[PATCH v2 41/44] x86/asm/head: standardize the end of the stack for idle tasks

[Josh Poimboeuf]

Thanks to all the recent x86 entry code refactoring, most tasks' kernel
stacks start at the same offset right above their saved pt_regs,
regardless of which syscall was used to enter the kernel.  That creates
a nice convention which makes it straightforward to identify the end of
the stack, which can be useful for stack walking code which needs to
verify the stack is sane.

However, CPU idle "swapper" tasks don't follow that convention.  Fix
that by starting their stack at a sizeof(pt_regs) offset from the end of
the stack page.

Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 arch/x86/kernel/head_64.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index c910c27..e33081d 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -326,7 +326,7 @@ ENDPROC(start_cpu0)
 	GLOBAL(initial_gs)
 	.quad	INIT_PER_CPU_VAR(irq_stack_union)
 	GLOBAL(initial_stack)
-	.quad  init_thread_union+THREAD_SIZE-8
+	.quad  init_thread_union + THREAD_SIZE - SIZEOF_PTREGS
 	__FINITDATA
 
 bad_address:
-- 
2.7.4