2 files changed, 14 insertions, 2 deletions

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 8a13d468635a..50e0d2bc4528 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -176,7 +176,7 @@
 /*
  * This is a sneaky trick to help the unwinder find pt_regs on the stack.  The
  * frame pointer is replaced with an encoded pointer to pt_regs.  The encoding
- * is just setting the LSB, which makes it an invalid stack address and is also
+ * is just clearing the MSB, which makes it an invalid stack address and is also
  * a signal to the unwinder that it's a pt_regs pointer in disguise.
  *
  * NOTE: This macro must be used *after* SAVE_ALL because it corrupts the
@@ -185,7 +185,7 @@
 .macro ENCODE_FRAME_POINTER
 #ifdef CONFIG_FRAME_POINTER
         mov %esp, %ebp
-        orl $0x1, %ebp
+        andl $0x7fffffff, %ebp
 #endif
 .endm
 
diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
index d05637726c10..4949bbc95f75 100644
--- a/arch/x86/kernel/unwind_frame.c
+++ b/arch/x86/kernel/unwind_frame.c
@@ -174,6 +174,7 @@ static bool is_last_task_frame(struct unwind_state *state)
  * This determines if the frame pointer actually contains an encoded pointer to
  * pt_regs on the stack.  See ENCODE_FRAME_POINTER.
  */
+#ifdef CONFIG_X86_64
 static struct pt_regs *decode_frame_pointer(unsigned long *bp)
 {
         unsigned long regs = (unsigned long)bp;
@@ -183,6 +184,17 @@ static struct pt_regs *decode_frame_pointer(unsigned long *bp)
 
         return (struct pt_regs *)(regs & ~0x1);
 }
+#else
+static struct pt_regs *decode_frame_pointer(unsigned long *bp)
+{
+        unsigned long regs = (unsigned long)bp;
+
+        if (regs & 0x80000000)
+                return NULL;
+
+        return (struct pt_regs *)(regs | 0x80000000);
+}
+#endif
 
 #ifdef CONFIG_X86_32
 #define KERNEL_REGS_SIZE (sizeof(struct pt_regs) - 2*sizeof(long))