[Crash-utility] invalid regs display in bt

[Dave Anderson]

Richard J Moore wrote:

> On looking at the code in entry.S at page_fault and the other exception 
> entry points I see no attempt to save regs to create a pt_regs struct. 
> The fact that do_page_fault takes pt_regs as the first arg is a hack to 
> get at CS:EIP and SS:ESP at the time of exception. 

KPROBE_ENTRY(page_fault)
	RING0_EC_FRAME
	pushl $do_page_fault
	CFI_ADJUST_CFA_OFFSET 4
	ALIGN
error_code:
	/* the function address is in %fs's slot on the stack */
	pushl %es
	CFI_ADJUST_CFA_OFFSET 4
	/*CFI_REL_OFFSET es, 0*/
	pushl %ds
	CFI_ADJUST_CFA_OFFSET 4
	/*CFI_REL_OFFSET ds, 0*/
	pushl %eax
	CFI_ADJUST_CFA_OFFSET 4
	CFI_REL_OFFSET eax, 0
	pushl %ebp
	CFI_ADJUST_CFA_OFFSET 4
	CFI_REL_OFFSET ebp, 0
	pushl %edi
	CFI_ADJUST_CFA_OFFSET 4
	CFI_REL_OFFSET edi, 0
	pushl %esi
	CFI_ADJUST_CFA_OFFSET 4
	CFI_REL_OFFSET esi, 0
	pushl %edx
	CFI_ADJUST_CFA_OFFSET 4
	CFI_REL_OFFSET edx, 0
	pushl %ecx
	CFI_ADJUST_CFA_OFFSET 4
	CFI_REL_OFFSET ecx, 0
	pushl %ebx
	CFI_ADJUST_CFA_OFFSET 4
	CFI_REL_OFFSET ebx, 0
	cld
	pushl %fs
	CFI_ADJUST_CFA_OFFSET 4
	/*CFI_REL_OFFSET fs, 0*/
	movl $(__KERNEL_PERCPU), %ecx
	movl %ecx, %fs
	UNWIND_ESPFIX_STACK
	popl %ecx
	CFI_ADJUST_CFA_OFFSET -4
	/*CFI_REGISTER es, ecx*/
	movl PT_FS(%esp), %edi		# get the function address
	movl PT_ORIG_EAX(%esp), %edx	# get the error code
	movl $-1, PT_ORIG_EAX(%esp)	# no syscall to restart
	mov  %ecx, PT_FS(%esp)
	/*CFI_REL_OFFSET fs, ES*/
	movl $(__USER_DS), %ecx
	movl %ecx, %ds
	movl %ecx, %es
	movl %esp,%eax			# pt_regs pointer
	call *%edi
	jmp ret_from_exception
	CFI_ENDPROC
KPROBE_END(page_fault)