lkml.org 
[lkml]   [2016]   [Aug]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH v3 14/51] x86/asm/head: put real return address on idle task stack
On Fri, Aug 12, 2016 at 7:28 AM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> The frame at the end of each idle task stack has a zeroed return
> address. This is inconsistent with real task stacks, which have a real
> return address at that spot. This inconsistency can be confusing for
> stack unwinders.
>
> Make it a real address by using the side effect of a call instruction to
> push the instruction pointer on the stack.
>
> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> ---
> arch/x86/kernel/head_64.S | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
> index 3621ad2..c90f481 100644
> --- a/arch/x86/kernel/head_64.S
> +++ b/arch/x86/kernel/head_64.S
> @@ -298,8 +298,9 @@ ENTRY(start_cpu)
> * REX.W + FF /5 JMP m16:64 Jump far, absolute indirect,
> * address given in m16:64.
> */
> - movq initial_code(%rip),%rax
> - pushq $0 # fake return address to stop unwinder
> + call 1f # put return address on stack for unwinder
> +1: xorq %rbp, %rbp # clear frame pointer
> + movq initial_code(%rip), %rax
> pushq $__KERNEL_CS # set correct cs
> pushq %rax # target address in negative space
> lretq
> --
> 2.7.4
>

Seems reasonable.

Reviewed-by: Andy Lutomirski <luto@kernel.org>

--Andy

\
 
 \ /
  Last update: 2016-09-17 09:56    [W:0.303 / U:0.732 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site