powerpc: Enable compile-time check for syscall handlers

The table of syscall handlers and registered compatibility syscall
handlers has in past been produced using assembly, with function
references resolved at link time. This moves link-time errors to
compile-time, by rewriting systbl.S in C, and including the
linux/syscalls.h, linux/compat.h and asm/syscalls.h headers for
prototypes.

Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220921065605.1051927-18-rmclure@linux.ibm.com

Author: rohanmclure

arch/powerpc/kernel/systbl.S renamed to arch/powerpc/kernel/systbl.c

@@ -10,36 +10,26 @@
  * PPC64 updates by Dave Engebretsen (engebret@us.ibm.com) 
  */
 
-#include <asm/ppc_asm.h>
+#include <linux/syscalls.h>
+#include <linux/compat.h>
+#include <asm/unistd.h>
+#include <asm/syscalls.h>
 
-#ifdef CONFIG_RELOCATABLE
-.section .data.rel.ro,"aw"
-#else
-.section .rodata,"a"
-#endif
+#define __SYSCALL_WITH_COMPAT(nr, entry, compat) __SYSCALL(nr, entry)
+#define __SYSCALL(nr, entry) [nr] = (unsigned long) &entry,
 
-#ifdef CONFIG_PPC64
-	.p2align	3
-#define __SYSCALL(nr, entry)	.8byte entry
-#else
-	.p2align	2
-#define __SYSCALL(nr, entry)	.long entry
-#endif
-
-#define __SYSCALL_WITH_COMPAT(nr, native, compat)	__SYSCALL(nr, native)
-.globl sys_call_table
-sys_call_table:
+const unsigned long sys_call_table[] = {
 #ifdef CONFIG_PPC64
 #include <asm/syscall_table_64.h>
 #else
 #include <asm/syscall_table_32.h>
 #endif
+};
 
 #ifdef CONFIG_COMPAT
 #undef __SYSCALL_WITH_COMPAT
 #define __SYSCALL_WITH_COMPAT(nr, native, compat)	__SYSCALL(nr, compat)
-.globl compat_sys_call_table
-compat_sys_call_table:
-#define compat_sys_sigsuspend	sys_sigsuspend
+const unsigned long compat_sys_call_table[] = {
 #include <asm/syscall_table_32.h>
-#endif
+};
+#endif /* CONFIG_COMPAT */