[libc-commits] [libc] [libc] Add support for SYS_fchmodat2 in fchmodat (PR #223997)
Aman Maurya via libc-commits
libc-commits at lists.llvm.org
Thu Sep 17 01:06:58 PDT 2026
https://github.com/amanmaurya92 updated https://github.com/llvm/llvm-project/pull/223997
>From 175097f9f5f61db71a7993221d93dbf35257dfec Mon Sep 17 00:00:00 2001
From: amanmaurya92 <amanmaurya9209 at gmail.com>
Date: Wed, 16 Sep 2026 18:11:59 +0530
Subject: [PATCH 1/5] [libc] Add support for SYS_fchmodat2 in fchmodat
Diagnosed using Antigravity.
Fixes #223953
---
.../linux/syscall_wrappers/CMakeLists.txt | 5 ++-
.../OSUtil/linux/syscall_wrappers/fchmodat.h | 19 +++++++-
libc/src/sys/stat/linux/CMakeLists.txt | 1 -
libc/src/sys/stat/linux/fchmodat.cpp | 7 +--
libc/test/src/sys/stat/fchmodat_test.cpp | 45 ++++++++++++++++---
5 files changed, 60 insertions(+), 17 deletions(-)
diff --git a/libc/src/__support/OSUtil/linux/syscall_wrappers/CMakeLists.txt b/libc/src/__support/OSUtil/linux/syscall_wrappers/CMakeLists.txt
index 17665f87dfcd84..8455b5f4050064 100644
--- a/libc/src/__support/OSUtil/linux/syscall_wrappers/CMakeLists.txt
+++ b/libc/src/__support/OSUtil/linux/syscall_wrappers/CMakeLists.txt
@@ -649,12 +649,13 @@ add_header_library(
HDRS
fchmodat.h
DEPENDS
+ libc.hdr.errno_macros
+ libc.hdr.types.mode_t
+ libc.include.sys_syscall
libc.src.__support.OSUtil.osutil
libc.src.__support.common
libc.src.__support.error_or
libc.src.__support.macros.config
- libc.hdr.types.mode_t
- libc.include.sys_syscall
)
add_header_library(
diff --git a/libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h b/libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h
index b62a040e9fe54f..558f097687a272 100644
--- a/libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h
+++ b/libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h
@@ -14,6 +14,7 @@
#ifndef LLVM_LIBC_SRC___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_FCHMODAT_H
#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_FCHMODAT_H
+#include "hdr/errno_macros.h"
#include "hdr/types/mode_t.h"
#include "src/__support/OSUtil/linux/syscall.h" // syscall_impl
#include "src/__support/common.h"
@@ -24,8 +25,24 @@
namespace LIBC_NAMESPACE_DECL {
namespace linux_syscalls {
-LIBC_INLINE ErrorOr<int> fchmodat(int fd, const char *path, mode_t mode) {
+LIBC_INLINE ErrorOr<int> fchmodat(int fd, const char *path, mode_t mode,
+ int flags) {
+#ifdef SYS_fchmodat2
+ int ret = syscall_impl<int>(SYS_fchmodat2, fd, path, mode, flags);
+#if defined(SYS_fchmodat)
+ if (ret == -ENOSYS) {
+ if (flags != 0)
+ return Error(ENOTSUP);
+ ret = syscall_impl<int>(SYS_fchmodat, fd, path, mode);
+ }
+#endif
+#elif defined(SYS_fchmodat)
+ if (flags != 0)
+ return Error(ENOTSUP);
int ret = syscall_impl<int>(SYS_fchmodat, fd, path, mode);
+#else
+#error "fchmodat2 and fchmodat syscalls not available."
