Interrupt and exception

Link to process stack from irq stack

commit a2bbe75089d5eb9a3a46d50dd5c215e213790288
x86: Don’t use frame pointer to save old stack on irq entry
/* Save previous stack value /
movq %rsp, %rsi

2: /
Store previous stack value */
pushq %rsi
Obtain sys_call_table on amd64



native_init_IRQ()-> set_intr_gate(i, irq_entries_start…
irq_entries_start define in arch/x86/kernel/entry_32.S

##Interrupt Context terminology
* in_irq
in __irq_enter I found preempt_count_add(HARDIRQ_OFFSET) only in here!
+irq disable 部设计preempt_cout

  • in_softirq
    should rename to in_softirq_or_bh_disable()
    local_bh_disable use SOFTIRQ_DISABLE_OFFSET (2 * SOFTIRQ_OFFSET)
    __do_softirq use __local_bh_disable_ip(_RETIP, SOFTIRQ_OFFSET), damn it!

  • in_interrupt
    一种是irq路径上的do_softirq, 即in_serving_softirq
    //not in softirq context!!!
    local_irq_disable,不是, 但是no operation with preempt_count() 这种情况x86 in_interrupt是无感的.use irqs_disabled to check
    [Question about in_interrupt() semantics with regard to softirqs]()

##When to save irq rather than just disable irq
local_irq_disable() used in the code path that never disabled interrupts.
local_irq_save(flags) used in the code path that already disabled interrupts.

##what about irq nested?

Triggering a #GP exception

if you do lidt in userspace program, you will receive SIGSEGV with si_code 128(somewhere of kernel).
But with the dmesg traps: int0x80[15066] general protection ip:4000c7 sp:7ffc8706cdf0 error:0 in int0x80[400000+1000] form do_general_protection.
Privilege instructions in V3a chapter 5 Protection
.quad msg

.ascii “Hello, world!\n”
len = . - msg
.long 0,0

.global _start

movl $4, %eax
movl $1, %ebx
movl $msg, %ecx
sidt saved_idt
lidt saved_idt ;===============> crashed at here
movl $len, %edx
int $0x80

movl  $1, %eax
xorl  %ebx, %ebx 
int   $0x80