x86: move stack_canary into irq_stack

Impact: x86_64 percpu area layout change, irq_stack now at the beginning

Now that the PDA is empty except for the stack canary, it can be removed.
The irqstack is moved to the start of the per-cpu section.  If the stack
protector is enabled, the canary overlaps the bottom 48 bytes of the irqstack.

tj: * updated subject
    * dropped asm relocation of irq_stack_ptr
    * updated comments a bit
    * rebased on top of stack canary changes

Signed-off-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/arch/x86/kernel/vmlinux_64.lds.S b/arch/x86/kernel/vmlinux_64.lds.S
index a09abb8fb97f..c9740996430a 100644
--- a/arch/x86/kernel/vmlinux_64.lds.S
+++ b/arch/x86/kernel/vmlinux_64.lds.S
@@ -220,8 +220,7 @@ SECTIONS
    * so that it can be accessed as a percpu variable.
    */
   . = ALIGN(PAGE_SIZE);
-  PERCPU_VADDR_PREALLOC(0, :percpu, pda_size)
-  per_cpu____pda = __per_cpu_start;
+  PERCPU_VADDR(0, :percpu)
 #else
   PERCPU(PAGE_SIZE)
 #endif
@@ -262,3 +261,8 @@ SECTIONS
  */
 ASSERT((_end - _text <= KERNEL_IMAGE_SIZE),
         "kernel image bigger than KERNEL_IMAGE_SIZE")
+
+#ifdef CONFIG_SMP
+ASSERT((per_cpu__irq_stack_union == 0),
+        "irq_stack_union is not at start of per-cpu area");
+#endif