[PATCH v2 4/9] x86/head/32: fix the end of the stack for idle tasks

From: Josh Poimboeuf
Date: Wed Sep 21 2016 - 17:04:46 EST

The frame at the end of each idle task stack is inconsistent with real
task stacks, which have a stack frame header and a real return address
before the pt_regs area. This inconsistency can be confusing for stack
unwinders. It also hides useful information about what asm code was
involved in calling into C.

Fix that by changing the initial code jumps to calls. Also add infinite
loops after the calls to make it clear that the calls don't return, and
to hang if they do.

Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
arch/x86/kernel/head_32.S | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index 617fba2..7aac1b9 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -288,7 +288,8 @@ num_subarch_entries = (. - subarch_entries) / 4
movl initial_stack, %ecx
movl %ecx, %esp
- jmp *(initial_code)
+ call *(initial_code)
+1: jmp 1b

@@ -469,8 +470,9 @@ ENTRY(startup_32_smp)
xorl %eax,%eax # Clear LDT
lldt %ax

- pushl $0 # fake return address for unwinder
- jmp *(initial_code)
+ call *(initial_code)
+1: jmp 1b

#include "verify_cpu.S"