powerpc: Use common syscall handler type

Cause syscall handlers to be typed as follows when called indirectly
throughout the kernel. This is to allow for better type checking.

typedef long (*syscall_fn)(unsigned long, unsigned long, unsigned long,
                           unsigned long, unsigned long, unsigned long);

Since both 32 and 64-bit abis allow for at least the first six
machine-word length parameters to a function to be passed by registers,
even handlers which admit fewer than six parameters may be viewed as
having the above type.

Coercing syscalls to syscall_fn requires a cast to void* to avoid
-Wcast-function-type.

Fixup comparisons in VDSO to avoid pointer-integer comparison. Introduce
explicit cast on systems with SPUs.

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/20220921065605.1051927-19-rmclure@linux.ibm.com

Author: rohanmclure

arch/powerpc/include/asm/syscall.h

@@ -14,9 +14,12 @@
 #include <linux/sched.h>
 #include <linux/thread_info.h>
 
+typedef long (*syscall_fn)(unsigned long, unsigned long, unsigned long,
+			   unsigned long, unsigned long, unsigned long);
+
 /* ftrace syscalls requires exporting the sys_call_table */
-extern const unsigned long sys_call_table[];
-extern const unsigned long compat_sys_call_table[];
+extern const syscall_fn sys_call_table[];
+extern const syscall_fn compat_sys_call_table[];
 
 static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 {

arch/powerpc/include/asm/syscalls.h

@@ -8,6 +8,7 @@
 #include <linux/types.h>
 #include <linux/compat.h>
 
+#include <asm/syscall.h>
 #ifdef CONFIG_PPC64
 #include <asm/syscalls_32.h>
 #endif

arch/powerpc/kernel/syscall.c

@@ -12,8 +12,6 @@
 #include <asm/unistd.h>
 
 
-typedef long (*syscall_fn)(long, long, long, long, long, long);
-
 /* Has to run notrace because it is entered not completely "reconciled" */
 notrace long system_call_exception(long r3, long r4, long r5,
 				   long r6, long r7, long r8,

arch/powerpc/kernel/systbl.c

@@ -16,9 +16,14 @@
 #include <asm/syscalls.h>
 
 #define __SYSCALL_WITH_COMPAT(nr, entry, compat) __SYSCALL(nr, entry)
-#define __SYSCALL(nr, entry) [nr] = (unsigned long) &entry,
 
-const unsigned long sys_call_table[] = {
+/*
+ * Coerce syscall handlers with arbitrary parameters to common type
+ * requires cast to void* to avoid -Wcast-function-type.
+ */
+#define __SYSCALL(nr, entry) [nr] = (void *) entry,
+
+const syscall_fn sys_call_table[] = {
 #ifdef CONFIG_PPC64
 #include <asm/syscall_table_64.h>
 #else
@@ -29,7 +34,7 @@ const unsigned long sys_call_table[] = {
 #ifdef CONFIG_COMPAT
 #undef __SYSCALL_WITH_COMPAT
 #define __SYSCALL_WITH_COMPAT(nr, native, compat)	__SYSCALL(nr, compat)
-const unsigned long compat_sys_call_table[] = {
+const syscall_fn compat_sys_call_table[] = {
 #include <asm/syscall_table_32.h>
 };
 #endif /* CONFIG_COMPAT */

arch/powerpc/kernel/vdso.c

@@ -304,10 +304,10 @@ static void __init vdso_setup_syscall_map(void)
 	unsigned int i;
 
 	for (i = 0; i < NR_syscalls; i++) {
-		if (sys_call_table[i] != (unsigned long)&sys_ni_syscall)
+		if (sys_call_table[i] != (void *)&sys_ni_syscall)
 			vdso_data->syscall_map[i >> 5] |= 0x80000000UL >> (i & 0x1f);
 		if (IS_ENABLED(CONFIG_COMPAT) &&
-		    compat_sys_call_table[i] != (unsigned long)&sys_ni_syscall)
+		    compat_sys_call_table[i] != (void *)&sys_ni_syscall)
 			vdso_data->compat_syscall_map[i >> 5] |= 0x80000000UL >> (i & 0x1f);
 	}
 }

arch/powerpc/platforms/cell/spu_callbacks.c

@@ -34,15 +34,15 @@
  *	mbind, mq_open, ipc, ...
  */
 
-static void *spu_syscall_table[] = {
+static const syscall_fn spu_syscall_table[] = {
 #define __SYSCALL_WITH_COMPAT(nr, entry, compat) __SYSCALL(nr, entry)
-#define __SYSCALL(nr, entry) [nr] = entry,
+#define __SYSCALL(nr, entry) [nr] = (void *) entry,
 #include <asm/syscall_table_spu.h>
 };
 
 long spu_sys_callback(struct spu_syscall_block *s)
 {
-	long (*syscall)(u64 a1, u64 a2, u64 a3, u64 a4, u64 a5, u64 a6);
+	syscall_fn syscall;
 
 	if (s->nr_ret >= ARRAY_SIZE(spu_syscall_table)) {
 		pr_debug("%s: invalid syscall #%lld", __func__, s->nr_ret);