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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 // trigger a page fault
unsafe { unsafe {
*(0xdeadbeaf as *mut u64) = 42; *(0xdeadbeef as *mut u64) = 42;
}; };
println!("It did not crash!"); 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: 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. 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. 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. 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: 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. 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. 3. The CPU jumps to the – now present – double fault handler.