workaround broken msghdr struct on 64bit linux

POSIX clearly specifies the type of msg_iovlen and msg_controllen, and
Linux ignores it and makes them both size_t instead. to work around
this we add padding (instead of just using the wrong types like glibc
does), but we also need to patch-up the struct before passing it to
the kernel in case the caller did not zero-fill it.

if i could trust the kernel to just ignore the upper 32 bits, this
would not be necessary, but i don't think it will ignore them...

arch/x86_64/bits/socket.h

@@ -3,9 +3,9 @@ struct msghdr
 	void *msg_name;
 	socklen_t msg_namelen;
 	struct iovec *msg_iov;
-	int msg_iovlen;
+	int msg_iovlen, __pad1;
 	void *msg_control;
-	socklen_t msg_controllen;
+	socklen_t msg_controllen, __pad2;
 	int msg_flags;
 };
 

src/network/recvmsg.c

@@ -1,12 +1,24 @@
 #include <sys/socket.h>
+#include <limits.h>
 #include "syscall.h"
 #include "libc.h"
 
 ssize_t recvmsg(int fd, struct msghdr *msg, int flags)
 {
 	ssize_t r;
+#if LONG_MAX > INT_MAX
+	struct msghdr h, *orig = msg;
+	if (msg) {
+		h = *msg;
+		h.__pad1 = h.__pad2 = 0;
+		msg = &h;
+	}
+#endif
 	CANCELPT_BEGIN;
 	r = socketcall(recvmsg, fd, msg, flags, 0, 0, 0);
 	CANCELPT_END;
+#if LONG_MAX > INT_MAX
+	if (orig) *orig = h;
+#endif
 	return r;
 }

src/network/sendmsg.c

@@ -1,10 +1,19 @@
 #include <sys/socket.h>
+#include <limits.h>
 #include "syscall.h"
 #include "libc.h"
 
 ssize_t sendmsg(int fd, const struct msghdr *msg, int flags)
 {
 	ssize_t r;
+#if LONG_MAX > INT_MAX
+	struct msghdr h;
+	if (msg) {
+		h = *msg;
+		h.__pad1 = h.__pad2 = 0;
+		msg = &h;
+	}
+#endif
 	CANCELPT_BEGIN;
 	r = socketcall(sendmsg, fd, msg, flags, 0, 0, 0);
 	CANCELPT_END;