+#endif
if (ret < 0)
return Error(-ret);
return ret;
diff --git a/libc/src/sys/stat/linux/CMakeLists.txt b/libc/src/sys/stat/linux/CMakeLists.txt
index b35cd11ea8da52..b087fc927459c7 100644
--- a/libc/src/sys/stat/linux/CMakeLists.txt
+++ b/libc/src/sys/stat/linux/CMakeLists.txt
@@ -30,7 +30,6 @@ add_entrypoint_object(
HDRS
../fchmodat.h
DEPENDS
- libc.hdr.errno_macros
libc.hdr.types.mode_t
libc.src.__support.OSUtil.linux.syscall_wrappers.fchmodat
libc.src.errno.errno
diff --git a/libc/src/sys/stat/linux/fchmodat.cpp b/libc/src/sys/stat/linux/fchmodat.cpp
index 29bee319ed0add..38e02b5d616176 100644
--- a/libc/src/sys/stat/linux/fchmodat.cpp
+++ b/libc/src/sys/stat/linux/fchmodat.cpp
@@ -8,7 +8,6 @@
#include "src/sys/stat/fchmodat.h"
-#include "hdr/errno_macros.h"
#include "src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h"
#include "src/__support/common.h"
#include "src/__support/libc_errno.h"
@@ -18,11 +17,7 @@ namespace LIBC_NAMESPACE_DECL {
LLVM_LIBC_FUNCTION(int, fchmodat,
(int dirfd, const char *path, mode_t mode, int flags)) {
- if (flags != 0) {
- libc_errno = ENOTSUP;
- return -1;
- }
- auto result = linux_syscalls::fchmodat(dirfd, path, mode);
+ auto result = linux_syscalls::fchmodat(dirfd, path, mode, flags);
if (!result) {
libc_errno = result.error();
return -1;
diff --git a/libc/test/src/sys/stat/fchmodat_test.cpp b/libc/test/src/sys/stat/fchmodat_test.cpp
index 868cdb2bc817ac..f068ce131c6cd7 100644
--- a/libc/test/src/sys/stat/fchmodat_test.cpp
+++ b/libc/test/src/sys/stat/fchmodat_test.cpp
@@ -67,11 +67,42 @@ TEST_F(LlvmLibcFchmodatTest, NonExistentFile) {
Fails(ENOENT));
}
-TEST_F(LlvmLibcFchmodatTest, UnsupportedFlags) {
- ASSERT_THAT(LIBC_NAMESPACE::fchmodat(AT_FDCWD, "non-existent-file", S_IRUSR,
- AT_SYMLINK_NOFOLLOW),
- Fails(ENOTSUP));
- ASSERT_THAT(
- LIBC_NAMESPACE::fchmodat(AT_FDCWD, "non-existent-file", S_IRUSR, -1),
- Fails(ENOTSUP));
+TEST_F(LlvmLibcFchmodatTest, Flags) {
+ constexpr const char *TEST_FILE = "testdata/fchmodat_flags.test";
+ int fd = LIBC_NAMESPACE::open(TEST_FILE, O_CREAT | O_WRONLY, S_IRWXU);
+ ASSERT_GT(fd, 0);
+ ASSERT_ERRNO_SUCCESS();
+ ASSERT_THAT(LIBC_NAMESPACE::close(fd), Succeeds(0));
+
+ int ret = LIBC_NAMESPACE::fchmodat(AT_FDCWD, TEST_FILE, S_IRUSR,
+ AT_SYMLINK_NOFOLLOW);
+ if (ret == 0) {
+ // SYS_fchmodat2 is supported by the kernel.
+ ASSERT_ERRNO_SUCCESS();
+ ASSERT_THAT(LIBC_NAMESPACE::fchmodat(AT_FDCWD, "non-existent-file", S_IRUSR,
+ AT_SYMLINK_NOFOLLOW),
+ Fails(ENOENT));
+ // Test AT_EMPTY_PATH on an open file descriptor.
+ fd = LIBC_NAMESPACE::open(TEST_FILE, O_PATH);
+ ASSERT_GT(fd, 0);
+ ASSERT_ERRNO_SUCCESS();
+ EXPECT_THAT(LIBC_NAMESPACE::fchmodat(fd, "", S_IRWXU, AT_EMPTY_PATH),
+ Succeeds(0));
+ ASSERT_THAT(LIBC_NAMESPACE::close(fd), Succeeds(0));
+
+ ASSERT_THAT(LIBC_NAMESPACE::fchmodat(AT_FDCWD, TEST_FILE, S_IRUSR, -1),
+ Fails(EINVAL));
+ } else {
+ // Kernel or compile-time headers do not support fchmodat2; non-zero flags
+ // fail with ENOTSUP.
+ ASSERT_ERRNO_EQ(ENOTSUP);
+ ASSERT_THAT(LIBC_NAMESPACE::fchmodat(AT_FDCWD, "non-existent-file", S_IRUSR,
+ AT_SYMLINK_NOFOLLOW),
+ Fails(ENOTSUP));
+ ASSERT_THAT(
+ LIBC_NAMESPACE::fchmodat(AT_FDCWD, TEST_FILE, S_IRUSR, AT_EMPTY_PATH),
+ Fails(ENOTSUP));
+ ASSERT_THAT(LIBC_NAMESPACE::fchmodat(AT_FDCWD, TEST_FILE, S_IRUSR, -1),
+ Fails(ENOTSUP));
+ }
}
>From 106383244f747fbdb9b9cd48d17dd54cd01d0471 Mon Sep 17 00:00:00 2001
From: Aman Maurya <amanmaurya9209 at gmail.com>
Date: Wed, 16 Sep 2026 20:40:43 +0530
Subject: [PATCH 2/5] Update
libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h
Co-authored-by: Pavel Labath <pavel at labath.sk>
---
libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h b/libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h
index 558f097687a272..603aed5487e97c 100644
--- a/libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h
+++ b/libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h
@@ -27,7 +27,7 @@ namespace linux_syscalls {
LIBC_INLINE ErrorOr<int> fchmodat(int fd, const char *path, mode_t mode,
int flags) {
-#ifdef SYS_fchmodat2
+#if defined(SYS_fchmodat2)
int ret = syscall_impl<int>(SYS_fchmodat2, fd, path, mode, flags);
#if defined(SYS_fchmodat)
if (ret == -ENOSYS) {
>From c789df27bce19b084a6de5a632479eb983708f41 Mon Sep 17 00:00:00 2001
