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)

2 files changed, 11 insertions, 1 deletions

diff --git a/Python/dup2.c b/Python/dup2.c
index 7c6bbfc..a1df049 100644
--- a/Python/dup2.c
+++ b/Python/dup2.c
@@ -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;
 }
diff --git a/Python/fileutils.c b/Python/fileutils.c
index 7e5d01f..fb1e5ef 100644
--- a/Python/fileutils.c
+++ b/Python/fileutils.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;
 }