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Typo: deadbeaf -> deadbeef

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Philipp Oppermann
2018-07-23 11:07:49 +02:00
parent 71e35cef4d
commit f551116714
1 changed files with 4 additions and 4 deletions
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8
blog/content/second-edition/posts/07-double-faults/index.md
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@@ -37,7 +37,7 @@ pub extern "C" fn _start() -> ! {
// trigger a page fault
unsafe {
*(0xdeadbeaf as *mut u64) = 42;
*(0xdeadbeef as *mut u64) = 42;
};
println!("It did not crash!");
@@ -45,11 +45,11 @@ pub extern "C" fn _start() -> ! {
}
```
We use `unsafe` to write to the invalid address `0xdeadbeaf`. The virtual address is not mapped to a physical address in the page tables, so a page fault occurs. We haven't registered a page fault handler in our [IDT], so a double fault occurs.
We use `unsafe` to write to the invalid address `0xdeadbeef`. The virtual address is not mapped to a physical address in the page tables, so a page fault occurs. We haven't registered a page fault handler in our [IDT], so a double fault occurs.
When we start our kernel now, we see that it enters an endless boot loop. The reason for the boot loop is the following:
1. The CPU tries to write to `0xdeadbeaf`, which causes a page fault.
1. The CPU tries to write to `0xdeadbeef`, which causes a page fault.
2. The CPU looks at the corresponding entry in the IDT and sees that the present bit isn't set. Thus, it can't call the page fault handler and a double fault occurs.
3. The CPU looks at the IDT entry of the double fault handler, but this entry is also non-present. Thus, a _triple_ fault occurs.
4. A triple fault is fatal. QEMU reacts to it like most real hardware and issues a system reset.
@@ -88,7 +88,7 @@ When we start our kernel now, we should see that the double fault handler is inv
It worked! Here is what happens this time:
1. The CPU executes tries to write to `0xdeadbeaf`, which causes a page fault.
1. The CPU executes tries to write to `0xdeadbeef`, which causes a page fault.
2. Like before, the CPU looks at the corresponding entry in the IDT and sees that the present bit isn't set. Thus, a double fault occurs.
3. The CPU jumps to the – now present – double fault handler.