x86: set bp field in pt_regs properly

Save rbp twice: One is for marking the stack frame, as usual (already
there), and the other, to fill pt_regs properly. This is because bx
comes right before the last saved register in that structure, and not
bp. If the base pointer were in the place bx is today, this would not
be needed.

Signed-off-by: Glauber Costa <gcosta@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 7 insertions, 0 deletions

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index cf3a0b2d0059..25bb3f9b2552 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -667,6 +667,13 @@ END(stub_rt_sigreturn)
         SAVE_ARGS
         leaq -ARGOFFSET(%rsp),%rdi      # arg1 for handler
         pushq %rbp
+        /*
+         * Save rbp twice: One is for marking the stack frame, as usual, and the
+         * other, to fill pt_regs properly. This is because bx comes right
+         * before the last saved register in that structure, and not bp. If the
+         * base pointer were in the place bx is today, this would not be needed.
+         */
+        movq %rbp, -8(%rsp)
         CFI_ADJUST_CFA_OFFSET   8
         CFI_REL_OFFSET          rbp, 0
         movq %rsp,%rbp