powerpc: Fix BUG_ON() reporting in real mode

I ran into this issue while debugging an early boot problem. The system
hit a BUG_ON() but report bug failed to print the line number and file
name. The reason being that the system was running in real mode and
report_bug() searches for addresses in the PAGE_OFFSET+ region.

Suggested-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Balbir Singh <bsingharora@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index b6becc7..4e5c11d 100644 (file)
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -1148,6 +1148,7 @@ void __kprobes program_check_exception(struct pt_regs *regs)
                goto bail;
        }
        if (reason & REASON_TRAP) {
+               unsigned long bugaddr;
                /* Debugger is first in line to stop recursive faults in
                 * rcu_lock, notify_die, or atomic_notifier_call_chain */
                if (debugger_bpt(regs))
@@ -1158,8 +1159,15 @@ void __kprobes program_check_exception(struct pt_regs *regs)
                                == NOTIFY_STOP)
                        goto bail;
 
+               bugaddr = regs->nip;
+               /*
+                * Fixup bugaddr for BUG_ON() in real mode
+                */
+               if (!is_kernel_addr(bugaddr) && !(regs->msr & MSR_IR))
+                       bugaddr += PAGE_OFFSET;
+
                if (!(regs->msr & MSR_PR) &&  /* not user-mode */
-                   report_bug(regs->nip, regs) == BUG_TRAP_TYPE_WARN) {
+                   report_bug(bugaddr, regs) == BUG_TRAP_TYPE_WARN) {
                        regs->nip += 4;
                        goto bail;
                }