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boot: add missed set_bios_mode()

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This commit is contained in:
Alexander Kuleshov 2017-09-10 17:27:51 +06:00
parent 8d76549828
commit 117dbf29a1
1 changed files with 18 additions and 0 deletions
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Booting/linux-bootstrap-2.md
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@ -397,6 +397,24 @@ You can see the result of this in the `dmesg` output, something like:
[ 0.000000] BIOS-e820: [mem 0x00000000fffc0000-0x00000000ffffffff] reserved [ 0.000000] BIOS-e820: [mem 0x00000000fffc0000-0x00000000ffffffff] reserved
``` ```
Next we may see call of the `set_bios_mode` function after physical memory is detected. As we may see, this function is implemented only for the `x86_64` mode:
```C
static void set_bios_mode(void)
{
#ifdef CONFIG_X86_64
struct biosregs ireg;
initregs(&ireg);
ireg.ax = 0xec00;
ireg.bx = 2;
intcall(0x15, &ireg, NULL);
#endif
}
```
The `set_bios_mode` executes `0x15` BIOS interrupt to tell the BIOS that [long mode](https://en.wikipedia.org/wiki/Long_mode) (in a case of `bx = 2`) will be used.
Keyboard initialization Keyboard initialization
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