Commit 6616a147 authored Sep 21, 2016 by Josh Poimboeuf Committed by Ingo Molnar Oct 20, 2016

x86/boot/32: Fix the end of the stack for idle tasks



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@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nilay Vaish <nilayvaish@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/2588f34b6fbac4ae6f6f9ead2a78d7f8d58a6341.1474480779.git.jpoimboe@redhat.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 4d516f41

arch/x86/kernel/head_32.S

+5 −3

Original line number	Original line	Diff line number	Diff line
	@@ -289,7 +289,8 @@ num_subarch_entries = (. - subarch_entries) / 4
	ENTRY(start_cpu0)		ENTRY(start_cpu0)
	movl initial_stack, %ecx		movl initial_stack, %ecx
	movl %ecx, %esp		movl %ecx, %esp
	jmp *(initial_code)		call *(initial_code)
			1: jmp 1b
	ENDPROC(start_cpu0)		ENDPROC(start_cpu0)
	#endif		#endif

	@@ -470,8 +471,9 @@ ENTRY(startup_32_smp)
	xorl %eax,%eax # Clear LDT		xorl %eax,%eax # Clear LDT
	lldt %ax		lldt %ax

	pushl $0 # fake return address for unwinder		call *(initial_code)
	jmp *(initial_code)		1: jmp 1b
			ENDPROC(startup_32_smp)

	#include "verify_cpu.S"		#include "verify_cpu.S"