x86/syscalls: Disallow compat entries for all types of 64-bit syscalls

A "compat" entry in the syscall tables means to use a different entry on
32-bit and 64-bit builds.

This only makes sense for syscalls that exist in the first place in 32-bit
builds, so disallow it for anything other than i386.

Signed-off-by: Andy Lutomirski <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Link: https://lkml.kernel.org/r/4b7565954c5a06530ac01d98cb1592538fd8ae51.1562185330.git.luto@kernel.org

Author: amluto

arch/x86/entry/syscalls/syscalltbl.sh

@@ -27,8 +27,8 @@ emit() {
     compat="$4"
     umlentry=""
 
-    if [ "$abi" = "64" -a -n "$compat" ]; then
-	echo "a compat entry for a 64-bit syscall makes no sense" >&2
+    if [ "$abi" != "I386" -a -n "$compat" ]; then
+	echo "a compat entry ($abi: $compat) for a 64-bit syscall makes no sense" >&2
 	exit 1
     fi