From: amanmaurya92 <amanmaurya9209 at gmail.com>
Date: Wed, 16 Sep 2026 20:53:32 +0530
Subject: [PATCH 3/5] [libc] Use syscall_checked in fchmodat and drop runtime
ENOSYS fallback
---
.../OSUtil/linux/syscall_wrappers/fchmodat.h | 16 +++-------------
1 file changed, 3 insertions(+), 13 deletions(-)
diff --git a/libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h b/libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h
index 603aed5487e97c..daeb4c1391b178 100644
--- a/libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h
+++ b/libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h
@@ -16,7 +16,7 @@
#include "hdr/errno_macros.h"
#include "hdr/types/mode_t.h"
-#include "src/__support/OSUtil/linux/syscall.h" // syscall_impl
+#include "src/__support/OSUtil/linux/syscall.h" // syscall_checked
#include "src/__support/common.h"
#include "src/__support/error_or.h"
#include "src/__support/macros/config.h"
@@ -28,24 +28,14 @@ namespace linux_syscalls {
LIBC_INLINE ErrorOr<int> fchmodat(int fd, const char *path, mode_t mode,
int flags) {
#if defined(SYS_fchmodat2)
- int ret = syscall_impl<int>(SYS_fchmodat2, fd, path, mode, flags);
-#if defined(SYS_fchmodat)
- if (ret == -ENOSYS) {
- if (flags != 0)
- return Error(ENOTSUP);
- ret = syscall_impl<int>(SYS_fchmodat, fd, path, mode);
- }
-#endif
+ return syscall_checked<int>(SYS_fchmodat2, fd, path, mode, flags);
#elif defined(SYS_fchmodat)
if (flags != 0)
return Error(ENOTSUP);
- int ret = syscall_impl<int>(SYS_fchmodat, fd, path, mode);
+ return syscall_checked<int>(SYS_fchmodat, fd, path, mode);
#else
#error "fchmodat2 and fchmodat syscalls not available."
#endif
- if (ret < 0)
- return Error(-ret);
- return ret;
}
} // namespace linux_syscalls
>From c9b5287d4fae9f0d52076e1f42b7a508e42bd631 Mon Sep 17 00:00:00 2001
From: amanmaurya92 <amanmaurya9209 at gmail.com>
Date: Wed, 16 Sep 2026 22:39:41 +0530
Subject: [PATCH 4/5] [libc] Restore runtime ENOSYS fallback for SYS_fchmodat2
---
.../__support/OSUtil/linux/syscall_wrappers/fchmodat.h | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h b/libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h
index daeb4c1391b178..2af227895d1f0a 100644
--- a/libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h
+++ b/libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h
@@ -28,7 +28,15 @@ namespace linux_syscalls {
LIBC_INLINE ErrorOr<int> fchmodat(int fd, const char *path, mode_t mode,
int flags) {
#if defined(SYS_fchmodat2)
- return syscall_checked<int>(SYS_fchmodat2, fd, path, mode, flags);
+ auto ret = syscall_checked<int>(SYS_fchmodat2, fd, path, mode, flags);
+#if defined(SYS_fchmodat)
+ if (!ret && ret.error() == ENOSYS) {
+ if (flags != 0)
+ return Error(ENOTSUP);
+ return syscall_checked<int>(SYS_fchmodat, fd, path, mode);
+ }
+#endif
+ return ret;
#elif defined(SYS_fchmodat)
if (flags != 0)
return Error(ENOTSUP);
>From 8956af172670ef3e425cf4232c77762c03292d9d Mon Sep 17 00:00:00 2001
From: Aman Maurya <amanmaurya9209 at gmail.com>
Date: Thu, 17 Sep 2026 13:36:45 +0530
Subject: [PATCH 5/5] Update
libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h
Co-authored-by: Pavel Labath <pavel at labath.sk>
---
.../OSUtil/linux/syscall_wrappers/fchmodat.h | 13 ++-----------
1 file changed, 2 insertions(+), 11 deletions(-)
diff --git a/libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h b/libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h
index 2af227895d1f0a..d294b9c36bdb0a 100644
--- a/libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h
+++ b/libc/src/__support/OSUtil/linux/syscall_wrappers/fchmodat.h
@@ -29,21 +29,12 @@ LIBC_INLINE ErrorOr<int> fchmodat(int fd, const char *path, mode_t mode,
int flags) {
#if defined(SYS_fchmodat2)
auto ret = syscall_checked<int>(SYS_fchmodat2, fd, path, mode, flags);
-#if defined(SYS_fchmodat)
- if (!ret && ret.error() == ENOSYS) {
- if (flags != 0)
- return Error(ENOTSUP);
- return syscall_checked<int>(SYS_fchmodat, fd, path, mode);
- }
+ if (ret || ret.error() != ENOSYS)
+ return ret;
#endif
- return ret;
-#elif defined(SYS_fchmodat)
if (flags != 0)
return Error(ENOTSUP);
return syscall_checked<int>(SYS_fchmodat, fd, path, mode);
-#else
-#error "fchmodat2 and fchmodat syscalls not available."
-#endif
}
} // namespace linux_syscalls
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