Improve system call wrappers

This change improves copy_file_range(), sendfile(), splice(), openpty(),
closefrom(), close_range(), fadvise() and posix_fadvise() in addition to
writing tests that confirm things like errno and seeking behavior across
platforms. We now less aggressively polyfill behavior with some of these
functions when the platform support isn't available. Please see:

https://justine.lol/cosmopolitan/functions.html

libc/calls/splice.c

@@ -17,58 +17,80 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/calls.h"
-#include "libc/calls/internal.h"
 #include "libc/calls/syscall-sysv.internal.h"
 #include "libc/dce.h"
 #include "libc/errno.h"
+#include "libc/fmt/itoa.h"
+#include "libc/intrin/asan.internal.h"
+#include "libc/intrin/describeflags.internal.h"
+#include "libc/intrin/strace.internal.h"
+#include "libc/mem/alloca.h"
+#include "libc/str/str.h"
 #include "libc/sysv/errfuns.h"
+#include "libc/thread/thread.h"
 
-static ssize_t splicer(int infd, int64_t *inoffset, int outfd,
-                       int64_t *outoffset, size_t uptobytes, uint32_t flags,
-                       int64_t impl(int infd, int64_t *inoffset, int outfd,
-                                    int64_t *outoffset, size_t uptobytes,
-                                    uint32_t flags)) {
-  int olderr;
-  ssize_t transferred;
-  if (!uptobytes || flags == -1) return einval();
-  if (IsModeDbg() && uptobytes > 1) uptobytes >>= 1;
-  olderr = errno;
-  if (__isfdkind(infd, kFdZip) || __isfdkind(outfd, kFdZip) ||
-      (transferred =
-           impl(infd, inoffset, outfd, outoffset, uptobytes, flags)) == -1 &&
-          errno == ENOSYS) {
-    errno = olderr;
-    transferred = copyfd(infd, inoffset, outfd, outoffset, uptobytes, flags);
+static struct Splice {
+  pthread_once_t once;
+  bool ok;
+} g_splice;
+
+static bool HasSplice(void) {
+  bool ok;
+  int e, rc;
+  e = errno;
+  if (IsLinux()) {
+    // Our testing indicates splice() doesn't work as documneted on
+    // RHEL5 and RHEL7 so let's require a modern kernel to be safe.
+    // We choose close_range() for this since it's listed by pledge
+    ok = sys_close_range(-1, -2, 0) == -1 && errno == EINVAL;
+  } else {
+    ok = false;
   }
-  return transferred;
+  errno = e;
+  return ok;
+}
+
+static void splice_init(void) {
+  g_splice.ok = HasSplice();
 }
 
 /**
  * Transfers data to/from pipe.
  *
  * @param flags can have SPLICE_F_{MOVE,NONBLOCK,MORE,GIFT}
+ * @param opt_in_out_inoffset may be specified if `infd` isn't a pipe and is
+ *     used as both an input and output parameter for pread() behavior
+ * @param opt_in_out_outoffset may be specified if `outfd` isn't a pipe and is
+ *     used as both an input and output parameter for pwrite() behavior
  * @return number of bytes transferred, 0 on input end, or -1 w/ errno
+ * @raise EBADF if `infd` or `outfd` aren't open files or append-only
+ * @raise ESPIPE if an offset arg was specified for a pipe fd
+ * @raise EINVAL if offset was given for non-seekable device
+ * @raise EINVAL if file system doesn't support splice()
+ * @raise EFAULT if one of the pointers memory is bad
+ * @raise EINVAL if `flags` is invalid
+ * @raise ENOSYS if not Linux 5.9+
  * @see copy_file_range() for file ↔ file
  * @see sendfile() for seekable → socket
  */
-ssize_t splice(int infd, int64_t *inopt_out_inoffset, int outfd,
-               int64_t *inopt_out_outoffset, size_t uptobytes, uint32_t flags) {
-  return splicer(infd, inopt_out_inoffset, outfd, inopt_out_outoffset,
-                 uptobytes, flags, sys_splice);
-}
-
-/**
- * Transfers data between files.
- *
- * @param outfd should be a writable file, but not O_APPEND
- * @param flags is reserved for future use
- * @return number of bytes actually copied, or -1 w/ errno
- * @see sendfile() for seekable → socket
- * @see splice() for fd ↔ pipe
- */
-ssize_t copy_file_range(int infd, int64_t *inopt_out_inoffset, int outfd,
-                        int64_t *inopt_out_outoffset, size_t uptobytes,
-                        uint32_t flags) {
-  return splicer(infd, inopt_out_inoffset, outfd, inopt_out_outoffset,
-                 uptobytes, flags, sys_copy_file_range);
+ssize_t splice(int infd, int64_t *opt_in_out_inoffset, int outfd,
+               int64_t *opt_in_out_outoffset, size_t uptobytes,
+               uint32_t flags) {
+  ssize_t rc;
+  pthread_once(&g_splice.once, splice_init);
+  if (!g_splice.ok) {
+    rc = enosys();
+  } else if (IsAsan() && ((opt_in_out_inoffset &&
+                           !__asan_is_valid(opt_in_out_inoffset, 8)) ||
+                          (opt_in_out_outoffset &&
+                           !__asan_is_valid(opt_in_out_outoffset, 8)))) {
+    rc = efault();
+  } else {
+    rc = sys_splice(infd, opt_in_out_inoffset, outfd, opt_in_out_outoffset,
+                    uptobytes, flags);
+  }
+  STRACE("splice(%d, %s, %d, %s, %'zu, %#x) → %'ld% m", infd,
+         DescribeInOutInt64(rc, opt_in_out_inoffset), outfd,
+         DescribeInOutInt64(rc, opt_in_out_outoffset), uptobytes, flags);
+  return rc;
 }