crash-utility-bounces@xxxxxxxxxx wrote on 27/09/2007 17:13:45:
> Richard J Moore wrote:
> >
> > crash-utility-bounces@xxxxxxxxxx wrote on 27/09/2007 15:45:21:
> >
> > > 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)
> > >
> >
> > Dave, it looks like error_code: has been change relatively
recently. My
> > source starts:
> > error_code:
> > pushl %ds
> > pushl %eax
> > xorl %eax,%eax
> > pushl %ebp
> > > > and so on. Clearly not a valid pt_regs struct.
> > The source I'm working with is from FC5. On your version of the
kernel
> > only the ERR, SS and ESP would be invalid.
> > What tree is yours taken from?
> >
>
> My example was from upstream 2.6.22-5. RHEL5 (2.6.18-based)
> is slightly different, as the "error_code:" chunk is located
> in the "divide_error" entry point, but like 2.6.22-5, all of
> the other exceptions jmp to it.
>
> But even your code is creating the remainder of the pt_regs
> after the essential registers laid down by the hardware
> exception mechanism, by pushing the remaining registers,
> "upwards" towards the beginning of the structure:
>
> struct pt_regs {
> long ebx;
> long ecx;
> long edx;
> long esi;
> long edi;
> long ebp;
> long eax;
> int xds;
> int xes;
> long orig_eax;
> long eip;
> int xcs;
> long eflags;
> long esp;
> int xss;
> };
>
> Right?
>
> Dave
>
I don't think so. Am I misreading this:
we take a page fault at ring 0. The cpu pushes eflags, cs, eip,
error-code
we enter the kernel at:
ENTRY(page_fault)
pushl $do_page_fault
jmp error_code
we have errror code in orig_eax
error_code:
pushl %ds
pushl %eax
xorl %eax, %eax
pushl %ebp
pushl %edi
pushl %esi
pushl %edx
decl %eax # eax = -1
pushl %ecx
pushl %ebx
cld
pushl %es
UNWIND_ESPFIX_STACK
popl %ecx
movl ES(%esp), %edi # get the function address
movl ORIG_EAX(%esp), %edx # get the error code
movl %eax, ORIG_EAX(%esp)
movl %ecx, ES(%esp)
movl $(__USER_DS), %ecx
movl %ecx, %ds
movl %ecx, %es
movl %esp,%eax # pt_regs pointer
call *%edi
jmp ret_from_exception
Aren't we sorting ds in the pt_regs.ES ? and therefore one register out?
Maybe I'm missing something?
