gh-153400: Use pidfd_open() and pidfd_getfd() functions

Use pidfd_open() and pidfd_getfd() functions if available (glibc 2.36
and newer), instead of using syscall().

Author: vstinner

Misc/NEWS.d/next/Library/2026-08-10-22-11-15.gh-issue-153400.Ds3GI3.rst

@@ -0,0 +1,3 @@
+:mod:`os`: Use ``pidfd_open()`` and ``pidfd_getfd()`` functions if available
+(glibc 2.36 and newer), instead of using ``syscall()``. Patch by Victor
+Stinner.

Modules/posixmodule.c

@@ -10810,8 +10810,9 @@ os_wait_impl(PyObject *module)
 
 
 // This system call always crashes on older Android versions.
-#if defined(__linux__) && defined(__NR_pidfd_open) && \
-    !(defined(__ANDROID__) && __ANDROID_API__ < 31)
+#if defined(HAVE_PIDFD_OPEN) \
+    || (defined(__linux__) && defined(__NR_pidfd_open) \
+        && !(defined(__ANDROID__) && __ANDROID_API__ < 31))
 /*[clinic input]
 os.pidfd_open
   pid: pid_t
@@ -10827,7 +10828,11 @@ static PyObject *
 os_pidfd_open_impl(PyObject *module, pid_t pid, unsigned int flags)
 /*[clinic end generated code: output=5c7252698947dc41 input=03058b32c389f874]*/
 {
+#ifdef HAVE_PIDFD_OPEN
+    int fd = pidfd_open(pid, flags);
+#else
     int fd = syscall(__NR_pidfd_open, pid, flags);
+#endif
     if (fd < 0) {
         return posix_error();
     }
@@ -10836,8 +10841,9 @@ os_pidfd_open_impl(PyObject *module, pid_t pid, unsigned int flags)
 #endif
 
 
-#if defined(__linux__) && defined(__NR_pidfd_getfd) && \
-    !(defined(__ANDROID__) && __ANDROID_API__ < 31)
+#if defined(HAVE_PIDFD_GETFD) \
+    || (defined(__linux__) && defined(__NR_pidfd_getfd) \
+        && !(defined(__ANDROID__) && __ANDROID_API__ < 31))
 /*[clinic input]
 os.pidfd_getfd
   pidfd: int
@@ -10856,7 +10862,11 @@ os_pidfd_getfd_impl(PyObject *module, int pidfd, int targetfd,
                     unsigned int flags)
 /*[clinic end generated code: output=e1a1415a13c7137f input=ef6417fb10deb1cc]*/
 {
+#ifdef HAVE_PIDFD_GETFD
+    int fd = pidfd_getfd(pidfd, targetfd, flags);
+#else
     int fd = syscall(__NR_pidfd_getfd, pidfd, targetfd, flags);
+#endif
     if (fd < 0) {
         return posix_error();
     }

configure

@@ -5503,7 +5503,8 @@ AC_CHECK_FUNCS([ \
   getpwent getpwnam_r getpwuid getpwuid_r getresgid getresuid getrusage getsid getspent \
   getspnam getuid getwd grantpt if_nameindex initgroups kill killpg lchown linkat \
   lockf lstat lutimes madvise mbrtowc memrchr mkdirat mkfifo mkfifoat \
-  mknod mknodat mktime mmap mremap nice openat opendir pathconf pause pipe \
+  mknod mknodat mktime mmap mremap nice openat opendir pathconf pause \
+  pidfd_open pidfd_getfd pipe \
   plock poll ppoll posix_fadvise posix_fallocate posix_openpt posix_spawn posix_spawnp \
   posix_spawn_file_actions_addclosefrom_np \
   pread preadv preadv2 process_vm_readv \

configure.ac

@@ -1046,6 +1046,12 @@
 /* Define to 1 if you have the 'pause' function. */
 #undef HAVE_PAUSE
 
+/* Define to 1 if you have the 'pidfd_getfd' function. */
+#undef HAVE_PIDFD_GETFD
+
+/* Define to 1 if you have the 'pidfd_open' function. */
+#undef HAVE_PIDFD_OPEN
+
 /* Define to 1 if you have the 'pipe' function. */
 #undef HAVE_PIPE