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linux-interrupts-2: rework pm jump part

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Shorten the sentence to reduce repetition, as the correlation with the boot chapter
is already explained in the previous sentence.
Add 'function' to `protected_mode_jump`

s/We already know from the earliest parts that entry to protected mode is located
  in the `boot_params.hdr.code32_start` and you can see that we pass the entry of
  the protected mode and `boot_params` to the `protected_mode_jump`
 /The entry to protected mode is located in the `boot_params.hdr.code32_start`
  and passed together with the `boot_params` to the `protected_mode_jump` function/

Correct grammatical errors:
s/in the end of the/at the end of/

Improve word choices:
s/gets these two parameters in the/receives these two parameters within the/

Add missing punctuation and add filling words for a more fluent reading.

This commit introduced a new way of annotating functions: (https://lkml.org/lkml/2019/1/30/374)
s/GLOBAL(protected_mode_jump)/SYM_FUNC_START_NOALIGN(protected_mode_jump)/
s/ENDPROC(protected_mode_jump)/SYM_FUNC_END(protected_mode_jump)/
s/GLOBAL(in_pm32)/SYM_FUNC_START_LOCAL_NOALIGN(.Lin_pm32)/
s/ENDPROC(in_pm32)/SYM_FUNC_END(.Lin_pm32)/

This commit made in_pm32 local: (https://lkml.org/lkml/2019/10/11/192)
s/2:     .long   in_pm32/2:     .long   .Lin_pm32/

Signed-off-by: Sebastian Fricke <sebastian.fricke.linux@gmail.com>
This commit is contained in:
Sebastian Fricke 2020-05-02 11:10:46 +02:00
parent d383e52ef7
commit a327d7237b
1 changed files with 9 additions and 14 deletions
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23
Interrupts/linux-interrupts-2.md
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@ -38,41 +38,36 @@ struct gdt_ptr {
Of course in our case the `gdt_ptr` does not represent the `GDTR` register, but `IDTR` since we set the `Interrupt Descriptor Table`. You will not find an `idt_ptr` structure, because if it had been in the Linux kernel source code, it would have been the same as a `gdt_ptr` but with a different name. It would make no sense to create two structures that only differ in their names. Note here that we do not fill the `Interrupt Descriptor Table` with entries, because it is too early to handle any interrupts or exceptions at this point. That's why we just fill the `IDT` with `NULL`. Of course in our case the `gdt_ptr` does not represent the `GDTR` register, but `IDTR` since we set the `Interrupt Descriptor Table`. You will not find an `idt_ptr` structure, because if it had been in the Linux kernel source code, it would have been the same as a `gdt_ptr` but with a different name. It would make no sense to create two structures that only differ in their names. Note here that we do not fill the `Interrupt Descriptor Table` with entries, because it is too early to handle any interrupts or exceptions at this point. That's why we just fill the `IDT` with `NULL`.
After the setup of the [Interrupt descriptor table](http://en.wikipedia.org/wiki/Interrupt_descriptor_table), [Global Descriptor Table](http://en.wikipedia.org/wiki/GDT) and other stuff we jump into [protected mode](http://en.wikipedia.org/wiki/Protected_mode) in the - [arch/x86/boot/pmjump.S](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/boot/pmjump.S). You can read more about it in the [part](https://0xax.gitbooks.io/linux-insides/content/Booting/linux-bootstrap-3.html) which describes the transition to protected mode. After the setup of the [Interrupt descriptor table](http://en.wikipedia.org/wiki/Interrupt_descriptor_table), [Global Descriptor Table](http://en.wikipedia.org/wiki/GDT) and other stuff we jump into [protected mode](http://en.wikipedia.org/wiki/Protected_mode) in the - [arch/x86/boot/pmjump.S](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/boot/pmjump.S) file. You can read more about it in the [part](https://0xax.gitbooks.io/linux-insides/content/Booting/linux-bootstrap-3.html), which describes the transition to protected mode.
We already know from the earliest parts that entry to protected mode is located in the `boot_params.hdr.code32_start` and you can see that we pass the entry of the protected mode and `boot_params` to the `protected_mode_jump` in the end of the [arch/x86/boot/pm.c](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/boot/pm.c): The entry to protected mode is located in the `boot_params.hdr.code32_start` and passed together with the `boot_params` to the `protected_mode_jump` function at the end of [arch/x86/boot/pm.c](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/boot/pm.c):
```C ```C
protected_mode_jump(boot_params.hdr.code32_start, protected_mode_jump(boot_params.hdr.code32_start,
(u32)&boot_params + (ds() << 4)); (u32)&boot_params + (ds() << 4));
``` ```
The `protected_mode_jump` is defined in the [arch/x86/boot/pmjump.S](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/boot/pmjump.S) and gets these two parameters in the `ax` and `dx` registers using one of the [8086](http://en.wikipedia.org/wiki/Intel_8086) calling [conventions](http://en.wikipedia.org/wiki/X86_calling_conventions#List_of_x86_calling_conventions): The `protected_mode_jump` function is defined at [arch/x86/boot/pmjump.S](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/boot/pmjump.S) and receives these two parameters within the `ax` and `dx` registers, using one of the [8086](http://en.wikipedia.org/wiki/Intel_8086) calling [conventions](http://en.wikipedia.org/wiki/X86_calling_conventions#List_of_x86_calling_conventions):
```assembly ```assembly
GLOBAL(protected_mode_jump) SYM_FUNC_START_NOALIGN(protected_mode_jump)
... ...
... ...
... ...
.byte 0x66, 0xea # ljmpl opcode .byte 0x66, 0xea # ljmpl opcode
2: .long in_pm32 # offset 2: .long .Lin_pm32 # offset
.word __BOOT_CS # segment .word __BOOT_CS # segment
... SYM_FUNC_END(protected_mode_jump)
...
...
ENDPROC(protected_mode_jump)
``` ```
where `in_pm32` contains a jump to the 32-bit entry point: where `in_pm32` contains a jump to the 32-bit entry point:
```assembly ```assembly
GLOBAL(in_pm32) SYM_FUNC_START_LOCAL_NOALIGN(.Lin_pm32)
... ...
... ...
jmpl *%eax // %eax contains address of the `startup_32` jmpl *%eax # Jump to the 32-bit entrypoint
... SYM_FUNC_END(.Lin_pm32)
...
ENDPROC(in_pm32)
``` ```
As you can remember the 32-bit entry point is in the [arch/x86/boot/compressed/head_64.S](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/boot/compressed/head_64.S) assembly file, although it contains `_64` in its name. We can see the two similar files in the `arch/x86/boot/compressed` directory: As you can remember the 32-bit entry point is in the [arch/x86/boot/compressed/head_64.S](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/boot/compressed/head_64.S) assembly file, although it contains `_64` in its name. We can see the two similar files in the `arch/x86/boot/compressed` directory: