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Update interrupts-1.md

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0xAX 2015-08-23 23:51:22 +06:00
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interrupts/interrupts-1.md
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@ -374,33 +374,7 @@ for_each_possible_cpu(cpu) {
} }
``` ```
Here we go over all the CPUs on-by-one and setup `irq_stack_ptr`. This turns out to be equal to the top of the interrupt stack minus `64`. Why `64`? If you remember, we set the stack canary in the beginning of the `start_kernel` function from the [init/main.c](https://github.com/torvalds/linux/blob/master/init/main.c) with the call of the `boot_init_stack_canary` function: Here we go over all the CPUs on-by-one and setup `irq_stack_ptr`. This turns out to be equal to the top of the interrupt stack minus `64`. Why `64`?TODO [arch/x86/kernel/cpu/common.c](https://github.com/torvalds/linux/blob/master/arch/x86/kernel/cpu/common.c) source code file is following:
```C
static __always_inline void boot_init_stack_canary(void)
{
u64 canary;
...
...
...
#ifdef CONFIG_X86_64
BUILD_BUG_ON(offsetof(union irq_stack_union, stack_canary) != 40);
#endif
//
// getting canary value here
//
this_cpu_write(irq_stack_union.stack_canary, canary);
...
...
...
}
```
Note that `canary` is `64` bits value. That's why we need to subtract `64` from the size of the interrupt stack to avoid overlapping with the stack canary value. Initialization of the `irq_stack_union.gs_base` is in the `load_percpu_segment` function from the [arch/x86/kernel/cpu/common.c](https://github.com/torvalds/linux/blob/master/arch/x86/kernel/cpu/common.c):
TODO maybe more about the wrmsl
```C ```C
void load_percpu_segment(int cpu) void load_percpu_segment(int cpu)