Prefer SYS_getrandom with __NR_getrandom fallback

Use the libc-provided SYS_getrandom syscall number when available,
falling back to the kernel-provided __NR_getrandom when necessary.

Author: jjhelmus

Modules/posixmodule.c

@@ -160,6 +160,9 @@
 #ifdef HAVE_SYS_SYSCALL_H
 #  include <sys/syscall.h>        // syscall(), __NR_xxx syscall numbers
 #endif
+#if !defined(SYS_getrandom) && defined(__NR_getrandom)
+#  define SYS_getrandom __NR_getrandom
+#endif
 
 #ifdef HAVE_POSIX_SPAWN
 #  include <spawn.h>              // posix_spawn()
@@ -17440,7 +17443,7 @@ os_getrandom_impl(PyObject *module, Py_ssize_t size, unsigned int flags)
 #ifdef HAVE_GETRANDOM
         n = getrandom(data, size, flags);
 #else
-        n = syscall(__NR_getrandom, data, size, flags);
+        n = syscall(SYS_getrandom, data, size, flags);
 #endif
         if (n < 0 && errno == EINTR) {
             if (PyErr_CheckSignals() < 0) {

Python/bootstrap_hash.c

@@ -23,7 +23,10 @@
 #    include <sys/random.h>       // getrandom()
 #  endif
 #  if !defined(HAVE_GETRANDOM) && defined(HAVE_GETRANDOM_SYSCALL)
-#    include <sys/syscall.h>      // __NR_getrandom
+#    include <sys/syscall.h>      // __NR_getrandom, SYS_getrandom
+#    if !defined(SYS_getrandom) && defined(__NR_getrandom)
+#      define SYS_getrandom __NR_getrandom
+#    endif
 #  endif
 #endif
 
@@ -128,11 +131,11 @@ py_getrandom(void *buffer, Py_ssize_t size, int blocking, int raise)
 #else
         if (raise) {
             Py_BEGIN_ALLOW_THREADS
-            n = syscall(__NR_getrandom, dest, n, flags);
+            n = syscall(SYS_getrandom, dest, n, flags);
             Py_END_ALLOW_THREADS
         }
         else {
-            n = syscall(__NR_getrandom, dest, n, flags);
+            n = syscall(SYS_getrandom, dest, n, flags);
         }
 #  ifdef _Py_MEMORY_SANITIZER
         if (n > 0) {

configure

@@ -7807,12 +7807,16 @@ AC_LINK_IFELSE(
     #include <sys/syscall.h>
     #include <linux/random.h>
 
+    #if !defined(SYS_getrandom) && defined(__NR_getrandom)
+    #  define SYS_getrandom __NR_getrandom
+    #endif
+
     int main(void) {
         char buffer[1];
         const size_t buflen = sizeof(buffer);
         const int flags = GRND_NONBLOCK;
         /* ignore the result, Python checks for ENOSYS and EAGAIN at runtime */
-        (void)syscall(__NR_getrandom, buffer, buflen, flags);
+        (void)syscall(SYS_getrandom, buffer, buflen, flags);
         return 0;
     }
   ]])