gh-95174: Handle missing dup() and constants in WASI (GH-95229)

- check for ``dup()`` libc function
- handle missing ``F_DUPFD`` in ``dup2()`` replacement function
- add workaround for WASI libc bug in MSG_TRUNC
- ESHUTDOWN is missing, use EPIPE instead
- POLLPRI is missing, define as 0 (no-op)

Author: tiran

Misc/NEWS.d/next/Build/2022-07-25-08-59-35.gh-issue-95174.g8woUW.rst

@@ -0,0 +1,2 @@
+Python now detects missing ``dup`` function in WASI and works around some
+missing :mod:`errno`, :mod:`select`, and :mod:`socket` constants.

Modules/clinic/posixmodule.c.h

@@ -280,6 +280,10 @@ errno_exec(PyObject *module)
 #ifdef ENOANO
     add_errcode("ENOANO", ENOANO, "No anode");
 #endif
+#if defined(__wasi__) && !defined(ESHUTDOWN)
+    // WASI SDK 16 does not have ESHUTDOWN, shutdown results in EPIPE.
+    #define ESHUTDOWN EPIPE
+#endif
 #ifdef ESHUTDOWN
     add_errcode("ESHUTDOWN", ESHUTDOWN, "Cannot send after transport endpoint shutdown");
 #else

Modules/errnomodule.c

@@ -9316,7 +9316,9 @@ os_dup_impl(PyObject *module, int fd)
     return _Py_dup(fd);
 }
 
-
+// dup2() is either provided by libc or dup2.c with AC_REPLACE_FUNCS().
+// dup2.c provides working dup2() if and only if F_DUPFD is available.
+#if (defined(HAVE_DUP3) || defined(F_DUPFD) || defined(MS_WINDOWS))
 /*[clinic input]
 os.dup2 -> int
     fd: int
@@ -9416,6 +9418,7 @@ os_dup2_impl(PyObject *module, int fd, int fd2, int inheritable)
 
     return res;
 }
+#endif
 
 
 #ifdef HAVE_LOCKF

Modules/posixmodule.c

@@ -63,6 +63,11 @@ extern void bzero(void *, int);
 #  define SOCKET int
 #endif
 
+// WASI SDK 16 does not have POLLPRIO, define as no-op
+#if defined(__wasi__) && !defined(POLLPRI)
+#  define POLLPRI 0
+#endif
+
 typedef struct {
     PyObject *close;
     PyTypeObject *poll_Type;

Modules/selectmodule.c

@@ -7786,6 +7786,10 @@ PyInit__socket(void)
     PyModule_AddIntMacro(m, MSG_EOR);
 #endif
 #ifdef  MSG_TRUNC
+    // workaround for https://github.com/WebAssembly/wasi-libc/issues/305
+    #if defined(__wasi__) && !defined(__WASI_RIFLAGS_RECV_DATA_TRUNCATED)
+    #  define __WASI_RIFLAGS_RECV_DATA_TRUNCATED 2
+    #endif
     PyModule_AddIntMacro(m, MSG_TRUNC);
 #endif
 #ifdef  MSG_CTRUNC

Modules/socketmodule.c

@@ -678,6 +678,9 @@ Py_NO_ENABLE_SHARED to find out.  Also support MS_NO_COREDLL for b/w compat */
 /* Define if you have the 'inet_pton' function. */
 #define HAVE_INET_PTON 1
 
+/* Define to 1 if you have the `dup' function. */
+#define HAVE_DUP 1
+
 /* framework name */
 #define _PYTHONFRAMEWORK ""
 

PC/pyconfig.h

@@ -11,6 +11,7 @@
  * Return fd2 if all went well; return BADEXIT otherwise.
  */
 
+#include <errno.h>
 #include <fcntl.h>
 #include <unistd.h>
 
@@ -20,12 +21,17 @@ int
 dup2(int fd1, int fd2)
 {
     if (fd1 != fd2) {
+#ifdef F_DUPFD
         if (fcntl(fd1, F_GETFL) < 0)
             return BADEXIT;
         if (fcntl(fd2, F_GETFL) >= 0)
             close(fd2);
         if (fcntl(fd1, F_DUPFD, fd2) < 0)
             return BADEXIT;
+#else
+        errno = ENOTSUP;
+        return BADEXIT;
+#endif
     }
     return fd2;
 }

Python/dup2.c

@@ -2366,7 +2366,7 @@ _Py_dup(int fd)
         return -1;
     }
 
-#else
+#elif HAVE_DUP
     Py_BEGIN_ALLOW_THREADS
     _Py_BEGIN_SUPPRESS_IPH
     fd = dup(fd);
@@ -2383,6 +2383,10 @@ _Py_dup(int fd)
         _Py_END_SUPPRESS_IPH
         return -1;
     }
+#else
+    errno = ENOTSUP;
+    PyErr_SetFromErrno(PyExc_OSError);
+    return -1;
 #endif
     return fd;
 }