From f8878845f9cb9d30663a8bb3a3edeb1413a42388 Mon Sep 17 00:00:00 2001 From: "Ronald G. Minnich" Date: Thu, 12 Jul 2012 11:21:51 -0700 Subject: [PATCH] Poison the stack to uncover programming errors Code can easily make the mistake of using uninitialized values or, in assembly, mistakenly dereferencing stack pointers when an address is desired. Set the stack to a non-zero value which is also (by testing) a pointer which will crash coreboot if used. This poisoning has uncovered at least one bug. Change-Id: I4affb9a14b96611e8bf83cb82636e47913025a5d Signed-off-by: Ronald G. Minnich Reviewed-on: http://review.coreboot.org/1221 Reviewed-by: Marc Jones Tested-by: build bot (Jenkins) Reviewed-by: Sven Schnelle --- src/arch/x86/lib/c_start.S | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/src/arch/x86/lib/c_start.S b/src/arch/x86/lib/c_start.S index fd9dce78c5..9c1fdb106f 100644 --- a/src/arch/x86/lib/c_start.S +++ b/src/arch/x86/lib/c_start.S @@ -16,17 +16,21 @@ _start: post_code(POST_ENTRY_C_START) /* post 13 */ - /** clear stack */ + /** poison the stack. Code should not count on the + * stack being full of zeros. This stack poisoning + * recently uncovered a bug in the broadcast SIPI + * code. + */ cld leal _stack, %edi movl $_estack, %ecx subl %edi, %ecx shrl $2, %ecx /* it is 32 bit aligned, right? */ - xorl %eax, %eax + movl $0xDEADBEEF, %eax rep stosl - /** clear bss */ + /** clear bss, which unlike the stack is zero by definition */ leal _bss, %edi movl $_ebss, %ecx subl %edi, %ecx