[PATCH v2] Fix for "bt" command prints a bogus warning

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Currently, the "bt" command may print a bogus exception frame
and the remaining frame will be truncated on x86 64 when using the
"virsh send-key <kvm guest> KEY_LEFTALT KEY_SYSRQ KEY_C" command
to trigger a panic from the KVM host. For example:

  crash> bt
  PID: 0        TASK: ffff9e7a47e32f00  CPU: 3    COMMAND: "swapper/3"
   #0 [ffffba7900118bb8] machine_kexec at ffffffff87e5c2c7
   #1 [ffffba7900118c08] __crash_kexec at ffffffff87f9500d
   #2 [ffffba7900118cd0] panic at ffffffff87edfff9
   #3 [ffffba7900118d50] sysrq_handle_crash at ffffffff883ce2c1
   #4 [ffffba7900118d58] __handle_sysrq.cold.15 at ffffffff883ceb56
   #5 [ffffba7900118d88] sysrq_filter at ffffffff883ce9a2
   #6 [ffffba7900118dc0] input_to_handler at ffffffff884fb0bf
   #7 [ffffba7900118df8] input_pass_values at ffffffff884fc1b7
   #8 [ffffba7900118e20] input_handle_event at ffffffff884fe278
   #9 [ffffba7900118e50] input_event at ffffffff884fe74b
   #10 [ffffba7900118e88] atkbd_interrupt at ffffffff88504e2f
   #11 [ffffba7900118ee0] serio_interrupt at ffffffff884f7516
   #12 [ffffba7900118f10] i8042_interrupt at ffffffff884f8b04
   #13 [ffffba7900118f50] __handle_irq_event_percpu at ffffffff87f51430
   #14 [ffffba7900118f90] handle_irq_event_percpu at ffffffff87f51590
   #15 [ffffba7900118fb8] handle_irq_event at ffffffff87f51616
   #16 [ffffba7900118fd8] handle_edge_irq at ffffffff87f559f2
   #17 [ffffba7900118ff0] asm_call_on_stack at ffffffff88800fa2
   --- <IRQ stack> ---
   #18 [ffffba790008bda0] asm_call_on_stack at ffffffff88800fa2
       RIP: ffffffffffffffff  RSP: 0000000000000124  RFLAGS: 00000003
       RAX: 0000000000000000  RBX: 0000000000000001  RCX: 0000000000000000
       RDX: ffffffff88800c1e  RSI: 0000000000000000  RDI: 0000000000000000
       RBP: 0000000000000001   R8: 0000000000000000   R9: 0000000000000000
       R10: 0000000000000000  R11: ffffffff88760555  R12: ffffba790008be08
       R13: ffffffff87f18002  R14: ffff9e7a47e32f00  R15: ffff9e7bb6198e00
       ORIG_RAX: 0000000000000000  CS: 0003  SS: 0000
  bt: WARNING: possibly bogus exception frame
  crash>

The following related kernel commits cause the current issue, crash
needs to adjust the value of irq eframe.

Related kernel commits:
[1] v5.8: 931b94145981 ("x86/entry: Provide helpers for executing on the irqstack")
[2] v5.8: fa5e5c409213 ("x86/entry: Use idtentry for interrupts")
[3] v5.12: 52d743f3b712 ("x86/softirq: Remove indirection in do_softirq_own_stack()")

Signed-off-by: Lianbo Jiang <lijiang@xxxxxxxxxx>
Signed-off-by: Kazuhito Hagio <k-hagio-ab@xxxxxxx>
---
 x86_64.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/x86_64.c b/x86_64.c
index 7a5d6f050c89..5b671bd97775 100644
--- a/x86_64.c
+++ b/x86_64.c
@@ -3938,6 +3938,11 @@ in_exception_stack:
         if (irq_eframe) {
                 bt->flags |= BT_EXCEPTION_FRAME;
                 i = (irq_eframe - bt->stackbase)/sizeof(ulong);
+                if (symbol_exists("asm_common_interrupt")) {
+			i -= 1;
+			up = (ulong *)(&bt->stackbuf[i*sizeof(ulong)]);
+			bt->instptr = *up;
+                }
                 x86_64_print_stack_entry(bt, ofp, level, i, bt->instptr);
                 bt->flags &= ~(ulonglong)BT_EXCEPTION_FRAME;
                 cs = x86_64_exception_frame(EFRAME_PRINT|EFRAME_CS, 0, 
@@ -6521,6 +6526,14 @@ x86_64_irq_eframe_link_init(void)
 	else
 		return; 
 
+	if (symbol_exists("asm_common_interrupt")) {
+		if (symbol_exists("asm_call_on_stack"))
+			machdep->machspec->irq_eframe_link = -64;
+		else
+			machdep->machspec->irq_eframe_link = -32;
+		return;
+	}
+
 	if (THIS_KERNEL_VERSION < LINUX(2,6,9)) 
 		return;
 
-- 
2.37.1

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