parisc: Fix stack unwinder

Debugging shows a large number of unaligned access traps in the unwinder
code. Code analysis reveals a number of issues with this code:

- handle_interruption is passed twice through
  dereference_kernel_function_descriptor()
- ret_from_kernel_thread, syscall_exit, intr_return,
  _switch_to_ret, and _call_on_stack are passed through
  dereference_kernel_function_descriptor() even though they are
  not declared as function pointers.

To fix the problems, drop one of the calls to
dereference_kernel_function_descriptor() for handle_interruption,
and compare the other pointers directly.

Fixes: 6414b30 ("parisc: unwind: Avoid missing prototype warning for handle_interruption()")
Fixes: 8e0ba12 ("parisc/unwind: fix unwinder when CONFIG_64BIT is enabled")
Cc: Helge Deller <deller@gmx.de>
Cc: Sven Schnelle <svens@stackframe.org>
Cc: John David Anglin <dave.anglin@bell.net>
Cc: Charlie Jenkins <charlie@rivosinc.com>
Cc: David Laight <David.Laight@ACULAB.COM>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Helge Deller <deller@gmx.de>

Author: groeck

arch/parisc/kernel/unwind.c

@@ -228,24 +228,22 @@ static int unwind_special(struct unwind_frame_info *info, unsigned long pc, int
 #ifdef CONFIG_IRQSTACKS
 	extern void * const _call_on_stack;
 #endif /* CONFIG_IRQSTACKS */
-	void *ptr;
 
-	ptr = dereference_kernel_function_descriptor(&handle_interruption);
-	if (pc_is_kernel_fn(pc, ptr)) {
+	if (pc_is_kernel_fn(pc, handle_interruption)) {
 		struct pt_regs *regs = (struct pt_regs *)(info->sp - frame_size - PT_SZ_ALGN);
 		dbg("Unwinding through handle_interruption()\n");
 		info->prev_sp = regs->gr[30];
 		info->prev_ip = regs->iaoq[0];
 		return 1;
 	}
 
-	if (pc_is_kernel_fn(pc, ret_from_kernel_thread) ||
-	    pc_is_kernel_fn(pc, syscall_exit)) {
+	if (pc == (unsigned long)&ret_from_kernel_thread ||
+	    pc == (unsigned long)&syscall_exit) {
 		info->prev_sp = info->prev_ip = 0;
 		return 1;
 	}
 
-	if (pc_is_kernel_fn(pc, intr_return)) {
+	if (pc == (unsigned long)&intr_return) {
 		struct pt_regs *regs;
 
 		dbg("Found intr_return()\n");
@@ -257,14 +255,14 @@ static int unwind_special(struct unwind_frame_info *info, unsigned long pc, int
 	}
 
 	if (pc_is_kernel_fn(pc, _switch_to) ||
-	    pc_is_kernel_fn(pc, _switch_to_ret)) {
+	    pc == (unsigned long)&_switch_to_ret) {
 		info->prev_sp = info->sp - CALLEE_SAVE_FRAME_SIZE;
 		info->prev_ip = *(unsigned long *)(info->prev_sp - RP_OFFSET);
 		return 1;
 	}
 
 #ifdef CONFIG_IRQSTACKS
-	if (pc_is_kernel_fn(pc, _call_on_stack)) {
+	if (pc == (unsigned long)&_call_on_stack) {
 		info->prev_sp = *(unsigned long *)(info->sp - FRAME_SIZE - REG_SZ);
 		info->prev_ip = *(unsigned long *)(info->sp - FRAME_SIZE - RP_OFFSET);
 		return 1;