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)
--
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