parisc/unwind: fix unwinder when CONFIG_64BIT is enabled

With 64 bit kernels unwind_special() is not working because
it compares the pc to the address of the function descriptor.
Add a helper function that compares pc with the dereferenced
address. This fixes all of the backtraces on my c8000. Without
this changes, a lot of backtraces are missing in kdb or the
show-all-tasks command from /proc/sysrq-trigger.
Signed-off-by: Sven Schnelle <svens@stackframe.org>
Signed-off-by: Helge Deller <deller@gmx.de>

arch/parisc/kernel/unwind.c

@@ -21,6 +21,8 @@
 #include <asm/ptrace.h>
 
 #include <asm/unwind.h>
+#include <asm/switch_to.h>
+#include <asm/sections.h>
 
 /* #define DEBUG 1 */
 #ifdef DEBUG
@@ -203,6 +205,11 @@ int __init unwind_init(void)
 	return 0;
 }
 
+static bool pc_is_kernel_fn(unsigned long pc, void *fn)
+{
+	return (unsigned long)dereference_kernel_function_descriptor(fn) == pc;
+}
+
 static int unwind_special(struct unwind_frame_info *info, unsigned long pc, int frame_size)
 {
 	/*
@@ -221,7 +228,7 @@ static int unwind_special(struct unwind_frame_info *info, unsigned long pc, int
 	extern void * const _call_on_stack;
 #endif /* CONFIG_IRQSTACKS */
 
-	if (pc == (unsigned long) &handle_interruption) {
+	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];
@@ -229,13 +236,13 @@ static int unwind_special(struct unwind_frame_info *info, unsigned long pc, int
 		return 1;
 	}
 
-	if (pc == (unsigned long) &ret_from_kernel_thread ||
-	    pc == (unsigned long) &syscall_exit) {
+	if (pc_is_kernel_fn(pc, ret_from_kernel_thread) ||
+	    pc_is_kernel_fn(pc, syscall_exit)) {
 		info->prev_sp = info->prev_ip = 0;
 		return 1;
 	}
 
-	if (pc == (unsigned long) &intr_return) {
+	if (pc_is_kernel_fn(pc, intr_return)) {
 		struct pt_regs *regs;
 
 		dbg("Found intr_return()\n");
@@ -246,20 +253,20 @@ static int unwind_special(struct unwind_frame_info *info, unsigned long pc, int
 		return 1;
 	}
 
-	if (pc == (unsigned long) &_switch_to_ret) {
+	if (pc_is_kernel_fn(pc, _switch_to) ||
+	    pc_is_kernel_fn(pc, _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 == (unsigned long) &_call_on_stack) {
+	if (pc_is_kernel_fn(pc, _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;
 	}
 #endif
-
 	return 0;
 }