LlvmLibcTcSetWinSizeTest, TerminalSmokeTest) {
@@ -57,15 +59,32 @@ TEST_F(LlvmLibcTcSetWinSizeTest, TerminalSmokeTest) {
     return;
   }
   ASSERT_ERRNO_SUCCESS();
+  LIBC_NAMESPACE::cpp::scope_exit close_fd(
+      [&] { ASSERT_THAT(LIBC_NAMESPACE::close(fd), Succeeds(0)); });
 
   constexpr unsigned short TEST_ROWS = 30;
   constexpr unsigned short TEST_COLS = 100;
   struct winsize ws = {TEST_ROWS, TEST_COLS, 0, 0};
   int ret = LIBC_NAMESPACE::tcsetwinsize(fd, &ws);
-  if (ret < 0) {
+  if (ret < 0)
     ASSERT_ERRNO_EQ(ENOTTY);
-  } else {
+  else
     ASSERT_ERRNO_SUCCESS();
+}
+
+TEST_F(LlvmLibcTcSetWinSizeTest, NullPointer) {
+  int fd = LIBC_NAMESPACE::open("/dev/ptmx", O_RDWR);
+  if (fd < 0)
+    fd = LIBC_NAMESPACE::open("/dev/tty", O_RDWR);
+
+  if (fd < 0) {
+    // When no terminal is available, gracefully skip the test.
+    libc_errno = 0;
+    return;
   }
-  ASSERT_THAT(LIBC_NAMESPACE::close(fd), Succeeds(0));
+  ASSERT_ERRNO_SUCCESS();
+  LIBC_NAMESPACE::cpp::scope_exit close_fd(
+      [&] { ASSERT_THAT(LIBC_NAMESPACE::close(fd), Succeeds(0)); });
+
+  ASSERT_THAT(LIBC_NAMESPACE::tcsetwinsize(fd, nullptr), Fails(EFAULT));
 }

>From fb71dbcec5b87fb9f55be756f6590e423f7f9e2c Mon Sep 17 00:00:00 2001
From: amanmaurya92 <amanmaurya9209 at gmail.com>
Date: Wed, 7 Oct 2026 07:00:06 +0530
Subject: [PATCH 3/3] [libc] Use proxy header for ioctl macros and avoid
 /dev/tty in tcsetwinsize test

- Include hdr/sys_ioctl_macros.h instead of asm/ioctls.h

- Restrict tests to /dev/ptmx to avoid resizing user's terminal window
---
 libc/src/termios/linux/CMakeLists.txt       |  1 +
 libc/src/termios/linux/tcsetwinsize.cpp     |  3 +--
 libc/test/src/termios/tcsetwinsize_test.cpp | 21 +++++++++++++--------
 3 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/libc/src/termios/linux/CMakeLists.txt b/libc/src/termios/linux/CMakeLists.txt
index 2da7fcd861f47c..93133b5a79b45b 100644
--- a/libc/src/termios/linux/CMakeLists.txt
+++ b/libc/src/termios/linux/CMakeLists.txt
@@ -170,6 +170,7 @@ add_entrypoint_object(
   HDRS
     ../tcsetwinsize.h
   DEPENDS
+    libc.hdr.sys_ioctl_macros
     libc.hdr.types.struct_winsize
     libc.src.__support.OSUtil.linux.syscall_wrappers.ioctl
     libc.src.errno.errno
diff --git a/libc/src/termios/linux/tcsetwinsize.cpp b/libc/src/termios/linux/tcsetwinsize.cpp
index 485fa0758f06ca..0fe5af12464ca4 100644
--- a/libc/src/termios/linux/tcsetwinsize.cpp
+++ b/libc/src/termios/linux/tcsetwinsize.cpp
@@ -13,14 +13,13 @@
 
 #include "src/termios/tcsetwinsize.h"
 
+#include "hdr/sys_ioctl_macros.h"
 #include "hdr/types/struct_winsize.h"
 #include "src/__support/OSUtil/linux/syscall_wrappers/ioctl.h"
 #include "src/__support/common.h"
 #include "src/__support/libc_errno.h"
 #include "src/__support/macros/config.h"
 
-#include <asm/ioctls.h> // Safe to include without the risk of name pollution.
-
 namespace LIBC_NAMESPACE_DECL {
 
 LLVM_LIBC_FUNCTION(int, tcsetwinsize, (int fd, const struct winsize *ws)) {
diff --git a/libc/test/src/termios/tcsetwinsize_test.cpp b/libc/test/src/termios/tcsetwinsize_test.cpp
index add9d141b31212..cdcdfbca6f19fe 100644
--- a/libc/test/src/termios/tcsetwinsize_test.cpp
+++ b/libc/test/src/termios/tcsetwinsize_test.cpp
@@ -49,12 +49,11 @@ TEST_F(LlvmLibcTcSetWinSizeTest, NonTerminalFileDescriptor) {
 }
 
 TEST_F(LlvmLibcTcSetWinSizeTest, TerminalSmokeTest) {
+  // Use a pseudo-terminal master rather than /dev/tty so running tests in an
+  // interactive terminal does not resize the user's window.
   int fd = LIBC_NAMESPACE::open("/dev/ptmx", O_RDWR);
-  if (fd < 0)
-    fd = LIBC_NAMESPACE::open("/dev/tty", O_RDWR);
-
   if (fd < 0) {
-    // When no terminal is available, gracefully skip the test.
+    // When /dev/ptmx is not available, gracefully skip the test.
     libc_errno = 0;
     return;
   }
@@ -74,11 +73,8 @@ TEST_F(LlvmLibcTcSetWinSizeTest, TerminalSmokeTest) {
 
 TEST_F(LlvmLibcTcSetWinSizeTest, NullPointer) {
   int fd = LIBC_NAMESPACE::open("/dev/ptmx", O_RDWR);
-  if (fd < 0)
-    fd = LIBC_NAMESPACE::open("/dev/tty", O_RDWR);
-
   if (fd < 0) {
-    // When no terminal is available, gracefully skip the test.
+    // When /dev/ptmx is not available, gracefully skip the test.
     libc_errno = 0;
     return;
   }
@@ -86,5 +82,14 @@ TEST_F(LlvmLibcTcSetWinSizeTest, NullPointer) {
   LIBC_NAMESPACE::cpp::scope_exit close_fd(
       [&] { ASSERT_THAT(LIBC_NAMESPACE::close(fd), Succeeds(0)); });
 
+  constexpr unsigned short TEST_ROWS = 24;
+  constexpr unsigned short TEST_COLS = 80;
+  struct winsize ws = {TEST_ROWS, TEST_COLS, 0, 0};
+  int ret = LIBC_NAMESPACE::tcsetwinsize(fd, &ws);
+  if (ret < 0) {
+    ASSERT_ERRNO_EQ(ENOTTY);
+    return;
+  }
+
   ASSERT_THAT(LIBC_NAMESPACE::tcsetwinsize(fd, nullptr), Fails(EFAULT));
 }



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