x86: push old stack address on irqstack for unwinder

Impact: Fixes dumpstack and KDB on 64 bits

This re-adds the old stack pointer to the top of the irqstack to help
with unwinding.  It was removed in commit d99015b1abbad743aa049b439c1e1dede6d0fa49
as part of the save_args out-of-line work.

Both dumpstack and KDB require this information.

Signed-off-by: Martin Hicks <mort@sgi.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index e28c7a987793..a1346217e43c 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -346,6 +346,7 @@ ENTRY(save_args)
         popq_cfi %rax                   /* move return address... */
         mov %gs:pda_irqstackptr,%rsp
         EMPTY_FRAME 0
+        pushq_cfi %rbp                  /* backlink for unwinder */
         pushq_cfi %rax                  /* ... to the new stack */
         /*
          * We entered an interrupt context - irqs are off: